D for Dementia: Study Shows the Sunshine Vitamin May Reduce Dementia by 40%

Vitamin D

Getting enough vitamin D on a daily basis is associated with a lower risk of dementia and living dementia-free for longer. Photo: Flashpop/Getty Images

There’s no magic pill to prevent dementia but there is something that may ward off or delay it, according to a new study.

Best of all, you can buy this protection over the counter at the pharmacy. You can even get it by taking a walk in the sunshine or by eating a tuna sandwich. 

Getting enough vitamin D on a daily basis is associated with a lower risk of dementia and living dementia-free for longer.

Researchers from the University of Calgary and the University of Exeter in England found 40 per cent fewer dementia diagnoses over 10 years in the group who took vitamin D supplements.

The large-scale study was published this month in the journal Alzheimer’s & Dementia: Diagnosis, Assessment & Disease Monitoring. The research looked at associations between vitamin D supplementation and dementia in 12,388 dementia-free persons from the U.S. National Alzheimer’s Coordinating Center.

The beneficial effects of supplementing with vitamin D were significantly greater in females, compared to males, the scientists found. Among women, there were 50 per cent fewer dementia diagnoses in the group who took vitamin D supplements. The reason may be associated with the effects of estrogen and estrogen deficiency, suggests study author Dr. Zahinoor Ismail, clinician scientist and professor of Psychiatry, Neurology, Epidemiology and Pathology at the University of Calgary and chair of the Canadian Conference on Dementia.

“Estrogen activates vitamin D,” he explains. “We postulate that in the subgroup of women, estrogen deficiency may potentiate or exacerbate vitamin D deficiency.”

Delaying Dementia


The effects of supplementation were also greater in people with normal cognition, compared to those who reported signs of mild cognitive impairment.

“It may be that vitamin D supplementation early on worked better at preventing disease-related changes than if taken when there were signs of change already,” says Ismail. 

This new study supports previous research, which found that low levels of vitamin D are linked to higher dementia risk. 

The University of Calgary study was observational, however. While the research strongly suggests that vitamin D plays a significant role in preventing dementia, there has been no randomized controlled clinical trial investigating whether supplementation with vitamin D can prevent dementia over the long term.

There is evidence, however, that vitamin D “reduces inflammation and oxidative stress throughout the body, including in the brain,” says Ismail. vitamin D, he explains, “reduces some of the background mechanisms that contribute to poor brain health and poor body health in general.”

As well, he says previous studies have shown that vitamin D can reduce the creation of the beta amyloid plaques and amyloid-mediated formation of tau that are hallmarks of Alzheimer’s.

Your Daily Dose


According to Ismail, the beneficial effect of vitamin D can be achieved by following the Health Canada recommendation: Adults older than 50 years are advised to take a supplement of 600 IU daily, while 800 IU daily is recommended for adults older than 70 years.

“You don’t want to take more than what’s recommended,” advises Ismail. “Those are informed guidelines based on evidence.”

He adds, “Too much vitamin D can adversely affect bone health. However, there are individual differences and people with darker skin are much more likely to be vitamin D deficient, which is an important consideration.”

Both vitamin D2 and vitamin D3 supplements are sold over the counter.

Vitamin D3 comes from animal sources, while vitamin D2 comes from plants. Both forms of the vitamin are effective but some studies have shown that vitamin D3 increased vitamin D levels in the body better than vitamin D2. However, vitamin D2 is available in higher doses and may be less expensive.

Vitamin D is also found in some foods, including eggs, liver and oily fish, such as tuna, salmon, sardines and foods fortified with vitamin D, such as dairy and plant milks and orange juice. But, it’s difficult to get the recommended daily amount from food alone and exposure to the sun is not reliable or, if overdone, safe.


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