A U.K. study that measured diet and cognitive decline over an almost 25-year period did not show an association between a healthier diet in midlife and a lower risk for dementia later in life. The findings, published March 12 in JAMA, are the first to examine the prospective association of diet quality in midlife with later life risk of developing dementia with a follow-up of greater than 10 years.
Previous observational studies with shorter follow-up periods have shown a relationship between diet and cognitive decline, brain volume, and dementia risk, but intervention studies have not shown an effect. In this NIA-supported analysis, researchers rated the self-reported diets of 8,225 participants (mean age 50 years in 1991-1993) in Whitehall II, also known as the Stress and Health Study. Participants filled out dietary questionnaires at three different time periods. Researchers used the Alternative Healthy Eating Index (AHEI)—an 11-component diet quality score—to score and index the quality of participants’ midlife diets.
Over a 24.8 median follow-up period, 344 participants (average age, 75.6) were diagnosed with dementia, as identified through electronic health records from the U.K. National Health Service. When researchers compared dementia incidence rates with diet quality, they found no significant associations. Researchers also found no associations between diet and cognitive decline.
During analysis researchers controlled for several factors, including sociodemographic, behavioral risk factors, and certain health conditions. The diet quality metric used in this study did not show any effect over and above other risk factors, such as high blood pressure and diabetes, that themselves may be in part attributable to diet.
These findings do not contradict the possibility that a diet specifically designed to promote brain health (like some versions of the Mediterranean diet) would have any beneficial effect. It does suggest that some positive effects of better diets on cognition might be due to their direct effect on known risk factors that are not brain-specific like high blood sugar or high blood pressure.
This research was funded in part by NIA grants R01AG056477 and R01AG034454.
Reference: Akbaraly TN, et al. Association of midlife diet with subsequent risk for dementia. JAMA. 2019 March 12. 321(10):957-968. doi:10.1001/jama.2019.1432