Intake of specific flavonoids and risk of acute myocardial infarction in Italy

Alessandra Tavani^{1, CA1}, Luana Spertini¹, Cristina Bosetti¹, Maria Parpinel², Patrizia Gnagnarella³, Francesca Bravi¹, Julie Peterson⁴, Johanna Dwyer⁵, Pagona Lagiou⁶, Eva Negri¹, Carlo La Vecchia^1,7
1Istituto di Ricerche Farmacologiche ‘Mario Negri’, Via Eritrea 62, I-20157 , Milan, Italy
²Istituto di Igiene, Università di Udine, Udine, Italy
³Divisione di Epidemiologia e Biostatistica, Istituto Europeo di Oncologia, Milan, Italy
⁴Frances Stern Nutrition Center, Tufts–New England Medical Center, Boston, MA, USA
⁵Schools of Medicine, Nutrition and the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, Boston, MA, USA
⁶Department of Hygiene and Epidemiology, University of Athens Medical School, Athens, Greece
⁷Istituto di Statistica Medica e Biometria, Università degli Studi di Milano, Milan, Italy

10 May 2005 - 10 August 2005 - Submitted 10 May 2005:

Abstract

Objective: As intake of flavonoids has been associated with reduced risk of coronary heart disease but data on the relation with specific classes of flavonoids are scarce, we assessed the relation between dietary intake of specific classes of flavonoids and the risk of acute myocardial infarction (AMI) in an Italian population.

Design: Case–control study. Dietary information was collected by interviewers on a questionnaire tested for validity and reproducibility. Adjusted odds ratios (OR) and 95% confidence intervals (CI) were obtained by multiple logistic regression models including terms for energy and alcohol intake, as well as sociodemographic factors, tobacco and other major recognised risk factors for AMI.

Setting: Milan, Italy, between 1995 and 2003.

Subjects: Cases were 760 patients, below age 79 years, with a first episode of non-fatal AMI, and controls were 682 patients admitted to hospital for acute conditions unrelated to diet.

Results: A reduced risk of AMI was found for increasing intake of anthocyanidins (OR=0.45, 95% CI 0.26–0.78 for the highest vs. the lowest quintile, P_trend=0.003) and flavonols (OR=0.65, 95% CI 0.41–1.02, P_trend=0.02). A tendency towards reduced risks, although not significant, was observed for flavan-3-ols (OR=0.73, 95% CI 0.48–1.10) and total flavonoids (OR=0.74, 95% CI 0.49–1.14). No meaningful heterogeneity was found between the sexes. No association emerged for other flavonoids, including isoflavones, flavanones and flavones.

Conclusions: High intake of anthocyanidins reduced the risk of AMI even after allowance for alcohol, fruit and vegetables, supporting a real inverse association between this class of flavonoids and AMI risk.

Keywords:

Diet, Flavonoids, Myocardial infarction, Case–control studies, Risk factors

Flavonoids consist of over 4000 compounds present in food and beverages of plant origin, with antioxidant, anti-inflammatory, antithrombotic and endothelial protection activity^1,2. These properties have led to the hypothesis that they are protective against cardiovascular disease^2,3.

Several epidemiological studies have considered the relation of total flavonoids or specific flavonoids with ischaemic heart diseases, but the results are not clear^4–14. Data on specific classes of flavonoids using comprehensive databases and their effects on cardiovascular disease risk are few¹⁵. This is partly due to the lack, until recently, of a clear and complete classification and a reliable database on the flavonoid content of foods and beverages. A Greek case–control study carried out a systematic analysis of the effects of the six specific classes of flavonoids, and found an inverse association of flavan-3-ols with risk of coronary heart disease (CHD)¹⁶.

To further assess the relation of flavonoid classes with acute myocardial infarction (AMI) risk, we computed the dietary intake of the six principal classes of flavonoids (i.e. isoflavones, anthocyanidins, flavan-3-ols, flavanones, flavones and flavonols)^17,18 from dietary information collected in a case–control study of non-fatal AMI conducted in Italy.

Subjects and methods

Data derive from a case–control study of non-fatal AMI conducted in the greater Milan area, Italy, between 1995 and 2003¹⁹. Cases were 760 patients (580 men, 180 women; median age 61 years, range 19–79 years) with a first episode of non-fatal AMI, defined according to the World Health Organization criteria²⁰, admitted to a network of teaching and general hospitals in the area. Controls were 682 patients (439 men, 243 women; median age 59 years, range 16–79 years) from the same geographical area, admitted to the same hospitals for a wide spectrum of acute conditions not likely related to known AMI risk factors and diet. We excluded subjects with previous AMI or other major cardiovascular events. Among controls, 30% had traumas, 25% non-traumatic orthopaedic disorders, 18% acute surgical conditions, 18% eye, nose, throat or teeth disorders, and 9% miscellaneous other illnesses unrelated to diet. Less than 5% of the cases and controls approached refused to participate.

