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Researchers at the University of Calgary in Canada and the University of Exeter in the UK explored the relationship between vitamin D supplementation and dementia in more than 12,388 participants of the US National Alzheimer’s Coordinating Center.
The partcipants had a mean age of 71 and were dementia-free when they signed up. Of the group, 37 per cent (4,637) took vitamin D supplements.
The study, published in the journal Alzheimer’s & Dementia: Diagnosis, Assessment & Disease Monitoring, found that taking vitamin D was associated with living dementia-free for longer.
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Across the entire sample, 2,696 participants progressed to dementia over ten years; amongst them, 2,017 (75 per cent) had no exposure to vitamin D throughout all visits prior to dementia diagnosis, and 679 (25 per cent) had baseline exposure.
”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,” said Professor Zahinoor Ismail, of the University of Calgary and University of Exeter, who led the research.
”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,” Ismail said.
While Vitamin D was effective in all groups, the researchers found that effects were significantly greater in females, compared to males.
Similarly, effects were greater in people with normal cognition, compared to those who reported signs of mild cognitive impairment — changes to cognition which have been linked to a higher risk 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 study 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 vessels were drawn to test this hypothesis.
Previous research has found that low 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.