Can taking vitamin D supplements help prevent dementia?

For the study, the researchers analyzed data from 12,388 people from the National Alzheimer’s Coordinating Center, who were dementia-free at the start of the study. Their average age was 71 years old.

Altogether, 37% of the cohort took at least one of three vitamin D supplements: calcium-vitamin D, cholecalciferol, and ergocalciferol.

In their analyses, the researchers also accounted for demographic, clinical, and genetic variables, such as depression and APOE ε4 status—a gene variant linked to a higher risk of dementia.

After five years, the researchers found that 83.6% of those exposed to vitamin D supplements were alive and dementia-free. The same was true for 68.4% of those not exposed to vitamin D.

Within 10 years, the researchers found that 22% of participants developed dementia, of which 74.8% were not exposed to vitamin D supplements.

Whereas 14.6% of those with vitamin D exposure progressed to dementia, the same was true for 26% of those with no vitamin D exposure.

After adjusting for factors including cognitive diagnosis, depression, and APOE ε4 status, they found that vitamin D exposure was linked to a 40% lower incidence of dementia compared to no exposure.

Women see more benefit

The effects were strongest among women: women exposed to vitamin D were 49% less likely to develop dementia than those without exposure. Vitamin D-exposed men were 26% less likely to develop dementia than non-exposed men.

The researchers also found that depression was linked to a 35% higher incidence of dementia.

While findings were consistent for each vitamin D formulation, they noted that vitamin D supplements had the greatest effects on individuals with normal cognition as opposed to mild cognitive impairment and APOE ε4 non-carriers versus carriers.

Dr. Delma Montoya Monge, assistant professor of geriatric and palliative medicine with McGovern Medical School at UTHealth Houston, who was not involved in the study, told Medical News Today that the findings suggest vitamin D supplementation reduces dementia risk among some patients.

She added that the findings also “remind us that older adults with vitamin D deficiency may be at higher risk of poor health outcomes.”

When asked how vitamin D supplements may be linked to lower dementia incidence, Dr. Dario Zagar, associate professor at Yale School of Medicine, who was not involved in the study, told MNT:

“Prior studies have shown that low vitamin D levels are a risk factor for developing dementia, such as AD [Alzheimer’s disease]. Vitamin D has many functions in the body besides maintaining bone health, which is what most people think of.”

“From the standpoint of memory disorders, vitamin D plays a role in clearing a protein called beta-amyloid, which accumulates in the brain in people with AD. It may also help to protect nerve cells from injury, including from other abnormal proteins that play a role in dementia.”
— Dr. Dario Zagar

Dr. Jacob Teitelbaum, a board-certified internist and author of books including From Fatigued to Fantastic!, who was not involved in the study, said immunity might be involved behind vitamin D’s benefits for dementia:

“My suspicion is that if vitamin D lowers dementia risk, it does so by balancing immunity. It is suspected that amyloid deposition may simply be a response to excess inflammation, being like a ‘band-aid’ that the body puts on brain inflammation. [I]f so, this would account for why women are one-third more likely to get Alzheimer’s.”

Dr. Teitelbaum also touched on the reasons behind the finding that women were more likely to benefit from vitamin D supplements.

“Women are much more prone to autoimmune conditions, being three times more likely to have lupus, rheumatoid arthritis, fibromyalgia, and a host of other immune and autoimmune problems,” he told MNT.

“It is suspected that this is because a woman’s immune system is different from a man’s. A woman has 2 X chromosomes, whereas a man only has one. And much of the genes regulating immunity are on the X chromosome,” he explained.

“So that women were more likely to benefit from vitamin D in the study suggests that it helped balance immunity, and that it was actually taking the vitamin D that caused the benefit,” he noted.

Dr. Jordan Taylor, neurology section chief with the University of Michigan Health-West, who was also not involved in the study, told MNT that the findings are limited due to significant differences between the participants in the two study groups.

He noted that those in the vitamin D supplementation group tended to have more years of education and that fewer identified as Black, and that both factors are linked to lower dementia risk.

He further pointed out that depression and mild cognitive impairment—which some studies suggest are dementia risk factors—were higher in the non-supplementing group.

“Because these variables, which are known to affect the rates/risks of dementia were not controlled, it is difficult to draw clean interpretations from the data,” he said.

“Also, while several formulations of vitamin D were included, the dose of vitamin D supplementation as well as the baseline/follow-up vitamin D blood levels are not reported. This leaves it unclear whether or not a low, normal or high blood level contributes to risk or if evaluating vitamin D levels could be used to assess for adequate ongoing supplementation or initial supplementation need.”
— Dr. Jordan Taylor

Dr. Alvaro Pascual-Leone, Ph.D., chief medical officer of Linus Health and professor of neurology at Harvard Medical School, not involved in the study, stressed that this was not evidence for causality.

“These are important results, but they do not establish true causal evidence. It could be that vitamin D intake is not the reason for the protection from dementia, but rather leads or is linked to some behaviors that, in turn, are the reason for the reduction in dementia risk,” he told MNT.

“For example, people who take vitamin D may be those who overall take better care of themselves and pay greater attention to their health and nutrition, which may then be the reason for the dementia protection,” he said.

Dr. Theodore Strange,chair of medicine at Staten Island University Hospital, who was also not involved in the study, added that the study did not account for important factors, including differences in socioeconomic status, or record for sun exposure, and exposure to other supplements that might have contributed to lower dementia risk.

Given these gaps in data, Dr. Pascual-Leone noted that the results invite larger studies, including a controlled, experimental clinical trial where people are randomized to take vitamin D.

“Also important to remember is that taking too much vitamin D can cause some health problems, so evaluation of the appropriate dose is also needed,” he cautioned.

Dr. David A. Merrill, Ph.D., psychiatrist and director of the Pacific Neuroscience Institute’s Pacific Brain Health Center at Providence Saint John’s Health Center in Santa Monica, California, who was not involved in the study, reiterated that there were many ways to protect the aging brain.

“It’s good that there are randomized trials testing vitamin D, but no single factor will be sufficient to keep the brain intact with aging. We must leave no stone unturned when it comes to optimizing health with aging,” he told MNT.

“Aiming for optimal health may better protect against AD than settling for normal. There are now dozens of health factors we know can reduce risk for AD—patients and doctors need to be curious to check and correct such factors to optimal status. [For example,] having a blood level between 40-80 may be ‘optimal’ for healthy brain aging, which is higher than the lower end of ‘normal’ for laboratory results,” he noted.

“We need multi-factorial analysis and intervention, and the earlier a person starts the better. The best results were seen in this study for persons who began supplementation with normal cognition. An ounce of prevention is worth a pound of cure, as the saying goes.”
— Dr. David A. Merrill