The lead author, Christine C. Tangney, an associate professor of nutrition at Rush Medical College in Chicago, said sticking to the diet made a large difference. Those in the top third for adherence, she said in a telephone interview, were cognitively the equivalent of two years younger than those in the bottom third.
The study, published in The American Journal of Clinical Nutrition, has significant strengths in its prospective design, large sample and use of a well-validated dietary questionnaire. But the authors acknowledged that they could not account for all possible variables, and cautioned that it was an observational study that draws no conclusions about cause and effect.