Hostname: page-component-7c8c6479df-27gpq Total loading time: 0 Render date: 2024-03-28T01:10:00.448Z Has data issue: false hasContentIssue false

Does physical exercise modify antioxidant requirements?

Published online by Cambridge University Press:  01 June 2008

I. Margaritis
Affiliation:
French Food Safety Agency, Department for Evaluation of Nutritional and Health Risk, Maisons-Alfort, France
A. S. Rousseau*
Affiliation:
Inserm U907, Université de Nice Sophia Antipolis, Faculté de Médecine, 28 Avenue de Valombrose, 06107Nice Cedex 2, France
*
*Corresponding author: Dr Anne-Sophie Rousseau, fax +33 4 93 81 54 32, email Anne-Sophie.ROUSSEAU@unice.fr
Rights & Permissions [Opens in a new window]

Abstract

Physical training is known to induce a biochemical adaptive response which might require an increase in the ingestion and/or the absorption of micronutrients. A question that is still being raised is whether acute or chronic exercise modifies antioxidant requirements. First, the present review brings to light the most crucial studies on the topic. Second, it interprets the established relationships between antioxidant micronutrient intakes and the adaptive response of antioxidant systems. Finally, it exposes the major questions connected with antioxidant micronutrient requirements for athletes. To this effect, the training-load interaction with nutrition is taken into account. As oxidative stress cannot be avoided, the imbalance between oxidants and antioxidants can be alleviated to minimise oxidative damage and outcomes. There is growing evidence that one specific antioxidant cannot by itself prevent oxidative stress-induced damage, as direct adverse effects of supplementation are attributed to undesirable synergic effects. Other effects can be supposed that limit the endogenous adaptive effect of training. High doses of antioxidant supplements can minimise the effects of radical oxygen species themselves or generate pro-oxidant effects. Effects are only exhibited when nutritional status is deficient. There are no convincing effects of supplementation in well-trained athletes. Risk/benefit analysis emerges on evidence for an unknown risk of supranutritional intakes, a supposed impairment of adaptive effects and a still unknown long-term risk. Appropriate status can be achieved by a diversified and balanced diet, adapted to specific needs, by awareness of high-density food intakes (avoiding products containing a low density of micronutrients).

Type
Research Article
Copyright
Copyright © The Authors 2008

Introduction

Antioxidant vitamins and trace element intakes are necessary to allow endogenous adaptation and to avoid excessive stress. This could induce various forms of cellular damage, the alteration of cellular functions, and, in the case of excessive stress, cellular death by apoptosis or necrosis. Nowadays, few athletes ignore that physical exercise promotes oxidative stress. Based on this, antioxidant nutrient requirements have been arousing growing interest during the past decade.

The French Food Agency has been asked to assess enriched foods for athletes. To date, the question of exercise-induced oxidative stress brings out the question of the optimal conditions for the adaptation of antioxidants. Inefficient antioxidant systems make one vulnerable to the outcome of oxidative stress. Requirements for macronutrients in adults have been widely described. However, considering micronutrients, the ones which have to be considered are those which might be ingested in an insufficient way and those which may be lost in excess during physical exercise. Another reason for considering these micronutrients is linked to the assumption that training induces a biochemical adaptive response which might require an increase in the ingestion and/or the absorption of trace elements and vitamins. Consequently, several authors have put forward the hypothesis that for some athletes, their intake of certain antioxidant micronutrients might be less than they actually need. So far, whether acute or chronic physical exercise induces a change in antioxidant and trace element requirements has not been sufficiently discussed. The question of RDA for athletes has yet to be addressed. This must be done in relation to other fields such as increased losses of micronutrients and the dietary behaviour which changes alongside the goals of the competition. The first step is to make an inventory of the questions raised and to interpret the established relationships between micronutrient intakes and the adaptive responses of the antioxidant system. The second step is to expose the major questions connected with antioxidant micronutrient requirements for athletes, taking into account the training-load interaction with nutrition.

Does physical exercise modify the status of antioxidant vitamins, carotenoids and flavonoids?

Vitamin C

Due to its implication in several metabolic pathways such as carnitine, noradrenalin and collagen synthesis, as well as in antioxidant defence, it is legitimate to say that the athletes' ascorbic acid (vitamin C) requirements are greater because of a higher rate of endogenous consumption compared with individuals who are not physically active. The human diet contains both ascorbic acid and dehydroascorbic acid, the bioavailability of which is supposed to be comparable. These compounds are almost completely absorbed in the ileum by an active transport which becomes passive in the case of ingestion of a high vitamin C dose(Reference Wilson1). Lack of storage implies a requirement for regular dietary intake. High vitamin C intakes increase its excretion in urine, the main elimination pathway. Plasma ascorbic acid is strongly linked to vitamin C intakes – for intakes between 50 and 90 mg/d – and it is shown to be maximal for vitamin C intakes of 200 mg/d(Reference Levine, Wang, Padayatty and Morrow2).

Basal concentrations of ascorbic acid in plasma in some athletes can be low and in some cases reach marginal concentrations(Reference Bergholm, Mäkimattila, Valkonen, Liu, Lahdenperä, Taskinen, Sovijärvi, Malmberg and Yki-Järvinen3Reference Schröder, Navarro, Tramullas, Mora and Galiano5). These athletes are mostly those involved in team games or those undergoing unusual periods of intensive training. Due to an absence of a parallel investigation on their dietary vitamin C intakes, it becomes difficult to interpret these data. In fact, team-game athletes frequently have poor dietary food choices with vitamin C intakes < 150 mg/d(Reference Rousseau, Hininger, Palazzetti, Faure, Roussel and Margaritis6). Moreover, excessive training is backed by the shortage in the supply of vitamin C(Reference Palazzetti, Rousseau, Richard, Favier and Margaritis7). However, with well-trained athletes, ascorbic acid status in basal conditions is normal(Reference Rousseau, Hininger, Palazzetti, Faure, Roussel and Margaritis6). In addition, for most cases, athletes have a higher basal ascorbic acid status than those observed in less physically active individuals(Reference Rousseau, Hininger, Palazzetti, Faure, Roussel and Margaritis6, Reference Cazzola, Russo-Volpe, Cervato and Cstaro8, Reference Evelson, Gambino, Travacio, Jaita, Verona, Maroncelli, Wikinski, Llesuy and Brites9). Dietary intakes, without supplements, can reach 400 mg/d. The relationship between vitamin C intakes and plasma ascorbic acid concentrations is logarithmic in athletes. The optimal bioavailability of vitamin C is shown to be reached with an intake of 200 mg/d(Reference Rousseau, Hininger, Palazzetti, Faure, Roussel and Margaritis6). As a consequence, any supplement above this threshold of intake has no effect on vitamin C plasma concentrations(Reference Schröder, Navarro, Tramullas, Mora and Galiano5, Reference Kanter, Nolte and Holloszy10, Reference Telford, Catchpole, Deakin, McLeay and Plank11).

Even though there is a high nutritional density in vitamin C intakes as observed amongst highly trained athletes, paradoxically these athletes are high consumers of supplements. The consumption of supplements can generate pro-oxidant effects when the intake is above 500 mg/d(Reference Podmore, Griffiths, Herbert, Mistry, Mistry and Lunec12). With well-trained athletes, supplement intakes are frequently observed and can lead to increased lipoperoxidation indices when measured at rest or shortly after exercise(Reference Bryant, Ryder, Martino, Kim and Craig13). This pro-oxidant effect of vitamin C could be worsened by eccentric exercise due to sizeable muscle injuries induced by such(Reference Childs, Jacobs, Kaminski, Halliwell and Leeuwenburgh14). This can lead to muscle damage and/or haemolysis, leading to the release of Fe, normally stored and chelated. It is conceivable that this induces radical oxygen species (ROS) generation through the Fenton reaction, the rate of which is low in normal physiological conditions. High vitamin C intake also reduces the absorption of Cu and increases Fe absorption to the detriment of intestinal absorption of Zn(Reference Sandström15). This accelerated rate of Fe absorption can be detrimental when Fe stores are already abundant. These Fe stores may be abundant amongst top athletes, mainly because of their current uncontrolled practice of Fe supplementation(Reference Zoller and Vogel16). It is also questionable whether the pro-oxidant effect of high doses is due to an imbalance between ascorbic acid and dehydroascorbic acid intakes.

