Differential relations between cognition and 15N isotopic content of hair in elderly people with dementia and controls

Abstract

Background. Previous researchers have suggested that a vegetarian diet or one rich in fish may protect against Alzheimer's disease (AD). However, assessing diet is difficult in AD patients. 15N:14N isotopic ratios (δ15N) of body proteins can estimate long-term dietary habits in a way that does not depend on memory. δ15N is high in people who eat a lot of fish and low in vegetarians. Methods. To choose between the vegetarian and fish hypotheses of AD, we compared dietary questionnaire reports and δ15N of hair samples from AD patients and controls. Results. Patients' cognitive scores related directly to reported frequency of eating fish and to hair δ15NAIR but inversely to reported frequency of eating beans. Homocysteine levels related inversely to hair δ15NAIR in controls, but not in patients. Dietary questionnaire reports accounted for slightly more variance in δ15NAIR in patients than controls. Therefore, our questionnaire assessed dietary habits as reliably for individuals with AD as for cognitively unimpaired controls. Conclusions. A diet rich in fish may ameliorate AD, possibly by lowering homocysteine, but more vegetarian diets do not. In fact, eating beans correlated with worse cognition in AD patients. Further studies should test if restricting the intake of beans slows the progression of AD.