Previous studies have demonstrated that levels of certain blood metabolites are associated with cognitive function and dementia. Levels of blood metabolites can be influenced by genetics, environmental factors, lifestyle factors, socioeconomic factors, as well as health status, and they can also differ among different ethnic or racial groups. Characterizing metabolites can help researchers understand the mechanisms underlying disease development, and they can be measured easily to serve as biomarkers.
This study characterized blood metabolites associated with cognitive function among various racial/ethnic groups. Findings suggest that dietary habits could potentially influence levels of these metabolites and cognitive performance drawing more attention to the importance of maintaining a healthy diet.
Dr. Tamar Sofer, a professor at Brigham and Women’s Hospital at Harvard University said,” We identified a few metabolites (small molecules) in the blood that their levels are correlated with cognitive function, and they are all related to diet. While there are clinical trials showing that diet can influence cognitive function, identifying specific metabolites can help identify [a] specific mechanism, specific components of [a] diet that are more important than others, and biomarkers to measure [the] success of dietary changes.” Adding that “There is still work to do to make these steps happen, but this is a good start, especially because the results held up in a few different studies, so the findings are very reliable.”
Another study showed that levels of 13 blood metabolites were associated with global cognitive function. Given that metabolite levels are influenced by a multitude of factors, the authors examined whether the results from the BPRHS study could be replicated in different samples of Puerto Rican heritage within America, and they also investigated if the findings could be generalized to the broader Hispanic/Latino population as well as other ethnic groups.
The BPRHS study identified several metabolites that can be influenced by dietary habits, indicating that making healthful modifications to dietary habits could be a possible intervention to help preserve cognitive health, the researcher also examined the causal role of the blood metabolites and dietary habits influencing cognitive function.
To assess the generalizability of the BPRHS findings the researchers used data from 2,222 adults enrolled in the HCHS/SOL Study, and using blood samples from this study the researchers estimated the levels of 11 of the 13 metabolites assessed in the BPRHS. The direction of the effects of blood metabolites on cognitive function in the HCHS/SOL Study and all participants were found to be similar to those observed in the BPRHS.
A significant correlation was found between levels of certain metabolites with global cognitive function in all HCHS/Sol participants. Higher levels of beta-cryptoxanthin and lower levels of gamma-CEHC glucuronide were associated with cognitive function.
To examine the association between blood metabolites and cognitive function in other racial/ethnic groups data from 1,365 European Americans and 478 African Americans enrolled in the ARIC Study.
A meta-analysis was then conducted to assess the associations between blood metabolite levels and cognitive levels using data from the ARIC, BPRHS, and HCHC/SOL studies. Results showed that 6 blood metabolites were associated with lower cognitive function across all groups: and 4/6 of the metabolites associated with overall cognitive function were sugars, including glucose, ribitol, mannose, and mannitol/sorbitol. The previous analysis only found a correlation between cognitive function and metabolites, additional analysis only revealed a potential causal effect for ribitol on cognitive function.
The association between dietary habits on blood metabolite levels was also assessed. Results showed that adhering to a Mediterranean-style diet or its component food group was correlated with several blood metabolites, with the strongest association being observed between beta-cryptoxanthin and fruit intake. Beta-cryptoxanthin is a carotenoid with antioxidant properties found in fruits and vegetables.
Food groups did play causal roles in cognitive performance, but cognitive function(associated with socioeconomic status that may mediate effects of cognitive status on dietary habits) had a much stronger causal effect on the intake of specific food groups. In all, results indicate that dietary habits could influence cognitive performance by modulating metabolite levels.
This study was not without limitations such as the previous studies using different methods for assessing cognitive function, and the causal effects must be interpreted with caution.
“There are several challenges in interpreting these results in relation to the role of specific nutritional groups and brain health. This is a cross-sectional study from which causal relationships cannot be drawn. Not only can nutrition affect brain health, but poor cognitive function can also influence nutrition, suggesting a bi-directional relationship,” said Dr. Perminder Sachdev, who is a professor of neuropsychiatry at the University of New South Wales. Sachdev also pointed out that, “blood metabolites have multiple determinants, with diet being only one of them. Genetic factors, health co-morbidities, and lifestyle are all important. A direct attribution to diet is therefore difficult.”
Adding that much more work is required Sachdev said that “We need to understand the plasma metabolome better to know what determines their blood levels before we can begin to interpret such studies. We need longitudinal studies with multiple measurements in large samples, followed by intervention studies, so that causal relationship can be established.” Adding that “This study is a step in the right direction in relation to examining the role of diet and the body’s metabolism for brain health. It provides suggestive evidence that adherence to a good diet such as the Mediterranean style diet may be beneficial for brain health over a wide age range.”