After intensive exercise, natural antioxidant systems, which protect neutrophils, could be depleted. To this effect, the oxidative burst will not be carried out in an effective way. Athletes, in order to avoid infections, make use of preventive and chronic high doses (>500 mg/d) of vitamin C. The supply in vitamin C may be beneficial for some subjects involved in heavy exercising while facing problems with frequent upper respiratory tract infections(Reference Hemila17) but the supplementation in vitamin C, as of now, has generally failed to show consistent results in improving oxidative burst activity (for a review, see Moreira et al. (Reference Moreira, Kekkonen, Delgado, Fonseca, Korpela and Haahtela18)). Nevertheless, there is no evidence that a prolonged consistent intake of vitamin C is favourable to antioxidant system reinforcement and training adaptation. A recent study carried out by Gomez-Cabrera et al. (Reference Gomez-Cabrera, Domenech, Romagnoli, Arduini, Borras, Pallardo, Sastre and Viña19) showed that the supply of 1 g vitamin C/d alleviates training-induced up-regulation of the mitogenic pathway and takes a toll on the improvement of the endurance capacity within a period of 8-week training done by rats which were initially sedentary. This also applies to humans. In the study by Gomez-Cabrera et al. (Reference Gomez-Cabrera, Domenech, Romagnoli, Arduini, Borras, Pallardo, Sastre and Viña19), the expression of PPAR-γ coactivator 1, the main transcription factor of mitogenesis which has recently been shown to be a redox-sensitive process(Reference St-Pierre, Drori and Uldry20), was decreased with a supplementary intake in vitamin C. The study of Khassaf et al. (Reference Khassaf, McArdle, Esanu, Vasilaki, McArdle, Griffiths, Brodie and Jackson21) showed that the heat shock protein HSP70 content in a muscle has a 6-fold increase under normal resting conditions after an 8-week vitamin C intake (500 mg/d). Moreover, HSP70 muscle content is 4·5-fold higher following exercise. This is not the case under resting conditions where it has a 3·5-fold increase amongst individuals receiving a supplement of vitamin C. The results of these studies could be interpreted as a lower adaptive response to exercise due to long-term supplies. To this effect, a question is raised about the effect of exogenous antioxidant supply on the adaptive process. A recent study produced evidence on the failure of muscles to return to normal functioning after exercise following a supply of 1 g vitamin C. This takes place despite the fact that lipoperoxidation markers were concomitantly decreased(Reference Close, Ashton, Cable, Doran, Holloway, McArdle and MacLaren22). Lowering oxidative stress by antioxidant supplement may hamper normal muscle recovery function which is known to depend on ROS level.

It is admitted that the needs of athletes are higher than those of less active individuals, although a well-balanced diet which covers energetic needs provides the necessary vitamin C supply (>200 mg/d). High-training-stress periods are key periods for vitamin C deficit awareness. This nutritional risk of deficit can be reduced by a regular fruit and vegetable consumption.

Vitamin E

It is well known that muscle cell integrity requires an adequate α-tocopherol (vitamin E) status(Reference Coombes, Rowell, Dodd, Demirel, Naito, Shanely and Powers23). Despite the fact that in most cases the intakes of vitamin E amongst well-trained athletes are below 12 mg/d, which is the RDA for the general population, this population is not at risk of marginal status(Reference Rousseau, Hininger, Palazzetti, Faure, Roussel and Margaritis6). As aerobic training increases HDL concentrations, the main plasma lipoprotein carrier of α-tocopherol, α-tocopherol incorporation in tissues is favoured. Indeed, the concentration of α-tocopherol in plasma and muscles is linked to the α-tocopherol incorporation rate which depends on the quantity of specific receptors such as scavenger receptor class B, type I (SR-BI)(Reference Mardones and Rigotti24, Reference Borel, Moussa and Reboul25). These receptors are efficient vectors for α-tocopherol incorporation in muscle cells through their specific recognition of HDL(Reference Mardones and Rigotti24).

One has to be cautious when interpretating plasma α-tocopherol concentrations during training periods. Indeed, the higher the intensity in training is, the higher plasma α-tocopherol concentrations are(Reference Palazzetti, Rousseau, Richard, Favier and Margaritis7). Exercise mobilises more plasma α-tocopherol and leads to an increase in circulating concentrations(Reference Aguiló, Tauler, Pilar Guix, Villa, Córdova, Tur and Pons26, Reference Pincemail, Deby, Camus, Pirnay, Bouchez, Massaux and Goutier27). Besides, high basal values of plasma α-tocopherol can be sometimes associated with high oxidative damage indices(Reference Okamura, Doi, Hamada, Sakurai, Yoshioka, Mitsuzono, Migita, Sumida and Sugawa-Katayama28). High concentrations found in athletes can be explained by the acceleration of its turnover with exercise-induced oxidative stress(Reference Mastaloudis, Leonard and Traber29). Within a short recovery period, plasma α-tocopherol concentrations could remain high. Consequently, the variation in training loads must be taken into account when interpreting α-tocopherol status. With well-led aerobic training, the increase in the concentration of α-tocopherol in plasma is not so visible(Reference Aguiló, Tauler, Pilar Guix, Villa, Córdova, Tur and Pons26). Women also have to be considered separately, as they have higher α-tocopherol concentrations in tissues compared with men(Reference Tiidus30, Reference Tiidus, Behrens, Madere and Houston31). They appear to be less vulnerable to an additional stress generated by low dietary vitamin E intakes(Reference Kelly, Tiidus, Houston and Noble32). Additional antioxidant protection provided by oestrogens, whose chemical properties are similar to α-tocopherol, can spare tissue α-tocopherol in situations of oxidative stress.

Even if no clinical symptoms have been shown with long-term effects of a marginal intake in vitamin E, outcomes of deficit can be mostly shown in response to an inhabitual acute or chronic physical stress such as with overloaded training, ageing, hypoxia exposure or amenorrhoea (in women). In those situations, vitamin E supplementation can exhibit protective effects against oxidative damage of lipid and DNA(Reference Hartmann, Niess, Grunert-Fuchs, Poch and Speit33Reference Rokitzki, Logemann, Huber, Keck and Keul35). Such protective effects of vitamin E supplementation are not shown in well-trained athletes(Reference Buchman, Killip, Ou, Rognerud, Pownall, Dennis and Dunn36). In most cases, pharmacological doses of vitamin E supplementation have little effect on muscle concentrations since the expression of SR-BI receptors decreases in response to high muscle α-tocopherol concentrations(Reference Witt, Kolleck, Fechner, Sinha and Rustow37).

Recent studies have shown that high-dose supplementation of α-tocopherol (536 mg/d) increases exercise-induced oxidative stress(Reference McAnulty, McAnulty, McAnulty, Nieman, Morrow, Shooter, Holmes, Heward and Henson38, Reference Nieman, Henson, McAnulty, McAnulty, Morrow, Ahmed and Heward39). Indeed, the radical form of α-tocopherol can react with the peroxide form of polyunsaturated fatty acid. In vivo, this pro-oxidant reaction is prevented by reducing α-tocopheryl radicals with ascorbic acid (at the interface between membrane and cytosol) or with ubiquinol (in the membrane)(Reference Herrera and Barbas40) and can be achieved with a high-content antioxidant diet.

Carotenoids

Carotenoids are fat-soluble compounds contained in fruits and vegetables. Major circulating carotenoids are β-carotene, lycopene, lutein, α-carotene, β-cryptoxanthin and zeaxanthin. Mechanisms through which carotenoids neutralise free radicals have been described in vitro (Reference Krinsky and Yeum41). There has been evidence of the antioxidant effect of carotenoids mainly in the mechanism of the neutralisation of singlet oxygen (1O2) generated during the photo-oxidation process. Competition during carotenoid absorption and transport, as well as synergies between the two processes, are both very complex. The food matrix effect is high for these nutrients. For example, the absorption of β-carotene present in vegetables is limited by their content of lutein whose bioavailability in vegetables is 5-fold that of β-carotene(Reference van het Hof, Brouwer, West, Haddeman, Steegers-Theunissen, van Dusseldorp, Weststrate, Eskes and Hautvast42).