Interviews were conducted in hospital using a structured questionnaire, including information on sociodemographic factors, anthropometric variables, smoking, alcohol and coffee consumption, other lifestyle habits, physical activity, a problem-oriented medical history, and history of AMI in first-degree relatives. Cholesterol levels were obtained from clinical records.

Information on diet was based on a food-frequency questionnaire tested for reproducibility²¹ and validity²², which included questions on 78 foods or food groups and 15 questions aimed at assessing patterns of lipid intake and meal frequency. Energy and nutrient intakes were computed using an Italian food composition database²³. Food and beverage content of total and six classes of flavonoids (isoflavones, anthocyanidins, flavan-3-ols, flavanones, flavones and flavonols) was computed using data from the US Department of Agriculture's provisional flavonoid food composition database^17,18, further integrated with other sources^24–26. Major flavonoids included in these classes were: hesperidin and naringin for flavanones; epicatechin and catechin for flavan-3-ols; quercetin, myricetin and kaempferol for flavonols; apigenin and luteolin for flavones; cyanidin and malvidin for anthocyanidins; genistein and daidzein for isoflavones. In our population, oranges and other citrus fruits were the major sources of flavanones; tea, red wine, grapes and other fruits those of flavan-3-ols; various common vegetables and fruits were major sources of flavonols; vegetables, bean soups and tea those of flavones; red wine, red fruits onion and garlic were major sources of anthocyanidins; pulses those of isoflavones.

Data analysis

Odds ratios (OR) of AMI, and the corresponding 95% confidence intervals (CI), for subsequent quintiles of intake of various flavonoid classes were derived using unconditional multiple logistic regression models²⁷, including terms for sex, age, education, tobacco smoking, coffee, alcohol drinking, total energy intake, body mass index, physical activity, cholesterol levels, diabetes, history of hypertension and history of AMI in first-degree relatives. Flavonoids were also included in the models as continuous variables, with a measurement unit equal to one standard deviation of the distribution of all subjects.

Results

The distribution of cases of AMI and controls according to age, sex and other major covariates is shown in Table 1. Compared with controls, cases were more often smokers (OR=2.25 for current smokers of 15 or more cigarettes per day, P<0.0001) and heavy coffee drinkers (OR=1.42), consumed less alcohol (OR=0.72 for 2 or more drinks per day, P<0.01), more often had a history of hypertension (OR=1.58), diabetes (OR=2.92), and AMI in first-degree relatives (OR=2.17).

TBR1

Table 2 gives the distribution of cases and controls and the corresponding OR of AMI according to dietary intake of total flavonoids and of the six major classes of flavonoids. The mean daily intake in controls was 134.0 mg for total flavonoids, 25.5 μg for isoflavones, 19.2 mg for anthocyanidins, 55.6 mg for flavan-3-ols, 38.2 mg for flavanones, 0.44 mg for flavones and 20.6 mg for flavonols. After allowance for major confounding factors, including energy and alcohol intake, we found a reduced risk of AMI for increasing intake of anthocyanidins (OR=0.45 for the highest vs. the lowest quintile, P_trend=0.003) and possibly flavonols (OR=0.65, P_trend=0.02). A tendency toward reduced risks, although not significant, was observed for flavan-3-ols (OR=0.73) and total flavonoids (OR=0.74). Other flavonoids, including isoflavones, flavanones and flavones, were not associated with AMI risk. After further adjustment for intake of vegetables and fruit, the OR for the highest quintile of intake compared with the lowest one was 0.89 (95% CI 0.56–1.40) for total flavonoids, 1.23 (95% CI 0.82–1.85) for isoflavones, 0.55 (95% CI 0.33–0.91) for anthocyanidins, 0.84 (95% CI 0.57–1.25) for flavan-3-ols, 1.26 (95% CI 0.70–2.29) for flavanones, 1.42 (95% CI 0.95–2.11) for flavones and 0.90 (95% CI 0.57–1.41) for flavonols. The OR for a continuous term computed for an increment of intake corresponding to one standard deviation was 0.97 for total flavonoids, 0.82 for anthocyanidins and 0.87 for flavonols among all subjects. The corresponding OR were 1.02, 0.81 and 0.86 in men and 0.85, 0.72 and 0.86 in women; the estimates were not heterogeneous between the two sexes.

