Abstract
The potential role of dietary poly-unsaturated fatty acids (PUFA) in the prevention of dementia and Alzheimer’s disease arouses increasing interest. Fatty fish is very rich in long-chain n-3 PUFA, in particular in DHA which is also a major component of neuron membranes. The Rotterdam Study, the French PAQUID and Three-City studies, and the Chicago Health and Aging Project found a protective effect of fish or long-chain n-3 PUFA consumption against dementia or cognitive decline. In the Three-City Study we showed that regular use of omega3 rich oils was also associated with a decreased risk of borderline significance for all cause dementia. Biological data are congruent with the results obtained with dietary data. No intervention study evaluating the effect of n-3 PUFA in the primary prevention of dementia in human has been published. Despite the negative results of the OmegAD intervention trial in patients with moderate AD, these results considered all together suggest a protective effect of long-chain n-3 PUFA against cognitive decline and dementia. However, the complex mechanisms of action of PUFA at the different stages of brain aging and their interaction with the apolipoprotein E genotype still have to be elucidated.
Highlights
As a consequence of population aging, the prevalence of dementia is increasing all around the world [1]
The epidemiological cohorts analysing the relationships between nutrition and brain aging must record dietary and biological data in large samples representative of the elderly population, with a follow-up long enough to ensure the anteriority of dietary behaviour relatively to cognitive decline assessed by repeated neuropsychological testing and an active search for incident cases of dementia
The Washington Heights Inwood Columbia Aging Project (WHICAP) study found no association between polyunsaturated fatty acids (PUFA) intake and risk of Alzheimer’s disease (AD), but this study showed a deleterious effect of total energy intake and total fat intake in participants with the apoE4 allele [26]
Summary
Prospective longitudinal studies (i.e. cohort studies) are relevant in a disease whose main symptom is memory decline. The epidemiological cohorts analysing the relationships between nutrition and brain aging must record dietary and biological data in large samples representative of the elderly population, with a follow-up long enough to ensure the anteriority of dietary behaviour relatively to cognitive decline assessed by repeated neuropsychological testing and an active search for incident cases of dementia. Few longitudinal epidemiological studies have examined the relationships between dietary fat and risk of dementia or cognitive decline but most of their results converge to show a protective effect of n-3 PUFA despite the great variability in dietary habits (table 1). The protective effect of fish consumption on risk of dementia was first found in the Rotterdam Study [18], but with a mean follow-up of only 2.1 years, the participants might have modified their dietary behaviour because of incipient cognitive impairment.
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