During overloaded and/or inhabitual training, the concentrations of plasma β-carotene, which is transiently lowered under normal training conditions, remains low during the phase of recovery(Reference Bergholm, Mäkimattila, Valkonen, Liu, Lahdenperä, Taskinen, Sovijärvi, Malmberg and Yki-Järvinen3, Reference Aguiló, Tauler, Pilar Guix, Villa, Córdova, Tur and Pons26, Reference Sumida, Doi, Sakurai, Yoshioka and Okamura43). Moreover, the drop in the concentration of carotenoids with age is steeper when individuals carry out recurrent exercise(Reference Rousseau, Margaritis, Arnaud, Faure and Roussel44). This suggests that carotenoid requirements, and especially β-carotene, increase with age and physical activity. With well-trained athletes, the prevalence of marginal plasma β-carotene concentrations (2·9 % of women and 18·5 % of men) is not higher than that found in the general population(Reference Rousseau, Hininger, Palazzetti, Faure, Roussel and Margaritis6). However, the lower the sum total of carotenoid plasma concentration is, the higher the plasma lipoperoxidation marker(Reference Rousseau, Hininger, Palazzetti, Faure, Roussel and Margaritis6) is.

Among the antioxidant complex supplements given to athletes highly exposed to oxidative stress – especially in extreme conditions such as cold or high altitude – those containing β-carotene or multiple carotenoids at nutritional doses fight lipoperoxidation with more efficiency in individuals with low initial antioxidant status(Reference Schröder, Navarro, Tramullas, Mora and Galiano5, Reference Kanter, Nolte and Holloszy10, Reference Schmidt, Askew, Roberts, Prior, Ensign and Hesslink45). The origin of free radical production influences the effect of ingested antioxidant vitamins and carotenoids. In LDL, α-carotene and β-carotene are the main targets of NO-induced oxidation and are, in some situations, even more oxidised than α-tocopherol(Reference Kontush, Weber and Beisiegel46).

There is growing evidence that one antioxidant cannot act alone to prevent oxidative damage. The pertinence of a well-balanced antioxidant diet is to date well proven. The combined action of multiple compounds derived from a diet rich in fruits and vegetables cannot be replaced by a supplementation with a single or a combination of antioxidants. Synergic effects of vitamins C and E and carotenoids(Reference Niki, Noguchi, Tsuchihashi and Gotoh47), as well as micronutrient competitions during intestinal absorption, suggest that the best way to avoid any nutritional error is to take a close look at how food works and what it provides specifically.

Flavonoids

The major groups of flavonoids in the human diet are the flavonols, proanthocyanidins (which include catechins), isoflavonoids, flavones, and flavanones. Due to their polyphenolic nature, flavonoids (found in abundance in plants) have antioxidant effects which vary according to their nature and quantity. Although their structure is close to α-tocopherol, flavonoids seem to have more of a synergistic mode of action with vitamins E and C than a sparing effect in the case of deficit in vitamin E(Reference Chen, Milbury, Lapsley and Blumberg48, Reference Ameho, Chen, Smith, Sanchez-Moreno, Milbury and Blumberg49). Flavonoids provide a protection against peroxynitrite effects by ‘scavenging’ its two precursors, NO and the superoxide anion(Reference Klotz and Sies50). However, their protective effects on the vascular system are not only related to their antioxidant capacity. Among these flavonoids, quercetin, the major representative flavonoid subclass of flavonols, catechins and epicatechins are best known for their antioxidant capacities. High amounts of quercetin are generally found in tea, apples, red wine, broccoli, citrus fruits and red fruits. Oligomeric catechins are highly concentrated in red wine, grapes, cocoa, cranberries and apples. Other polyphenols such as soya isoflavones, mostly genistein, also have in vitro antioxidant capacities(Reference Ruiz-Larrea, Mohan, Paganga, Miller, Bolwell and Rice-Evans51). Due to its ‘oestrogen-like’ effect, genistein is shown to mimic the effects of oestrogens via the activation of mitogen-activated protein kinases and NF-κB, leading to an up-regulation of the antioxidant enzyme Mn superoxide dismutase (SOD) gene expression(Reference Viña, Sastre, Pallardó, Gambini and Borrás52).

Polyphenol pharmacokinetics are generally characterised by a plasma peak from 5–8 h after absorption, and a persistence of significant rates up to 24–36 h. With regards to quercetin, its plasma concentration peak as well as its elimination varies according to the food source(Reference de Vries, Hollman, Meyboom, Buysman, Zock, van Staveren and Katan53). In the case of repeated intakes, a plateau whose value depends on the proportion introduced is reached(Reference de Vries, Hollman, Meyboom, Buysman, Zock, van Staveren and Katan53). Determining the daily contributions remains, however, limited by the still incomplete tables of composition of food in flavonoids.

In spite of their known antioxidant effect, and unlike vitamins C and E and β-carotene research which has many clinical experiments, there has been little experimentation done with polyphenols on human subjects, including athletes. To the best of our knowledge, the study carried out by Panza et al. (Reference Panza, Wazlawik, Ricardo Schutz, Comin, Hecht and da Silva54) stands out as the only one that has produced evidence, among the studies carried out, about the effects on indices of oxidative stress. These authors showed that a contribution in green tea (4·6 g phenolic compounds/d) increased glutathione concentrations and decreased the indices of oxidative damage on the lipids observed within 1 min and 15 min after a resistance exercise by lowering xanthine oxidase activity. Quercetin supplementation at 1 g/d in trained cyclists over a 24 d period diminished post-exercise expression of leucocyte IL-8 and IL-10 mRNA but had no effect on muscle concentrations of NF-κB(Reference Nieman, Henson and Davis55), which ROS generated during exercise are known to serve as critical messengers to activate upstream kinases of its cascade. The antioxidant effect is suggested not to be enough to induce a decrease in NF-κB synthesis, as quercetin ingestion does not exert protection from exercise-induced oxidative stress and inflammation(Reference McAnulty, McAnulty and Nieman56). However, such a supplementation led to marked differences in rates of illness (5 v. 45 %, respectively, in the supplemented and placebo group) during the 2-week period after intensified exercise without concomitant changes in several measures of immune function(Reference Nieman, Henson and Gross57). Results of supplementation in clinical experiments are also inconclusive regarding isoflavone supplementation. Their effects on antioxidant systems may not be potent enough to diminish an abrupt surge of oxidative stress due to acute exercise(Reference Chen, Milbury, Lapsley and Blumberg48). However, it is still unknown if a chronic intake of ‘oestrogen-like’ isoflavones can decrease the endogenous adaptive response. Further investigation before conclusions can be reached regarding benefits in humans, and even more so in women and women athletes, is needed.

Even though the quantities generally contained in supplements do not seem to present genotoxic effects, high doses of these dietary compounds can also be toxic and mutagenic in cell-culture systems and excess consumption by mammals could cause adverse metabolic reactions(Reference Duthie, Johnson and Dobson58). Moreover, inhibitory effects of non-haeme Fe absorption have been evidenced(Reference Hurrell, Reddy and Cook59). This property is important to consider when giving dietary advice to athletes who are more susceptible to developing Fe deficiency, in particular, those involved in overloaded training and/or those having a vegetarian or vegan diet.

Whatever the case, the complementary, additive, and/or synergistic effects resulting from multiple phytochemicals found in the flavonoid-rich foods are responsible for their wide range of observed biological properties rather than these effects being due to a single constituent alone(Reference Chun, Chung, Claycombe and Song60, Reference Williamson and Manach61). The studies available are not sufficient enough for the risk/benefit assessment of the supplementation of flavonoids.

Does physical activity modify the status of antioxidant trace elements?

Zinc

Zn is required for the preservation of the structural integrity of more than 2000 transcription factors and 300 enzymes(Reference Coleman62). Although the binding of Zn to many proteins is determinant for their function, three key signalling processes seem to be significant targets of a deficiency in Zn: the activation of NF-κB, the activation of caspase enzymes and NO signalling. Zn can stabilise membranes and is bound to protein thiol (-SH) groups protecting them from oxidation(Reference Xia, Browning and O'Dell63). Zn is mainly contained in meat, liver, eggs, seafood and, in a lower concentration, in dairy products and cereals. Because the intestinal absorption of Zn depends on its form and on the presence of either facilitating (lactose) or inhibiting (Cu2+, Fe2+, phytates, Ca2+) molecules, Zn bioavailability depends on the food from which it comes(Reference Hunt64). Plasma Zn concentrations can drop (by 50%) due to a restricted Zn absorption(Reference Cousins65). Excretion of Zn in faeces of the non-absorbed Zn fraction, intestinal desquamation, as well as digestive secretions, represents 10 mg/d. The main vector of Zn loss in athletes is sweat, reaching 5 mg/d when sweating is abundant. After 2 h of aerobic exercise, losses can represent respectively 9 and 8% of Zn RDA for men and women respectively(Reference DeRuisseau, Cheuvront, Haymes and Sharp66). Urinary loss is very low (0·3 to 0·6 mg/d). A regulation of this way of excretion does not compensate any loss by sweating(Reference Anderson, Bryden, Polansky and Deuster67). Moreover, Zn loss can be greater (up to 2 mg/d) in athletes because of proteinuria which may be induced by muscle damage due to intensive physical exercise.