TBR2

Discussion

The present study adds epidemiological data on the relation between flavonoids and AMI. Reduced CHD mortality with higher intake of total flavonoids was found in the Zutphen Elderly Study cohort⁴, the Seven Countries Study cohort⁵, a Finnish cohort⁶ and the Iowa Womens’ cohort of postmenopausal women⁷, which also found protection with intake of kaempferol, a compound of the flavonol class. The ATBC (Alpha-Tocopherol Beta-Carotene) Cancer Prevention study reported no relation of consumption of flavonols and flavones combined with CHD mortality, but an inverse association with non-fatal AMI⁸. In contrast, the Male Health Professionals Study found no relation between non-fatal AMI and intake of flavonols and flavones combined, or with the individual flavonols quercetin, kaempferol and myricetin⁹. However, in the Rotterdam Study, the flavonols quercetin, kaempferol and myricetin were inversely related to risk of fatal AMI¹⁰. No relationship between flavonols and flavones with ischaemic heart disease mortality was found in the Caerphilly Study¹¹, whereas an inverse association was found in the Finnish Mobile Clinic Health Examination Survey with the flavonol quercetin¹². In the Women's Health Study, flavonoid intake was not associated with risk of cardiovascular disease¹³. A meta-analysis of seven prospective cohorts of men and women, including more than 2000 fatal CHD events, found an overall reduced risk with dietary flavonol intake (risk ratio of 0.80 for the highest tertile of intake compared with the lowest one)¹⁴.

The results of the present study indicate that intake of flavonoids is related to a reduced risk of non-fatal AMI, and that the strongest inverse association was observed for anthocyanidins. However, it is difficult to disentangle the effect of flavonoids from that of other dietary components, especially other antioxidants or other potentially cardioprotective components of vegetables, fruit and wine. In our study the inverse association of flavonoids with AMI risk was weaker after allowance for vegetables, fruit and alcohol (mainly wine in the Italian population), suggesting that the favourable effect of flavonoids on AMI risk found in this study may partly depend on other substances contained in these foods and beverages. However, these may well represent overadjustments, and the persistence of a protective effect of anthocyanidins also after adjustment for vegetables, fruit and alcohol supports a real inverse association between flavonoids and AMI risk. When alcohol was excluded from the multivariate model, a reduced risk was found for anthocyanidins (OR=0.44 for the highest quintile of intake compared with the lowest), flavan-3-ols (OR=0.67), flavonols (OR=0.64), total flavonoids (OR=0.58) and possibly for flavanones (OR=0.75), while no association was found with intake of isoflavones and flavones.

Soy proteins containing isoflavones have been reported to reduce circulating total and low-density lipoprotein (LDL) cholesterol and to increase high-density lipoprotein (HDL) cholesterol, but changes were related to level and duration of intake²⁸. The typical Western diet contains low quantities of soy products or soy derivatives in comparison with the Asian one²⁹. In the Italian diet, the intake of isoflavones is among the lowest of Western countries³⁰ and the levels at which soy isoflavones are reported to be protective are not consumed by the majority of population²⁸. Consequently our data are not very informative on this issue. The lack of association found for isoflavones is in agreement with the findings of the Dutch Prospect–EPIC cohort (European Prospective Investigation into Cancer and Nutrition)³¹, conducted in another Western population with low intake of isoflavones.

Flavonoids also have been shown to reduce oxidation of LDL³² and to increase cellular resistance to the deleterious effects of oxidised LDL³³. They also reduce the release of cardiac mast cell mediators and decrease inflammation, which has been implicated in CHD^34,35. Flavonoids also have favourable effects on endothelial function³⁶ and inhibit platelet aggregation³⁷.

In this study cases and controls were interviewed in the same hospitals, they came from the same geographical area, and their participation was similar and almost complete. We excluded from the comparison group patients admitted for chronic conditions or diseases related to known or potential risk factors for AMI, diet-related conditions and long-term modifications of diet. The food-frequency questionnaire was satisfactorily valid and reproducible^21,22, and there is no reason to assume different recall of intake of the major sources of flavonoids on the basis of disease status, since the possibility of a relationship between these compounds and AMI risk was unknown to the interviewers and probably to most subjects interviewed. A potential limitation of the study is the adaptability of the US flavonoid food composition database to the Italian diet. However, this is unlikely to have introduced spurious associations since the same food composition database was applied to the intakes of both cases and controls, and imprecise classification of exposure is likely to lead to an attenuation of any real association. Flavonoids may affect the risk of CHD, or death from CHD. Since the cases here were only AMI survivors, an inverse relation with mortality might have attenuated any real association. Furthermore, we cannot exclude that healthier lifestyle may play a role in the inverse association of flavonoid intake with AMI risk. However, the potential confounding of covariates associated to AMI risk in this study^38,39 was allowed for in the analysis.

Acknowledgements

The work was conducted with the contribution of the Italian Association for Cancer Research and the Italian League Against Cancer. The authors thank Drs A Lualdi (Istituto di Cardiologia, Università degli Studi di Milano, Centro Cardiologico Monzino, IRCCS, Milan, Italy), A Mafrici (Cardiology Department, Niguarda Ca’ Granda Hospital, Milan, Italy) and O Parodi (CNR Clinical Physiology Institute, Milan, Italy) for their helpful contribution to the clinical conduct of the study.

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^CA1Corresponding author: Email: tavani@marionegri.it 

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