a1 Department of Nutrition and Public Health Intervention Research, Faculty of Epidemiology and Population Health, London School of Hygiene & Tropical Medicine, Keppel Street, London WC1E 7HT, UK
a2 Nutritional Epidemiology Research Unit, University of Paris XIII, Bobigny, France
a3 Department of Public Health Nutrition, Institute of Nutrition and Food Technology (INTA), University of Chile, Santiago, Chile
Oily fish and other sources of long-chain n-3 polyunsaturated fatty acids (n-3 LCPs) have been proposed as protective against dementia and age related cognitive impairment. The basic mechanisms underlying these proposed benefits have been postulated and experimental studies supporting the plausibility of the putative effects have been published. Observational epidemiological and case control studies also largely support a protective role of fish consumption on cognitive function with advancing age, albeit with important unexplained heterogeneity in findings. In this review we report the findings of the latest Cochrane review on the benefits of n-3 LCP supplementation on cognitive function among cognitively healthy older people and expand the review by including trials conducted with individuals with prevalent poor cognitive function or dementia. We identified seven relevant trials, four among cognitively healthy older people, and three among individuals with pre-existing cognitive decline or dementia, and overall conclude that there is no evidence to support the routine use of n-3 LCPs supplements for the prevention, or amelioration, of cognitive decline in later life. We identified several challenges in the design of intervention studies for the prevention of dementia and cognitive decline in older people that require careful consideration especially in recruitment and retention in long-term trials. Whether the lack of agreement in findings from mechanistic and observational data and from intervention studies reflects a real absence of benefit on cognitive function from n-3 LCP supplementation, or whether it reflects intrinsic limitations in the design of published studies remains open to question.
Abbreviations: AD, Alzheimer's disease; ALA, alpha-linolenic acid; BIS, Barratt Impulsiveness scale; CVLT, California Verbal Learning Test; DHA, docosahexaenoic acid; EPA, eicosapentaenoic acid; MMSE, Mini-Mental State Examination; n-3 LCPs, n-3 long-chain polyunsaturated fatty acids