What are carotenoids, and can they protect against dementia?

Carotenoids are pigments produced by many vegetables (carrot, sweet potato, spinach, kale, pepper, pumpkin, etc.) and fruits (mango, orange, apricot, kiwi, grapes, etc.), often producing bright orange, yellow, or red colors. Carotenoids act as antioxidants and are often associated with eye health, cancer prevention, and immune system function [1]. But can carotenoids also be beneficial for brain health? A recent observational study reported that people who have higher levels of carotenoids in their blood were less likely to develop dementia [2].

These findings come from the National Health and Nutrition Examination Survey, which enrolled over 7,000 participants (age 45-90 years old at the start of the study) representing all of the US [2]. Participants had their blood drawn and were thoroughly interviewed on their diet, health, lifestyle, and demographic information. Researchers followed these participants for up to 26 years to see who developed dementia. The study found that higher blood levels of lutein and zeaxanthin, two carotenoids best known for protecting eye health, were associated with lower risk of dementia. Lutein and zeaxanthin are found in dark leafy greens, orange pepper, zucchini, squash, and other vegetables. Researchers also found an association between higher blood levels of another carotenoid, β-cryptoxanthin, and lower risk of dementia. β-cryptoxanthin is rich in papaya, orange, peach, tangerine, and others.

It may be tempting to think that taking supplements of these carotenoids may be an easy way to protect against dementia. However, it is important to note that this study was an observational study, which means the study was designed to find associations, but it was not designed to prove cause and effect like a randomized controlled trial. The study showed that while higher blood levels of carotenoids were associated with a reduced risk of dementia, after controlling for lifestyle, health, and diet-related factors, the relationships became weaker. The weakened relationships suggest that people who have high blood levels of carotenoids may practice other healthy habits in addition to eating a diet rich in carotenoids, and it is probably not just a few carotenoids that are driving the lower risk of dementia. Thus, an overall healthy lifestyle that includes a healthy diet rich in vegetables and fruits is likely necessary to maintain optimal brain health.

The findings from this study are consistent with the growing body of literature suggesting that a diet rich in fruits, vegetables, fish, whole grains, legumes, and nuts is beneficial for brain health [3; 4; 5; 6]. The results are also in line with our recommended Seven Steps to Protect your Cognitive Vitality: eat a brain-healthy diet, get 7-8 hours of sleep per night, get plenty of physical exercise, alleviate stress, be social, keep learning new things, and manage chronic illnesses such as high blood pressure and diabetes.

1. Milani A, Basirnejad M, Shahbazi S et al. (2017) Carotenoids: biochemistry, pharmacology and treatment. British journal of pharmacology  174, 1290-1324.
2. Beydoun MA, Beydoun HA, Fanelli-Kuczmarski MT et al. (2022) Association of Serum Antioxidant Vitamins and Carotenoids With Incident Alzheimer Disease and All-Cause Dementia Among US Adults. Neurology.
3. Ballarini T, Melo van Lent D, Brunner J et al. (2021) Mediterranean Diet, Alzheimer Disease Biomarkers and Brain Atrophy in Old Age. Neurology.
4. Croll PH, Voortman T, Ikram MA et al. (2018) Better diet quality relates to larger brain tissue volumes: The Rotterdam Study. Neurology  90, e2166-e2173.
5. Dhana K, Evans DA, Rajan KB et al. (2020) Healthy lifestyle and the risk of Alzheimer dementia: Findings from 2 longitudinal studies. Neurology  95, e374-e383.
6. Holland TM, Agarwal P, Wang Y et al. (2020) Dietary flavonols and risk of Alzheimer dementia. Neurology  94, e1749-e1756.

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