Investigators found that individuals with the highest serum levels of lutein + zeaxanthin and beta-cryptoxanthin at baseline were less likely to have dementia decades later than were their peers with lower levels of these antioxidants.
Lutein and zeaxanthin are found in green leafy vegetables such as kale, spinach, broccoli, and peas. Beta-cryptoxanthin is found in fruits such as oranges, papaya, tangerines, and persimmons.
“Antioxidants may help protect the brain from oxidative stress, which can cause cell damage,” first author May A. Beydoun, PhD, with the National Institute on Aging (NIA), said in a news release.
“This is the first nationally representative study to analyze blood levels of antioxidants in relation to dementia risk,” NIA scientific director Luigi Ferrucci, MD, said in an interview.
“Blood test results may be more representative of the actual antioxidant level than a person’s report of what kind of foods they regularly consume,” Dr. Ferrucci added.
The study was published online in Neurology.
Reduced dementia risk
The researchers tested associations and interactions of serum vitamins A, C and E, and total and individual serum carotenoids and interactions with incident Alzheimer’s disease (AD) and all-cause dementia.
They analyzed data from 7,283 participants in the Third National Health and Nutrition Examination Survey (NHANES III) who were at least 45 years old at baseline and followed for an average of 16-17 years.
They found serum levels of lutein + zeaxanthin were associated with reduced risk of all-cause dementia among people aged 65 and older in models adjusted for lifestyle.
For lutein + zeaxanthin, every standard deviation (SD) increase (roughly 15.4 µmol/liter) was associated with a 7% decrease in risk for dementia (hazard ratio [HR] 0.93; 95% confidence interval [CI], 0.87-0.99, P = .037). This association was attenuated somewhat after adjustment for socioeconomic status.
Serum levels of beta-cryptoxanthin showed a “strong” inverse relationship with all-cause dementia in age- and sex-adjusted models.
For beta-cryptoxanthin, every SD increase (roughly 8.6 µmol/liter) was associated with a 14% reduced risk for dementia in people aged 45 and older (HR, 0.86; 95% CI, 0.80-0.93, P < .001) and 65 and older (HR, 0.86; 95% CI, 0.80-0.93, P = .001).
This relationship remained strong in models adjusted for sociodemographic and socioeconomic factors but attenuated in subsequent models.
No associations were found for lycopene, alpha-carotene, beta-carotene, or vitamins A, C, or E in the fully adjusted models.
Antagonistic interactions were observed for vitamin A and alpha-carotene, vitamin A and beta-carotene, vitamin E and lycopene, and lycopene and beta-carotene, suggesting putative protective effects of one antioxidant at lower levels of the other, the researchers noted.
“This analysis of an observational study found that the most important carotenoids in potentially protecting the brain may be lutein + zeaxanthin and beta-cryptoxanthin. However, randomized controlled trials are needed to prove causality,” said Dr. Ferrucci.
“Experts do not yet know the daily level of antioxidant intake to promote healthy aging of the brain. More research is needed to establish the necessary level of antioxidant intake – through the diet and/or supplements – to promote brain health and healthy aging,” he added.