Taking vitamin D supplements may help ward off dementia, according to a new, large-scale study with 12,388 participants who were dementia-free when they signed up.

To examine the vitamin's association for participants with a mean age of 71, researchers at the University of Calgary's Brain Institute in Canada and the University of Exeter in the UK partnered with the US National Alzheimer's Coordinating Center.

Of the group, 37 percent (4,637) took vitamin D supplements.

The team found that it was associated with 40 percent fewer dementia diagnoses in the group who took supplements.

Across the entire sample, 2,696 participants progressed to dementia over ten years; amongst them, 2,017 (75%) had no exposure to vitamin D throughout all visits prior to dementia diagnosis, and 679 (25%) had baseline exposure.

They also found the vitamin linked to living dementia-free for longer periods.

Professor Zahinoor Ismail, of the University of Calgary and University of Exeter, who led the research, said, "We know that vitamin D has some effects in the brain that could have implications for reducing dementia, however so far, research has yielded conflicting results.

"Our findings give key insights into groups who might be specifically targeted for vitamin D supplementation. Overall, we found evidence to suggest that earlier supplementation might be particularly beneficial, before the onset of cognitive decline."

While Vitamin D was effective in all groups, the team found that effects were significantly greater in females, compared to males.

Previous research has found that insufficient levels of vitamin D are linked to higher dementia risk. Vitamin D is involved in the clearance of amyloid in the brain, the accumulation of which is one of the hallmarks of Alzheimer's disease. Studies have also found that vitamin D may provide help to protect the brain against build-up of tau, another protein involved in the development of dementia.

The effects of vitamin D were also significantly greater in people who did not carry the APOEe4 gene, known to present a higher risk for Alzheimer's dementia, compared to non-carriers. The authors suggest that people who carry the APOEe4 gene absorb vitamin D better from their intestine, which might reduce the vitamin D supplementation effect. However, no blood levels were drawn to test this hypothesis.

"We now need clinical trials to confirm whether this is really the case," said Exeter's Dr. Byron Creese, who co-authored the study published in Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring. "The ongoing VitaMIND study at the University of Exeter is exploring this issue further by randomly assigning participants to either take vitamin D or placebo and examining changes in memory and thinking tests over time."

The VitaMIND study is run via PROTECT, an online study open to people aged 40 and over. In PROTECT annual questionnaires on detailed lifestyle factors combine with cognitive testing, to determine what keeps the brain sharp in later life. To find out more or to sign up, visit their website. In Canada, the associated CAN-PROTECT study on aging, in people over 40 additionally focus on caregiving in dementia.

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