By Jonathan Cerna, BS Dietetics, MS Student in Nutritional Sciences and Dietetic Intern
Advice on how to feed a healthy brain does not need to deviate from Michael Pollan’s simple but powerful advice, “Eat food, not too much, mostly plants”. Effectively, this pointer extends to brain health because mounting evidence shows that certain carotenoids, plant pigments mostly found in fruits and vegetables, might be neuroprotective.
Multiple lines of evidence show that lower serum carotenoid concentrations are detrimental for maintenance of critical functions supported by the central nervous system, such as walking speed, visual acuity and contrast sensitivity. Among carotenoids, the xanthophyll partners lutein and zeaxanthin, should be held in special regard. Not only do they harness antioxidant and immunomodulating properties, but lutein and zeaxanthin also preferentially accumulate in the brain, despite being amongst the lowest circulating carotenoids. This points to their potential importance for brain function.
Lutein and zeaxanthin cannot be made by our bodies and must be consumed through diet or supplementation. In support of their potential neuroprotective role, supplementation has shown to increase cognitive performance in healthy, and older adults, as well as preserve brain morphology in aging adults. However, the link between cognitive performance and carotenoids consumed via diet had never been confirmed in large cohorts… until now. A study recently published in the journal of Nutritional Neuroscience using data from the National Health and Nutrition Examination Survey (NHANES) 2011-2014, looked at the consumption of lutein and zeaxanthin in 2796 participants aged > 60. Effectively, they reported results similar to previous findings. Higher consumption of lutein and zeaxanthin was associated with higher cognitive measures of memory, language, and executive function domains (i.e., higher order functions such as planning, thinking, self-control, etc).
The question is: what mechanisms are at play here? The simplest explanation might be that higher intake of these xanthophylls is simply an indicator of an overall healthier diet. Foods highest in lutein and zeaxanthin include kale, spinach, swiss chard, and mustard greens. Similarly, a diet pattern higher in vegetables is characteristic of the Mediterranean diet, which has shown to have positive effects on cognitive aging, and neurological diseases such as Alzheimer’s Disease. Another proposed mechanism is that of increased neural efficiency, which had not been corroborated with functional neuroimaging work until recently. Results from this work conducted using functional magnetic resonance imaging (fMRI) showed that these carotenoids improve visual processing in primary visual areas in the brain, lending credence to the claim that they are improving function beyond the retina.
Understanding exactly how these xanthophylls help to preserve structural integrity and function proves to be a difficult task, but there are a few ideas of what might be going on. One reason why their accumulation might be so beneficial is that their molecular structure allows for localization around areas that are prone to oxidation. Oxidative stress is caused by higher levels of damaging molecules called reacting oxygen species (ROS), inducing cellular damage. Therefore, areas such as the brain, rich in polyunsaturated fatty acids (PUFAs) such as docosahexaenoic acid (DHA), are notoriously prone to oxidation. Interestingly, in rhesus monkeys (one of the few animal models with similar brain xanthophyll accumulation as us), lutein has been shown to accumulate in subcellular membranes of key brain regions and protect against DHA oxidation. Similarly, lutein has been shown to accumulate around myelin, fatty sheaths which help electrical impulses in our brain propagate appropriately.
All of this evidence points to the critical importance of eating your fruits and veggies. However, it is worth noting that separating the cognitive effects of these carotenoids from other beneficial nutrients is not often done. Given that xanthophyll consumption might be a surrogate marker of a healthy diet, future work needs to separate the effects of these xanthophylls above and beyond a healthy diet. Lastly, no studies have been able to examine concentrations of lutein and zeaxanthin in the brain while looking at brain function, they have only been able to examine their associations with macular xanthophyll accumulation (a more chronic marker of xanthophyll accumulation) and serum xanthophyll circulation (acute marker easily affected by daily consumption). Nevertheless, these limitations do not negate the importance of following the simple advice introduced at the beginning to protect and improve your brain health: “Eat food, not too much, mostly plants”.
Peer-Edited by Michaela Copp, BE Chemical Engineering, PhD Student in Biomedical Engineering
Image credit: The Spark