Healthy Diet in Midlife May Not Stave Off Dementia

A high-quality diet in midlife did not seem to be protective against dementia, long-term data suggested.

During a median follow-up of nearly 25 years, a better quality diet in midlife as measured by the Alternative Healthy Eating Index (AHEI) was not significantly associated with a subsequent risk for dementia, reported Tasnime Akbaraly, PhD, of University Research and Hospital Center of Montpellier in France, and colleagues in JAMA.

Looking at dietary exposures of this group of middle-age adults (mean age 50.2) throughout three time periods of life, a better diet — each 1-SD increment higher on the 10-point scale — was not tied to a lower risk for dementia risk when compared with the worst diet:

• Dietary exposures 1991-1993: adjusted HR 0.97 (95% CI 0.87-1.08)
• Dietary exposures 1997-1999: aHR 0.97 (95% CI 0.83-1.12)
• Dietary exposures 2002-2004: aHR 0.87 (95% CI 0.75-1.00)

“Slower cognitive decline and reduced risk for dementia have been found with adherence to the recommended food score, the Dietary Approaches to Stop Hypertension (DASH), the Mediterranean-DASH Intervention for Neurodegenerative Delay diet, and the AHEI in some but not all studies,” the authors stated. “The Mediterranean diet is by far the index that received the most attention, and it has been shown to be associated with better cognitive outcomes in some but not all studies.”

However, Akbaraly’s group explained that prior studies that had a follow-up period <10 years might not have accurately measured the association between diet and cognitive dysfunction, leading to inconsistencies in the literature.

For this analysis, the researchers drew upon 8,225 middle-age participants of the Whitehall II study, which included middle-age adults residing in London. Diet quality was measured with a comprehensive 127-item food frequency questionnaire, which was used to rank the individual’s AHEI diet score.

However, the researchers noted the limitation of using a food frequency questionnaire for its wide margin of error in participants’ self-reporting data. A higher intake of vegetables, fruits, whole grains, nuts and legumes, long-chain omega-3 fatty acids, and polyunsaturated fatty acids placed the person in a higher tertile of diet quality, while more consumption of sugar-sweetened drinks and fruit juice, red and processed meat, trans fat, and sodium lowered diet score. Moderate consumption of alcohol was considered to be ideal in this diet score.

Based on diet score, the adults were divided into three tertiles of diet quality: worst, intermediate, and best. At baseline, rates of physical activity, type 2 diabetes, and dyslipidemia didn’t vary greatly between the diet quality groups, although the “best” dieters did report a higher amount of moderate alcohol consumption (72.8% of best diet vs 51.2% of worst diet).

Electronic health records were used to ascertain a diagnosis of incident dementia up until 2017. Throughout the nearly 25-year follow-up period, 344 incident cases of dementia were identified among this group, with an average age of 76 at the time of diagnosis.

Despite the lack of significant association between diet quality and dementia, Akbaraly’s group pointed out how their findings “suggested a slight decrease in diet quality in the years preceding dementia diagnosis, which also was reported in another study, and is compatible with the hypothesis that change in diet quality is a feature (among others) of preclinical dementia,” which could be the basis for future research in this area.

last updated 03.12.2019