N° 44 | April 2010

Dietary habits and cognitive decline in a cohort of elderly French women

Diet, a promising avenue of investigation to prevent ageing

Cognitive decline is a major cause of autonomy loss in the elderly, and represents an important public health challenge. Emerging evidence suggests that a “prudent diet”, characterized by high intakes of fruits and vegetables, unsaturated fatty acids and whole grains may contribute to slow down cognitive ageing. However, data on the long-term relationship remains limited and even conflicting.

To determine the potential impact of dietary habits on cognitive ageing, we analysed data from 4,809 elderly women (born between 1925 and 1930) participating in the “Etude Epidémiologique de Femmes de la Mutuelle Générale de l’Education Nationale” (E3N), a French prospective cohort. In 1993, cohort participants received an extensive diet history selfadministered questionnaire covering daily consumption of 208 foods and beverages. In the present study, diet was evaluated through the usual intakes of 25 food-groups and 33 nutrients. In 2006, another questionnaire on recently-observed cognitive change and Instrumental Activities of Daily Living (IADL) was sent to a close relative of each elderly woman. Logistic models adjusted for various lifestyle and medical factors were performed to evaluate associations between habitual dietary intakes and two aspects of cognitive functioning, based on informant report: cognitive decline over a period of one year and cognitive status as reflected in current impact in IADL functioning.

How was diet associated with aging outcomes?

In 2006, elderly women participating in the E3N cohort that were reported by informants to undergo recent cognitive decline had, 13 years previously, lower intake of poultry, fish, and animal fats, as well as higher intake of dairy desserts and ice-cream. They had lower than usual intake of dietary fibre and n-3 fatty acids, but higher intake of retinol.

Furthermore, elderly women that were reported by informants to have IADL impairment, had in the past, lower intake of vegetables, vitamins B2, B6, and B12. Our findings of significant associations between age-related decline and lower long-term intake of certain specific nutrients - namely n-3 fatty acids, dietary fibre, and vitamin B6 - has already been described, but generally in studies with shorter prospective design. One of the main interests of our study lies indeed in the more-than-a-decade time interval between dietary and cognitive/functional assessment, which has enabled us to explore the long-term effect of dietary habits in ageing. Our study is not in complete agreement with previous ones in showing that higher intake of retinol and lower intake of animal fats were both associated with cognitive decline. Potential explanations include residual confounding and chance resulting from multiple analyses. Also, where several epidemiologic studies found an association between cognitive decline and lower intake of fruits, vitamin C, vitamin E or β-carotene intake (in agreement with the antioxidant hypothesis), we only observed a borderline association with vitamin C. The limited range of intake in our highly educated population, with few women having low consumption levels in foods rich in antioxidant components may explain the absence of certain associations in our study.

What next?

Anti-inflammatory and antioxidant properties are suggested to account for the inverse association between age-related decline and dietary fibre and vegetables. N-3 fatty acids, in which fish is rich, could act on heart and brain not only through the vascular pathway but also through different cellular mechanisms: heart rhythm, neurotransmission, neuroprotection, neurogenesis.

Similarly, some B vitamins and homocystein can act directly on brain cell functioning. Although underlying biological pathways are not yet fully elucidated, our study, together with previous studies, supports that prevention of cognitive decline may be reached through a balanced diet rich in vegetables, fish and poultry, and limited in sweet dairy products, not only in later life but starting in middle age. These recommendations, also suggested for cancer and cardiovascular protection, may well work to enhance the quality of life as a whole.