Some scientists have proposed mild cognitive impairment as a transitional stage before the development of Alzheimer’s disease, one of the most common causes of dementia. Epidemiological evidence suggests that vitamin supplementation may support cognitive function. New research demonstrates reduced oxidative stress and improved cognition after 12 months of vitamin D supplementation.

Current evidence suggests that lifestyle factors like diet influence the progression of cognitive decline by increasing or decreasing oxidative stress that damages the brain. Previous studies have demonstrated the association between telomere length, a marker of DNA integrity, and mild cognitive impairment or Alzheimer’s disease progression. Vitamin D supplementation has been shown to improve working memory; however, the mechanisms that drive these improvements are unknown.

The randomized placebo-controlled study involved 183 participants who had mild cognitive impairment. Approximately half of the participants took 800 international units of vitamin D daily for one year, and the remainder took a placebo. The authors of the study assessed the participants' cognitive function and measured key biomarkers, including telomere length and markers of oxidative stress.

Participants who took vitamin D performed significantly better on tests of cognitive function. Supplementation also increased telomere length and decreased markers of oxidative stress in the blood.

The authors believe their findings are consistent with previous studies demonstrating the protective effects of vitamin D in the brain. The optimal dose of vitamin D is unknown and likely varies between individuals, limiting the ability to interpret these results. The authors also noted that blood markers of oxidative stress may not be a reliable measure of the brain environment. Future research should include more participants and a longer length of supplementation.

• Link to full study.