October 21, 2026
Older adults with mild cognitive impairment and sleep problems may benefit from supplements containing relatively high doses of vitamin D, a small study found. The findings add to growing evidence that maintaining adequate levels of vitamin D may be important for brain health.
The study, from researchers at Emory University, looked at 54 men and women who had been diagnosed with mild cognitive impairment, a serious memory disorder that may progress to full-blown Alzheimer’s disease. Their mean age was 67. All also suffered from insomnia and other sleep disturbances, a common problem in those with cognitive impairment.
The researchers found that study participants who reported taking 5,000 IU or more of vitamin D daily scored 13 percent higher on a widely used test of thinking and memory skills called the Montreal Cognitive Assessment than those who did not take vitamin D or who took lower doses of the vitamin. The researchers considered various factors that may affect cognition, such as age and education levels, and found that higher doses of vitamin D seemed to be independently associated with higher cognitive scores.
It also didn’t matter which form of vitamin D that participants took. Some took D2, which comes from plant sources, and others took D3, from animal-based foods. Both forms of vitamin D seemed to provide similar benefits for cognitive health.
“In older adults experiencing both sleep disturbance and mild cognitive impairment, this may represent a critical window for intervention, when cognitive changes are emerging but opportunities to support brain health may remain,” said Victoria Pak, the study’s senior author and an associate professor at Emory’s School of Nursing. “Identifying accessible and modifiable factors, such as vitamin D supplement intake, during the earlier stages of cognitive decline may become increasingly important.” The findings were published in the journal Sleep Medicine.
The study was small, so further research is needed to confirm the findings. It was also observational so cannot prove cause and effect. But a growing body of research suggests that vitamin D is critical for brain health.
A study from earlier this year, for example, found that men and women with low vitamin D levels in their 30s and 40s were at increased risk of having brain changes typical of Alzheimer’s disease later in life. Other studies have found that memory skills declined two to three times faster in elderly adults with low blood levels of the vitamin compared to those with adequate vitamin D levels, and that older people who took vitamin D supplements were less likely to develop dementia.
Vitamin D is sometimes called the sunshine vitamin because it is produced in the skin upon exposure to sunlight. One way to raise blood levels of the vitamin is to spend at least 15 to 20 minutes in the sun each day. The vitamin has long been known for its bone-strengthening properties; that’s one reason it is added to milk and cereals. Fatty fish such as salmon and mackerel also contain high levels of vitamin D.
Vitamin D also influences sleep quality and sleep-wake cycles. Deficiencies of the vitamin have been tied to insomnia and more awakenings during the night. Sleep problems have likewise been shown to increase the risk of Alzheimer’s disease. Differences in sleep patterns were not examined in this study, although 98 percent of participants were poor sleepers.
The findings underscore the importance of identifying vitamin D deficiencies, which are especially common in older men and women. Your doctor can check your levels during a routine blood test and may recommend you take a daily vitamin D supplement. It’s important not to take too much, though. The vitamin is stored in fat, and excessive levels can build up and cause irregular heartbeats and other serious side effects.
By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by Eric Schmidt, Ph.D., Fisher Center for Alzheimer’s Research Foundation at The Rockefeller University.
Source: Sirui Zhou, Paul Sudeshna, Lynn Marie Trotti, et al: “Vitamin D supplement intake is associated with better cognition in persons with sleep disturbance and mild cognitive impairment.” Sleep Medicine, October 2026