Plasma concentrations have to range between 12 and 18 μmol/l. There is evidence of a marginal Zn status ( < 10·7 μmol/l) in 21% of athletes which could not be explained by their daily energy expenditure(Reference Margaritis, Rousseau, Hininger, Palazzetti, Arnaud and Roussel68). Semi-vegetarianism (exclusion of red meat) increases the prevalence of inadequate Zn status. This behaviour is frequently shown in female athletes with consequences on Zn status being reinforced due to an energy-restricted diet.

The more the subject undergoes training, the lower the plasma concentration of Zn is, and inversely, the less the subject undergoes training, the higher the plasma concentration of Zn is. This is proven in the case of interindividual approaches only(Reference Peake, Gerrard and Griffin69) and not in the case of intra-individual approaches(Reference Peake, Gerrard and Griffin69, Reference Dressendorfer, Petersen, Lovshin and Keen70). The concentration of erythrocyte Zn and metallothionein, a marker of the Zn reserve, is high in well-trained aerobic athletes(Reference Koury, de Olilveria, Portella, de Olilveria, Lopes and Donangelo71). This suggests that, in most cases, athletes are unlikely to benefit from Zn supplementation.

The increase in Zn demand due to physical activity is achieved by a well-balanced diet. If the necessity to increase Zn supplies is proven (long-lasting exercise in very hot environments could be the rare cases), it is of prime importance to pay attention to the ratio with Ca, Cu and Fe. Like other nutrients, Zn exhibits a U-shaped dose–response curve, with adverse health effects occurring when either too little or too much Zn is present in vulnerable tissues(Reference Slikker, Andersen and Bogdanffy72). In the case of excess, Zn supplies can provoke gastric dysfunction, dizziness, nausea and a vulnerability of the immune system. In France, the recommended dose is 10 mg/d, the no adverse effect level has been set at 30 mg/d and the increase in needs has been estimated to be 0·24 mg/1000 kJ (1 mg/1000 kcal) over sedentary energy expenditure. So, there is no benefit of high amounts of Zn supplementation. Performance is correlated with the plasma Zn concentration only in the case of Zn deficit. A high daily ingestion of Zn decreases the absorption of Cu and decreases the Cu status which, in turn, decreases the Cu-Zn-SOD enzyme activity. The major consequence associated with the long-term ingestion of moderately high amounts of Zn is the generation of a secondary Cu deficiency, which has been noticed with individuals having a chronic intake of Zn supplements as low as 50 mg/d(Reference Sandstead73).

Lack of evidence for increased needs for Zn with physical exercise does not lead us to propose a supplementary intake of up to 0·24 mg/1000 kJ (1 mg/1000 kcal) of energy expenditure which can be provided by a diversified diet.

Copper

Among the many functions of Cu, focus will be made here on its antioxidant function via the antioxidant activity of Cu-Zn-SOD. Cu is carried by ceruloplasmin – a non-enzymic antioxidant – but 60% of Cu is bound to erythrocyte Cu-Zn-SOD. A deficit in Cu, when combined with exercise, leads to an alteration of the basal laminae of myocardial cells and to a decrease in the oxidative capacity of the soleus muscle in rats(Reference Davidson, Medeiros, Hamlin and Jenkins74).

Losses of Cu through urine and sweat increase with exercise independently of the training level(Reference Anderson, Bryden, Polansky and Deuster67). Losses are lower when Cu intakes are low, preserving thus a minimal Cu bioavailability as well as the Cu-Zn-SOD activity. To date, no study has shown evidence of the values of plasma Cu concentrations below the normal rate in physically active subjects even in cases of high sweat loss or high energy expenditure. Water and energy supplies necessary for the compensation of these losses allow the maintenance of cupric balance. An average Cu intake of 1·96 mg/d is found in highly trained subjects (energy expenditure >16 740 kJ (4000 kcal)/d)(Reference Margaritis, Rousseau, Hininger, Palazzetti, Arnaud and Roussel68).

Plasma Cu concentrations increase in response to exercise and return to initial values within a few days(Reference Marrella, Guerrini, Solero, Tregnaghi, Schena and Velo75). Thus, basal concentrations of plasma Cu could be mainly due to previous exercise. The decrease in erythrocyte Cu concentrations in response to exercise(Reference Marrella, Guerrini, Solero, Tregnaghi, Schena and Velo75) suggests a mobilisation of Cu in response to exercise and could explain why plasma Cu concentrations are sometimes higher in athletes as compared with less active subjects. In fact, plasma Cu concentrations can increase during the training season, with a peak in concentrations after the competition period. Moreover, the activity of the erythrocyte Cu-Zn-SOD, one marker of Cu status, can vary with training loads(Reference Margaritis, Palazzetti, Rousseau, Richard and Favier76). In skeletal muscle, Cu-Zn-SOD activity is correlated with maximal O2 uptake values(Reference Jenkins, Friedland and Howald77). Athletes who most risk Cu deficit are those who take high-Fe or -Zn supplement doses and those with high-glycaemic index carbohydrate ingestion because of the antagonistic action of those compounds on Cu intestinal absorption(Reference Sandstead73, Reference Landes78).

Selenium

The essential trace mineral Se as required for the functionality of selenoproteins is of fundamental importance to human health(Reference Thomson79). Selenocysteine is incorporated in at least twenty-five specific, genetically determined human selenoproteins, many of which have only recently been discovered(Reference Kryukov, Castellano, Novoselov, Lobanov, Zehtab, Guigó and Gladyshev80). Among well-known selenoproteins, glutathione peroxidases (GSH-Px), thioredoxin reductase and methionine sulfoxide reductase B are involved in the antioxidant defences.

In cases of Se depletion, Se is taken from muscle, carried and possibly deposited in tissues with a higher metabolic priority for Se such as the testes, brain and endocrine organs(Reference Hawkes, Alkan and Oehler81, Reference Ji, Stratman and Lardy82). GSH-Px (isoform 1) protein concentration and activity are depleted in several tissues(Reference Ji, Stratman and Lardy82). Se depletion leads to a morphological myocardial myocyte alteration, as well as to a disorganisation of the mitochondrial membrane. Moreover, the combined depletion of both Se and glutathione induces necrosis of both kidney and liver tissues(Reference Burk, Hill, Awad, Morrow and Lyons83). Thiol groups contained in enzymes decrease with Se-deficient mice when subjected to an intensive training(Reference Soares, Folmer and Rocha84).

The bioavailability of Se seems to adapt when Se intakes are moderatly low or high. Faecal and urinary excretions decrease when the diet is poor in Se. Inversely, a readjustement in Se excretion is also observed along with an increase in urinary and faecal excretion when Se intakes are high(Reference Hawkes, Alkan and Oehler81). This regulation of excretion does not occur when intakes are above or below a certain threshold(Reference Hawkes, Alkan and Oehler81).

