A long-term diet rich in vegetables, fruit, and orange juice was tied to lower risk of memory loss in men, a prospective study found.

Greater intake of total vegetables, total fruit, and fruit juice across middle to late adulthood were associated with lower odds of moderate poor subjective cognitive function in later life, reported Changzheng Yuan, ScD, of the Harvard T.H. Chan School of Public Health in Boston, and colleagues.

Leafy greens, dark orange and red vegetables, and berry fruits showed the strongest links in subgroup analyses. And a vegetable- and fruit-rich diet 18-22 years earlier was linked with lower odds of poor cognitive function independent of more recent eating patterns, they wrote in Neurology.

"One of the most important factors in this study is that we were able to research and track such a large group of men over a 20-year period of time, allowing for very telling results," Yuan said in a statement. "Our studies provide further evidence dietary choices can be important to maintain your brain health."

The study looked at repeated assessments of diet over 20 years in the Health Professionals Follow-up Study, a prospective cohort of American men who were dentists, optometrists, pharmacists, podiatrists, and veterinarians. The analysis included 27,842 men with a mean age of 51 years at enrollment in 1986.

Every 4 years, participants completed a validated semi-quantitative food frequency questionnaire about their usual intake of foods and beverages over the preceding year, with frequencies ranging from <1 serving/mo to 6 or more times/day. Participants also self-reported subjective cognitive function, answering six questions about changes in memory and cognition on paper questionnaires mailed to them in 2008 and 2012.

At the time of cognitive assessment, men were an average of 73 years old; 54.7% had good subjective cognitive function, 38% had moderate function, and 7.3% had poor function. After controlling for major non-dietary factors and total energy intake, higher consumption of total vegetables, total fruits, and fruit juice each were significantly associated with lower odds of moderate or poor subjective cognitive function. Adjusting further for major dietary factors weakened the link with fruit intake.

For vegetable intake, the top versus bottom quintile had a multivariate OR of 0.83 (95% CI 0.76–0.92, P<0.001 for trend) for moderate subjective cognitive function, which dropped to OR 0.66 (95% CI 0.55–0.80, P<0.001 for trend) for poor cognitive function.

For orange juice, compared to <1 serving/mo of intake, daily consumption was associated with a substantially lower odds of poor subjective cognitive function (OR 0.53, 95% CI 0.43–0.67; P<0.001 for trend).

Links between vegetable, fruit, and fruit juice intake and cognitive function were similar across age, disease status, and APOE e4 allele carrier status. After incorporating marital status, working status, living arrangement, happiness, life satisfaction, and optimism into the model, results were unchanged.

In vegetable and fruit subgroups analyses, higher consumption of green leafy vegetables, carotenoid-rich vegetables, and berry fruits were significantly associated with reduced odds of both moderate and poor cognitive function.

"This is a powerful study which provides both novel and supportive insight into how nutrition may influence cognitive decline in aging adults," said Keenan Walker, PhD, of the Johns Hopkins University School of Medicine, who was not involved in the study. "What is particularly relevant, from both a clinical and a neurobiological perspective, are the associations that emerged between consumption of vegetable and fruit from specific subgroups and later subjective cognitive function."

"Future research will be needed to understand which dietary components in particular are beneficial to brain health, and which biological pathways these nutrients may act on to exert a neuroprotective effect," Walker told MedPage Today. "Relating the intake of fruits and vegetables to neuroimaging markers of structural and functional brain health would also be helpful in further supporting the findings presented in this study."

This study had several limitations, Yuan and co-authors noted. Cognitive function was self-reported and was not tested at baseline; the authors assumed that, since all participants completed professional training, they had relatively high cognitive function in early adult life. Participants who did not complete the 2012 follow-up questionnaire may have been more likely to have cognitive difficulty. The study shows associations only, not causation, and unknown confounders may have influenced results. And the homogeneous population of male health professionals limits whether these findings could apply to other groups, including women.