April 22, 2026
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, according to a new report. The study found that as they approached age 60, those with low vitamin D levels around age 40 tended to have higher brain levels of tau, a toxic protein that is a hallmark of Alzheimer’s disease. Buildup of tau can lead to the formation of spaghetti-like tangles that choke off healthy brain cells, speeding the onset of dementia.
“These results suggest that higher vitamin D levels in midlife may offer protection against developing these tau deposits in the brain, and that low vitamin D levels could potentially be a risk factor that could be modified and treated to reduce the risk of dementia,” said study author Martin David Mulligan, of the University of Galway in Ireland.
The authors stressed that more study is needed to better understand the relationship between vitamin D levels and brain health but noted that maintaining healthy vitamin D levels in midlife could be one way to help lower your risk of developing Alzheimer’s disease years later. “Mid-life is a time where risk factor modification can have a greater impact,” Dr. Mulligan said.
For the study, researchers assessed vitamin D blood levels in 793 men and women whose average age was 39. None had serious memory problems or other signs of dementia. About a third had low levels of vitamin D, defined in this study as less than 30 nanograms per milliliter of blood. (Vitamin D levels generally decrease with age, and in older adults, low levels are generally considered to be under 20 nanograms per milliliter.) About 5 percent of study volunteers were taking vitamin D supplements.
Sixteen years later, when participants were in their mid-50s, they had PET scans to assess brain health. Those with higher vitamin D levels around age 40 tended to have lower levels of tau buildup in later middle age. There was no relationship between vitamin D levels in early midlife and the buildup of another toxic protein called beta-amyloid that clumps together to form the telltale plaques of Alzheimer’s disease. The findings were published in the journal Neurology Open Access.
The study showed only an association between low vitamin D levels and higher levels of tau in the brain and cannot prove cause and effect. But previous studies, most conducted in older adults, have found that low levels of vitamin D are linked to higher dementia risk, and that taking measures to assure you have adequate levels of vitamin D may help to keep the brain in good working order.
Vitamin D, which promotes bone health, is sometimes called the “sunshine vitamin” because it is produced in the skin upon exposure to sunlight. People living in northern latitudes, particularly those with dark complexions, may be especially prone to vitamin D deficiency during the winter months, when sunlight levels are low. Your doctor can check your levels during a routine blood test.
The best way to help assure healthy vitamin D levels is to spend limited time in the sun (dermatologists generally recommend limiting exposure to 15 to 20 minutes a day) so the skin can make the vitamin. It is also important to eat foods rich in the vitamin, like fatty fish such as salmon, mackerel and sardines; consumption of fish has been linked to a lower risk of Alzheimer’s disease. Vitamin D is also often added to milk, cereals and other foods, though it may be hard to achieve healthy levels via foods alone, especially in the winter months. Vitamin D supplements can also help if you are low in the vitamin, though don’t take too much, as excess can build up in the body and lead to heart rhythm disorders and other problems.
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: Martin David Mulligan; Matthew R. Scott; Qiong Yang; et al: “Association of Circulating Vitamin D in Midlife With Increased Tau-PET Burden in Dementia-Free Adults.” Neurology Open Access, April 1, 2026