Plasma Se concentrations of 1·15 μmol/l are known to maximise erythrocyte GSH-Px activity, which is used as a functional marker of Se status(Reference Thomson79). Some athletes exhibited plasma Se concentrations below this concentration(Reference Margaritis, Rousseau, Hininger, Palazzetti, Arnaud and Roussel68). However, most of highly and well-trained athletes generally adopt a high-Se diet spontaneously, which allows them to reach a high Se status(Reference Margaritis, Rousseau, Hininger, Palazzetti, Arnaud and Roussel68). The biological efficiency of Se in humans depends on the food source. It is therefore legitimate to question the nutritional Se density of athletes' diet but also to question the quality of the dietary sources. In healthy subjects, 39 % of Se is linked to plasma GSH-Px (isoform 3), 53 % to selenoprotein P and 9 % to albumin. Selenomethionine is mainly found in albumin. This Se distribution consequently varies according to the quality and to the quantity of dietary intakes(Reference Deagen, Butler, Zachara and Whanger85). Most of the Se in vegetables is in the form of selenomethionine whereas selenocysteine, which is used for selenoprotein synthesis, is mainly of animal food origin(Reference Thomson79). Se is also present in the form of selenite and selenate in food, both of which are also used for selenoprotein synthesis. As the percentage of plant protein supplies is higher in well-trained athletes in comparison with less trained athletes(Reference Margaritis, Rousseau, Hininger, Palazzetti, Arnaud and Roussel68), Se supply coming from foods – of plant origin – rich in carbohydrates will be higher in the form of selenomethionine. The selenomethionine can be incorporated randomly in proteins instead of methionine. The part of non-metabolised selenomethionine is incorporated into tissues undergoing high protein turnover such as skeletal muscle and erythrocytes. Training introduces additional factors which induce an endogenous adaptive response of GSH-Px activity, probably mostly at post-translational level(Reference Rousseau, Margaritis, Arnaud, Faure and Roussel44, Reference Drăgan, Dinu, Mohora, Cristea, Ploeşteanu and Stroescu86). Factors such as ageing, sex or hypoxia exposure are also known to increase erythrocyte and/or plasma GSH-Px activity(Reference Rousseau, Margaritis, Arnaud, Faure and Roussel44, Reference Ha and Smith87, Reference Rousseau, Richer, Richard, Favier and Margaritis88). Therefore, the dose–response association between plasma Se concentrations and the erythrocyte GSH-Px activity is not always evidenced in athletes(Reference Rousseau, Margaritis, Arnaud, Faure and Roussel44, Reference Margaritis, Rousseau, Hininger, Palazzetti, Arnaud and Roussel68). This raises the question of the validity of circulating GSH-Px activity as a Se status indicator in a training population.

With top-level athletes, Se supplementation with daily doses taken of 50 or 100 μg at once or in several intakes decreases lipid peroxidation and increases non-protein thiol groups(Reference Drăgan, Dinu, Mohora, Cristea, Ploeşteanu and Stroescu86). However, others reported no effect of a daily supplementation (180 μg selenomethionine) during a 10-week training period with subjects originally less active on oxidative stress markers and on erythrocyte and muscle GSH-Px activities(Reference Tessier, Margaritis, Richard, Moynot and Marconnet89).

The increase in Se requirements with physical exercise is probably not linear(Reference Margaritis, Rousseau, Hininger, Palazzetti, Arnaud and Roussel68). The effect of the form of Se ingested (selenomethionine, selenocysteine, selenite, selenate) should be investigated as well as the effect of Se on other selenoproteins' functions. Data relating to the long-term effects of Se complements and supplements are lacking. A safety dose of 150 μg Se/d has nevertheless been suggested in France.

Is antioxidant micronutrient supplementation to be encouraged or discouraged?

Paradoxically, individuals who take supplements are generally those with the healthiest quality of life (non-smokers, with well-controlled physical activity programmes, etc) and whose fruit and vegetable consumption is high. Moreover, athletes who practise long-lasting activities often eat fortified foods. One can suppose that some athletes ingest more than they need. An excess of one antioxidant through supplementation could fail to provide a full antioxidant protection. It could also reduce the adaptive effect of the endogenous antioxidant system induced by physical training by minimising the effects of ROS themselves. These last play a major role in the signalling mechanisms that trigger the expression of antioxidant enzymes(Reference Dressendorfer, Petersen, Lovshin and Keen70). High doses of antioxidant supplementation have been shown several times to delay the exercise-induced stress protein increase and therefore the muscle homeostasis return. It seems that maintaining a normal antioxidant status through dietary intakes is essential in the adaptation process.

Exercise-induced oxidative damage can be alleviated by endogenous antioxidant adaptation. Antioxidant intakes determine the quality of the endogenous antioxidant system response(Reference Gomez-Cabrera, Domenech, Romagnoli, Arduini, Borras, Pallardo, Sastre and Viña19). The latter is dependent on training habits. In stable physiological conditions and with a reasoned choice of training loads, endogenous antioxidant system adaptation is proportionnal to training load. However, below and above a stimulation threshold triggered by a given load, the relationship between training loads and endogenous adaptation is not verified(Reference Margaritis, Palazzetti, Rousseau, Richard and Favier76, Reference Palazzetti, Richard, Favier and Margaritis90). An interdependence of antioxidant intakes and the effects of training on the endogenous antioxidant system has been observed in reference to a training-load modulation (increase/decrease)(Reference Palazzetti, Rousseau, Richard, Favier and Margaritis7, Reference Margaritis, Palazzetti, Rousseau, Richard and Favier76). This supposes that the antioxidants required during a period of increased or reduced training stress differ from those required during a ‘normal’ training period. Before a major competition, a training-load modulation (overloading/tapering), with initially well-adapted subjects, is a common strategy to reach a performance peak when the competition comes. Overloading is known to provoke a transitory or prolonged lack of physiological and/or biochemical adaptations. Endogenous antioxidant systems are not able to counteract the excess of ROS produced and oxidative stress is generated(Reference Palazzetti, Richard, Favier and Margaritis90). The maintenance of a normal nutritional status is determinant. If the effects of a supplementation during overtraining are mostly evident in the lessening of muscle damage, it is noteworthy that the supplied doses can be provided by a diversified and well-balanced diet(Reference Palazzetti, Rousseau, Richard, Favier and Margaritis7). The effects of antioxidant supplements are mainly visible when subjects are initially deficient in antioxidants or when the food ingested is limited in the given antioxidants(Reference Mastaloudis, Morrow, Hopkins, Devaraj and Traber91, Reference Watson, Callister, Taylor, Sibbritt, MacDonald-Wicks and Garg92). Such a deficit is also visible in some subjects during the overloaded period of training. Available data still do not allow us to define the optimal antioxidant intakes that would protect overloaded or, even more so, overtrained subjects.

The intricate relationship between exogenous antioxidant intakes and training effects requires the linking of the interpretation of biological data to each individual case. In fact, the specificity of the adaptive response is the function of individual factors such as the training period, the type of physical activity performed, the training level, the age of the subjects, the environmental conditions and the infinite interindividual differences. In specific, identified cases, an antioxidant complex could help athletes with initially low antioxidant intakes to maintain their antioxidant status during an overloaded period of training.

Do data have a biological significance?

Beyond the limited relevance of the numerous markers, the statistical significance of changes in a result does not obviously mean that it has a biological significance. The variations seen during experimentation are transitory when exposure to stress is transitory. The reading of experimental results allows us only to guess the middle- or long-term effects of these complements or supplements.

The plasma concentration of fat-soluble micronutrients such as α-tocopherol and carotenoids may depend on the expression level of gene coding for proteins strongly involved in the metabolism of lipids such as those activated by peroxisome proliferated activated receptors. The latter's level of expression, with regards particularly to isoform β/δ, varies with physical exercise(Reference Grimaldi93). Nucleotide polymorphisms on these genes may, on the other hand, provide an answer to the strong inter-individual variations of plasma α-tocopherol and carotenoid concentrations(Reference Rousseau, Hininger, Palazzetti, Faure, Roussel and Margaritis6, Reference Rousseau, Margaritis, Arnaud, Faure and Roussel44). To this effect, a recent study showed that the presence of single nucleotide polymorphisms on the gene of SR-BI strongly influenced the concentrations of α-tocopherol and β-carotene(Reference Borel, Moussa and Reboul25). However, as of date, the effect of physical exercise on the level of expression of this receptor is not yet known.

The clinician can rely on the RDA for the general and the specific population. He also has to pay particular attention to subjects with an atypical profile and keep an individualised approach.

The choice of markers depends on the function affected by the exercise and/or by the deficit of the nutrient intake (for example GSH-Px activity for Se status). With exercise, the biological data can only vary in a transitory manner because of a transfer from one compartment to another. The continuous evolution and increase in available markers would further help both researchers and clinicians to evaluate more precisely nutritional status.

The quality of the food composition table for trace elements, carotenoids and flavonoids is still considered to be poor. Moreover, quantities of nutrients within food vary among countries and studies are not always comparable. Due to the variability of trace elements in soils, especially in Se, and to the consequent variability of their content in the identical food, conventional methods to estimate Se intakes are not always adequate. Food diaries or questionnaires are often validated for a sedentary population and consequently need to be adapted and validated in a population of athletes. In fact, a limit of these questionnaires could be the underestimation of food intake by athletes due to large portion sizes. Another limit could be linked to the reporting of portion sizes by some subjects, mostly women, all the more in sports which have an aesthetic component. Thus, the dietary approach needs to be completed by a biological assessment. Considering the limits of the reliability of biological assessments and dietary surveys, mainly in athletic populations, only a full nutritional assessment including both a dietary survey and a biological assessment can lead to suggest to athletes, in particular conditions, complements to compensate for deficits. In cases in which the intakes are below the recommended intake level, the supplementation can become a ‘complementation’. An enriched diet, with the same aim, could have similar effects.

Conclusion

Athletes are seeking methods to improve performance. Among those methods is the nutritional strategy. Low intakes can alter performance, as adequate intakes play a protective role. In this case, the dietary nutritional addition is only done with the goal of reaching an appropriate nutritional status and to restore biochemical and physiological functions using specifically chosen biomarkers. The long-term risks of deficiency, as well as excessive intakes of antioxidant micronutrients, are still unknown because they are still poorly investigated in athletes. A recent meta-analysis showed that antioxidant supplements, with the evoked exception of Se, may increase all-cause mortality(Reference Bjelakovic, Nikolova, Gluud, Simonetti and Gluud94). The numerous studies carried out on antioxidant supplementation encourage caution as long as longitudinal studies in athletes do not allow the discarding of the hypothesis of antioxidant supplementation-linked risk.

High-training-stress periods are key periods for nutritional awareness. In most cases, the nutritional risk of deficit can be reduced by a rational application of recommended training loads and requirement can be satisfied by a well-balanced diet.

The authors declare that they have no conflicts of interest.

References

1Wilson, JX (2002) The physiological role of dehydroascorbic acid. FEBS Lett 527, 59.CrossRefGoogle ScholarPubMed
2Levine, M, Wang, Y, Padayatty, SJ & Morrow, JA (2001) A new recommended dietary allowance of vitamin C for healthy young women. Proc Natl Acad Sci U S A 98, 98429846.Google Scholar
3Bergholm, R, Mäkimattila, S, Valkonen, M, Liu, ML, Lahdenperä, S, Taskinen, MR, Sovijärvi, A, Malmberg, P & Yki-Järvinen, H (1999) Intense physical training decreases circulating antioxidants and endothelium-dependent vasodilatation in vivo. Atherosclerosis 145, 341349.Google Scholar
4Pincemail, J, Lecomte, J, Castiau, J, Collard, E, Vasankari, T, Cheramy-Bien, J, Limet, R & Defraigne, J (2000) Evaluation of autoantibodies against oxidized LDL and antioxidant status in top soccer and basketball players after 4 months of competition. Free Radic Biol Med 28, 559565.CrossRefGoogle ScholarPubMed
5Schröder, H, Navarro, E, Tramullas, A, Mora, J & Galiano, D (2000) Nutrition antioxidant status and oxidative stress in professional basketball players: effects of a three compound antioxidative supplement. Int J Sports Med 21, 146150.CrossRefGoogle ScholarPubMed
6Rousseau, AS, Hininger, I, Palazzetti, S, Faure, H, Roussel, AM & Margaritis, I (2004) Antioxidant vitamin status in high exposure to oxidative stress in competitive athletes. Br J Nutr 92, 461468.Google Scholar
7Palazzetti, S, Rousseau, AS, Richard, MJ, Favier, A & Margaritis, I (2004) Antioxidant supplementation preserves antioxidant response in physical training and low antioxidant intake. Br J Nutr 91, 91100.Google Scholar
8Cazzola, R, Russo-Volpe, S, Cervato, G & Cstaro, B (2003) Biochemical assessments of oxidative stress, erythrocyte membrane fluidity and antioxidant status in professional soccer players and sedentary controls. Eur J Clin Invest 33, 924930.CrossRefGoogle ScholarPubMed
9Evelson, P, Gambino, G, Travacio, M, Jaita, G, Verona, J, Maroncelli, C, Wikinski, R, Llesuy, S & Brites, F (2002) Higher antioxidant defences in plasma and low density lipoproteins from rugby players. Eur J Clin Invest 32, 818825.Google Scholar
10Kanter, MM, Nolte, LA & Holloszy, JO (1993) Effects of an antioxidant vitamin mixture on lipid peroxidation at rest and postexercise. J Appl Physiol 74, 965969.CrossRefGoogle ScholarPubMed
11Telford, RD, Catchpole, EA, Deakin, V, McLeay, AC & Plank, AW (1992) The effect of 7 to 8 months of vitamin/mineral supplementation on the vitamin and mineral status of athletes. Int J Sport Nutr 2, 123134.CrossRefGoogle ScholarPubMed
12Podmore, ID, Griffiths, HR, Herbert, KE, Mistry, N, Mistry, P & Lunec, J (1998) Vitamin C exhibits pro-oxidant properties. Nature 392, 559.Google Scholar
13Bryant, RJ, Ryder, J, Martino, P, Kim, J & Craig, BW (2003) Effects of vitamin E and C supplementation either alone or in combination on exercise-induced lipid peroxidation in trained cyclists. J Strength Cond Res 17, 792800.Google Scholar
14Childs, A, Jacobs, C, Kaminski, T, Halliwell, B & Leeuwenburgh, C (2001) Supplementation with vitamin C and N-acetyl-cysteine increases oxidative stress in humans after an acute muscle injury induced by eccentric exercise. Free Radic Biol Med 31, 745753.Google Scholar
15Sandström, B (2001) Micronutrient interactions: effects on absorption and bioavailability. Br J Nutr 85, Suppl. 2, 181S185S.Google Scholar
16Zoller, H & Vogel, W (2004) Iron supplementation in athletes – first do no harm. Nutrition 20, 615619.Google Scholar
17Hemila, H (2006) The effect of nutrition on exercise-induced immunodepression. Nutr Rev 64, 476477.Google Scholar
18Moreira, A, Kekkonen, RA, Delgado, L, Fonseca, J, Korpela, R & Haahtela, T (2007) Nutritional modulation of exercise-induced immunodepression in athletes: a systematic review and meta-analysis. Eur J Clin Nutr 61, 443460.Google Scholar
19Gomez-Cabrera, MC, Domenech, E, Romagnoli, M, Arduini, A, Borras, C, Pallardo, FV, Sastre, J & Viña, J (2008) Oral administration of vitamin C decreases muscle mitochondrial biogenesis and hampers training-induced adaptations in endurance performance. Am J Clin Nutr 87, 142149.CrossRefGoogle ScholarPubMed
20St-Pierre, J, Drori, S, Uldry, M, et al. . (2006) Suppression of reactive oxygen species and neurodegeneration by the PGC-1 transcriptional coactivators. Cell 127, 397408.CrossRefGoogle ScholarPubMed
21Khassaf, M, McArdle, A, Esanu, C, Vasilaki, A, McArdle, F, Griffiths, RD, Brodie, DA & Jackson, MJ (2003) Effect of vitamin C supplements on antioxidant defence and stress proteins in human lymphocytes and skeletal muscle. J Physiol 549, 645652.CrossRefGoogle ScholarPubMed
22Close, GL, Ashton, T, Cable, T, Doran, D, Holloway, C, McArdle, F & MacLaren, DP (2006) Ascorbic acid supplementation does not attenuate post-exercise muscle soreness following muscle-damaging exercise but may delay the recovery process. Br J Nutr 95, 976981.CrossRefGoogle Scholar
23Coombes, JS, Rowell, B, Dodd, SL, Demirel, HA, Naito, H, Shanely, RA & Powers, SK (2002) Effects of vitamin E deficiency on fatigue and muscle contractile properties. Eur J Appl Physiol 87, 272277.CrossRefGoogle ScholarPubMed
24Mardones, P & Rigotti, A (2004) Cellular mechanisms of vitamin E uptake: relevance in α-tocopherol metabolism and potential implications for disease. J Nutr Biochem 15, 252260.CrossRefGoogle ScholarPubMed
25Borel, P, Moussa, M, Reboul, E, et al. . (2007) Human plasma levels of vitamin E and carotenoids are associated with genetic polymorphisms in genes involved in lipid metabolism. J Nutr 137, 26532659.CrossRefGoogle ScholarPubMed
26Aguiló, A, Tauler, P, Pilar Guix, M, Villa, G, Córdova, A, Tur, JA & Pons, A (2003) Effect of exercise intensity and training on antioxidants and cholesterol profile in cyclists. J Nutr Biochem 14, 319325.CrossRefGoogle ScholarPubMed
27Pincemail, J, Deby, C, Camus, G, Pirnay, F, Bouchez, R, Massaux, L & Goutier, R (1988) Tocopherol mobilization during intensive exercise. Eur J Appl Physiol Occup Physiol 57, 189191.CrossRefGoogle ScholarPubMed
28Okamura, K, Doi, T, Hamada, K, Sakurai, M, Yoshioka, Y, Mitsuzono, R, Migita, T, Sumida, S & Sugawa-Katayama, Y (1997) Effect of repeated exercise on urinary 8-hydroxy-deoxyguanosine excretion in humans. Free Radic Res 26, 507514.Google Scholar
29Mastaloudis, A, Leonard, SW & Traber, MG (2001) Oxidative stress in athletes during extreme endurance exercise. Free Radic Biol Med 31, 911922.Google Scholar
30Tiidus, PM (2000) Estrogen and gender effects on muscle damage, inflammation, and oxidative stress. Can J Appl Physiol 25, 274287.Google Scholar
31Tiidus, PM, Behrens, WA, Madere, R & Houston, ME (1993) Muscle vitamin E levels following acute submaximal exercise in female rats. Acta Physiol Scand 147, 249250.CrossRefGoogle ScholarPubMed
32Kelly, DA, Tiidus, PM, Houston, ME & Noble, EG (1996) Effect of vitamin E deprivation and exercise training on induction of HSP70. J Appl Physiol 81, 23792385.Google Scholar
33Hartmann, A, Niess, AM, Grunert-Fuchs, M, Poch, B & Speit, G (1995) Vitamin E prevents exercise-induced DNA damage. Mutat Res 346, 195202.Google Scholar
34Meydani, M, Evans, WJ, Handelman, G, Biddle, L, Fielding, RA, Meydani, SN, Burrill, J, Fiatarone, MA, Blumberg, JB & Cannon, JG (1993) Protective effect of vitamin E on exercise-induced oxidative damage in young and older adults. Am J Physiol 264, R992R998.Google ScholarPubMed
35Rokitzki, L, Logemann, E, Huber, G, Keck, E & Keul, J (1994) α-Tocopherol supplementation in racing cyclists during extreme endurance training. Int J Sport Nutr 4, 253264.Google Scholar
36Buchman, AL, Killip, D, Ou, CN, Rognerud, CL, Pownall, H, Dennis, K & Dunn, JK (1999) Short-term vitamin E supplementation before marathon running: a placebo-controlled trial. Nutrition 15, 278283.Google Scholar
37Witt, W, Kolleck, I, Fechner, H, Sinha, P & Rustow, B (2000) Regulation by vitamin E of the scavenger receptor BI in rat liver and HepG2 cells. J Lipid Res 41, 20092016.CrossRefGoogle ScholarPubMed
38McAnulty, SR, McAnulty, LS, McAnulty, LS, Nieman, DC, Morrow, JD, Shooter, LA, Holmes, S, Heward, C & Henson, DA (2005) Effect of α-tocopherol supplementation on plasma homocysteine and oxidative stress in highly trained athletes before and after exhaustive exercise. J Nutr Biochem 16, 530537.CrossRefGoogle ScholarPubMed
39Nieman, DC, Henson, DA, McAnulty, SR, McAnulty, LS, Morrow, JD, Ahmed, A & Heward, CB (2004) Vitamin E and immunity after the Kona Triathlon World Championship. Med Sci Sports Exerc 36, 13281335.CrossRefGoogle ScholarPubMed
40Herrera, E & Barbas, C (2001) Vitamin E: action, metabolism and perspectives. J Physiol Biochem 57, 4356.CrossRefGoogle Scholar
41Krinsky, NI & Yeum, KJ (2003) Carotenoid-radical interactions. Biochem Biophys Res Commun 305, 754760.Google Scholar
42van het Hof, KH, Brouwer, IA, West, CE, Haddeman, E, Steegers-Theunissen, RP, van Dusseldorp, M, Weststrate, JA, Eskes, TK & Hautvast, JG (1999) Bioavailability of lutein from vegetables is 5 times higher than that of β-carotene. Am J Clin Nutr 70, 261268.Google Scholar
43Sumida, S, Doi, T, Sakurai, M, Yoshioka, Y & Okamura, K (1997) Effect of a single bout of exercise and β-carotene supplementation on the urinary excretion of 8-hydroxy-deoxyguanosine in humans. Free Radic Res 27, 607618.Google Scholar
44Rousseau, AS, Margaritis, I, Arnaud, J, Faure, H & Roussel, AM (2006) Physical activity alters antioxidant status in exercising elderly subjects. J Nutr Biochem 17, 463470.Google Scholar
45Schmidt, MC, Askew, EW, Roberts, DE, Prior, RL, Ensign, WY Jr & Hesslink, RE Jr (2002) Oxidative stress in humans training in a cold, moderate altitude environment and their response to a phytochemical antioxidant supplement. Wilderness Environ Med 13, 94105.Google Scholar
46Kontush, A, Weber, W & Beisiegel, U (2000) Alpha- and beta-carotenes in low density lipoprotein are the preferred target for nitric oxide-induced oxidation. Atherosclerosis 148, 8793.CrossRefGoogle ScholarPubMed
47Niki, E, Noguchi, N, Tsuchihashi, H & Gotoh, N (1995) Interaction among vitamin C, vitamin E, and β-carotene. Am J Clin Nutr 62, Suppl. 6, 1322S1326S.Google Scholar
48Chen, CY, Milbury, PE, Lapsley, K & Blumberg, JB (2005) Flavonoids from almond skins are bioavailable and act synergistically with vitamins C and E to enhance hamster and human LDL resistance to oxidation. J Nutr 135, 13661373.CrossRefGoogle Scholar
49Ameho, CK, Chen, CY, Smith, D, Sanchez-Moreno, C, Milbury, PE & Blumberg, JB (2008) Antioxidant activity and metabolite profile of quercetin in vitamin-E-depleted rats. J Nutr Biochem 19, 467474.CrossRefGoogle ScholarPubMed
50Klotz, LO & Sies, H (2003) Defenses against peroxynitrite: selenocompounds and flavonoids. Toxicol Lett 140, 125132.Google Scholar
51Ruiz-Larrea, MB, Mohan, AR, Paganga, G, Miller, NJ, Bolwell, GP & Rice-Evans, CA (1997) Antioxidant activity of phytoestrogenic isoflavones. Free Radic Res 26, 6370.Google Scholar
52Viña, J, Sastre, J, Pallardó, FV, Gambini, J & Borrás, C (2008) Modulation of longevity-associated genes by estrogens or phytoestrogens. Biol Chem 389, 273277.Google Scholar
53de Vries, JH, Hollman, PC, Meyboom, S, Buysman, MN, Zock, PL, van Staveren, WA & Katan, MB (1998) Plasma concentrations and urinary excretion of the antioxidant flavonols quercetin and kaempferol as biomarkers for dietary intake. Am J Clin Nutr 68, 6065.Google Scholar
54Panza, VS, Wazlawik, E, Ricardo Schutz, G, Comin, L, Hecht, KC & da Silva, EL (2008) Consumption of green tea favorably affects oxidative stress markers in weight-trained men. Nutrition 24, 433442.CrossRefGoogle ScholarPubMed
55Nieman, DC, Henson, DA, Davis, JM, et al. . (2007) Quercetin's influence on exercise-induced changes in plasma cytokines and muscle and leukocyte cytokine mRNA. J Appl Physiol 103, 17281735.CrossRefGoogle ScholarPubMed
56McAnulty, SR, McAnulty, LS, Nieman, DC, et al. . (2008) Chronic quercetin ingestion and exercise-induced oxidative damage and inflammation. Appl Physiol Nutr Metab 33, 254262.CrossRefGoogle ScholarPubMed
57Nieman, DC, Henson, DA, Gross, SJ, et al. . (2007) Quercetin reduces illness but not immune perturbations after intensive exercise. Med Sci Sports Exerc 39, 15611569.CrossRefGoogle Scholar
58Duthie, SJ, Johnson, W & Dobson, VL (1997) The effect of dietary flavonoids on DNA damage (strand breaks and oxidised pyrimdines) and growth in human cells. Mutat Res 390, 141151.CrossRefGoogle ScholarPubMed
59Hurrell, RF, Reddy, M & Cook, JD (1999) Inhibition of non-haem iron absorption in man by polyphenolic-containing beverages. Br J Nutr 81, 289295.Google Scholar
60Chun, OK, Chung, SJ, Claycombe, KJ & Song, WO (2008) Serum C-reactive protein concentrations are inversely associated with dietary flavonoid intake in U.S. adults. J Nutr 138, 753760.Google Scholar
61Williamson, G & Manach, C (2005) Bioavailability and bioefficacy of polyphenols in humans. II. Review of 93 intervention studies. Am J Clin Nutr 81, Suppl. 1, 243S255S.Google Scholar
62Coleman, JE (1992) Zinc proteins: enzymes, storage proteins, transcription factors, and replication proteins. Annu Rev Biochem 61, 897946.Google Scholar
63Xia, J, Browning, JD & O'Dell, BL (1999) Decreased plasma membrane thiol concentration is associated with increased osmotic fragility of erythrocytes in zinc-deficient rats. J Nutr 129, 814819.CrossRefGoogle ScholarPubMed
64Hunt, JR (2003) Bioavailability of iron, zinc, and other trace minerals from vegetarian diets. Am J Clin Nutr 78, Suppl. 3, 633S639S.Google Scholar
65Cousins, RJ (1989) Theoretical and practical aspects of zinc uptake and absorption. Adv Exp Med Biol 249, 312.CrossRefGoogle ScholarPubMed
66DeRuisseau, KC, Cheuvront, SN, Haymes, EM & Sharp, RG (2002) Sweat iron and zinc losses during prolonged exercise. Int J Sport Nutr Exerc Metab 12, 428437.CrossRefGoogle ScholarPubMed
67Anderson, RA, Bryden, NA, Polansky, MM & Deuster, PA (1995) Acute exercise effects on urinary losses and serum concentrations of copper and zinc of moderately trained and untrained men consuming a controlled diet. Analyst 120, 867870.Google Scholar
68Margaritis, I, Rousseau, AS, Hininger, I, Palazzetti, S, Arnaud, J & Roussel, AM (2005) Increase in selenium requirements with physical activity loads in well-trained athletes is not linear. Biofactors 23, 4555.Google Scholar
69Peake, JM, Gerrard, DF & Griffin, JF (2003) Plasma zinc and immune markers in runners in response to a moderate increase in training volume. Int J Sports Med 24, 212216.Google Scholar
70Dressendorfer, RH, Petersen, SR, Lovshin, SE & Keen, CL (2002) Mineral metabolism in male cyclists during high-intensity endurance training. Int J Sport Nutr Exerc Metab 2, 6372.CrossRefGoogle Scholar
71Koury, JC, de Olilveria, AV Jr, Portella, ES, de Olilveria, CF, Lopes, GC & Donangelo, CM (2004) Zinc and copper biochemical indices of antioxidant status in elite athletes of different modalities. Int J Sport Nutr Exerc Metab 14, 358372.Google Scholar
72Slikker, W Jr, Andersen, ME, Bogdanffy, MS, et al. . (2004) Dose-dependent transitions in mechanisms of toxicity. Toxicol Appl Pharmacol 201, 203225.Google Scholar
73Sandstead, HH (1995) Requirements and toxicity of essential trace elements, illustrated by zinc and copper. Am J Clin Nutr 61, Suppl. 3, 621S624S.CrossRefGoogle ScholarPubMed
74Davidson, J, Medeiros, DM, Hamlin, RL & Jenkins, JE (1993) Submaximal, aerobic exercise training exacerbates the cardiomyopathy of postweanling Cu-depleted rats. Biol Trace Elem Res 38, 251272.Google Scholar
75Marrella, MF, Guerrini, F, Solero, PL, Tregnaghi, PL, Schena, F & Velo, GP (1993) Blood copper and zinc changes in runners after a marathon. J Trace Elem Electrolytes Health Dis 7, 248250.Google Scholar
76Margaritis, I, Palazzetti, S, Rousseau, AS, Richard, MJ & Favier, A (2003) Antioxidant supplementation and tapering exercise improve exercise-induced antioxidant response. J Am Coll Nutr 22, 147156.Google Scholar
77Jenkins, RR, Friedland, R & Howald, H (1984) The relationship of oxygen uptake to superoxide dismutase and catalase activity in human skeletal muscle. Int J Sports Med 5, 1114.Google Scholar
78Landes, DR (1975) Influence of dietary carbohydrate on copper, iron, and zinc status of the rat. Proc Soc Exp Biol Med 150, 686689.Google Scholar
79Thomson, CD (2004) Assessment of requirements for selenium and adequacy of selenium status: a review. Eur J Clin Nutr 58, 391402.Google Scholar
80Kryukov, GV, Castellano, S, Novoselov, SV, Lobanov, AV, Zehtab, O, Guigó, R & Gladyshev, VN (2003) Characterization of mammalian selenoproteomes. Science 300, 14391443.Google Scholar
81Hawkes, WC, Alkan, FZ & Oehler, L (2003) Absorption, distribution and excretion of selenium from beef and rice in healthy North American men. J Nutr 133, 34343442.Google Scholar
82Ji, LL, Stratman, FW & Lardy, HA (1988) Antioxidant enzyme systems in rat liver and skeletal muscle. Influences of selenium deficiency, chronic training, and acute exercise. Arch Biochem Biophys 263, 150160.Google Scholar
83Burk, RF, Hill, KE, Awad, JA, Morrow, JD & Lyons, PR (1995) Liver and kidney necrosis in selenium-deficient rats depleted of glutathione. Lab Invest 72, 723730.Google Scholar
84Soares, JC, Folmer, V & Rocha, JB (2003) Influence of dietary selenium supplementation and exercise on thiol-containing enzymes in mice. Nutrition 19, 627632.CrossRefGoogle ScholarPubMed
85Deagen, JT, Butler, JA, Zachara, BA & Whanger, PD (1993) Determination of the distribution of selenium between glutathione peroxidase, selenoprotein P, and albumin in plasma. Anal Biochem 208, 176181.Google Scholar
86Drăgan, I, Dinu, V, Mohora, M, Cristea, E, Ploeşteanu, E & Stroescu, V (1990) Studies regarding the antioxidant effects of selenium on top swimmers. Rev Roum Physiol 27, 1520.Google Scholar
87Ha, EJ & Smith, AM (2003) Plasma selenium and plasma and erythrocyte glutathione peroxidase activity increase with estrogen during the menstrual cycle. J Am Coll Nutr 22, 4351.Google Scholar
88Rousseau, AS, Richer, C, Richard, MJ, Favier, A & Margaritis, I (2006) Plasma glutathione peroxidase activity as a potential indicator of hypoxic stress in breath-hold diving. Aviat Space Environ Med 77, 551555.Google Scholar
89Tessier, F, Margaritis, I, Richard, MJ, Moynot, C & Marconnet, P (1995) Selenium and training effects on the glutathione system and aerobic performance. Med Sci Sports Exerc 27, 390396.Google Scholar
90Palazzetti, S, Richard, MJ, Favier, A & Margaritis, I (2003) Overloaded training increases exercise-induced oxidative stress and damage. Can J Appl Physiol 28, 588604.Google Scholar
91Mastaloudis, A, Morrow, JD, Hopkins, DW, Devaraj, S & Traber, MG (2004) Antioxidant supplementation prevents exercise-induced lipid peroxidation, but not inflammation, in ultramarathon runners. Free Radic Biol Med 36, 13291341.Google Scholar
92Watson, TA, Callister, R, Taylor, R, Sibbritt, D, MacDonald-Wicks, LK & Garg, ML (2003) Antioxidant restricted diet increases oxidative stress during acute exhaustive exercise. Asia Pac J Clin Nutr, Suppl. 12, S9.Google Scholar
93Grimaldi, PA (2007) Regulatory functions of PPARβ in metabolism: implications for the treatment of metabolic syndrome. Biochim Biophys Acta 1771, 983990.Google Scholar
94Bjelakovic, GD, Nikolova, LL, Gluud, RG, Simonetti, RG & Gluud, C (2007) Mortality in randomized trials of antioxidant supplements for primary and secondary prevention: systematic review and meta-analysis. JAMA 297, 842857.Google Scholar