By Patrick Holford
Taking vitamin D supplements may help ward off dementia, according to a new, large-scale study involving over twelve thousand dementia-free 70+ year olds in the US. More than a third (37%) took supplements of vitamin D. After adjusting for baseline age, sex, education, race, cognitive diagnosis, depression, and APOE4 status, exposure to prescribed vitamin D supplements was associated with 40% lower incidence of dementia during a ten-year period.
The study, carried out by researchers from the University of Calgary’s Hotchkiss Brain Institute in Canada and the University of Exeter in the UK, has been published in the journal Alzheimer’s & Dementia. The team found that taking vitamin D was associated with living dementia-free for longer, and they also found 40 per cent fewer dementia diagnoses in the group who took supplements.
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.”
One of the problems in relation to vitamin D and cognition is the use of variable amounts of vitamin D, and the lack of reporting regarding blood levels at baseline and conclusion of trials. This study has the same issue. We do not know the dose taken nor the starting and end blood levels of those supplementing or not.
A review by Dr William Grant, Director of Sunlight, Nutrition and Health Research Center, who is the expert on our Scientific advisory Board shows that the higher the blood level of vitamin D (25-hydroxyvitamin D [25(OH)D] is the form measured in the blood serum) the lower is the risk of developing Alzheimer’s as well as dementia in general. The mechanisms identified as potentially explaining its benefit include reduced brain aging, cellular senescence, mitochondrial dysfunction and oxidative stress as well as higher high-density lipoprotein (HDL). Observational study findings indicate that blood levels above 30 ng/mL (75 nmol/L) reduce dementia risk by about 40% and Alzheimer’s risk by about 30% compared to those with blood levels below 12 ng/mL (30 nmol/L) which is broadly consistent with the scale of benefit reported in this trial. You can read Dr William Grant’s full review entitled “The role of vitamin D in reducing risk of Alzheimer’s disease” here.
“In this study, while Vitamin D was effective in all groups, the team found that the beneficial 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.
Dr William Grant says “It is unlikely that vitamin D supplementation is of much use for treating advanced stages of these diseases, although it would be useful in reducing risk of other vitamin D-sensitive adverse health outcomes.” Overall, he says “The evidence regarding vitamin D satisfies the criteria for causality in a biological system for reducing risk of cognitive function, Alzheimer’s and vascular dementia. Thus, vitamin D supplementation can be recommended as an additional way to reduce risk of these diseases. It should also be useful for reducing the rate of progression of these diseases.”
The mechanism(s) for explaining the beneficial effects of vitamin D are not yet clear, however one interesting finding was that 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 APOE4 gene absorb vitamin D better from their intestine, which might reduce the vitamin D supplementation effect due to higher baseline vitamin D levels. However, no blood levels were drawn to test this hypothesis.
Co-author Dr Byron Creese, at the University of Exeter, said: “Preventing dementia or even delaying its onset is vitally important given the growing numbers of people affected. The link with vitamin D in this study suggests that taking vitamin D supplements may be beneficial in preventing or delaying dementia, but we now need clinical trials to confirm whether this is really the case. 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.”
At Food for the Brain those taking the Cognitive Function Test also answer questions about their use, and level of vitamin D, if known. We hope, soon, to start offering vitamin D testing to further research the effects of vitamin D in relation to cognitive decline to be able to track progress both cognitive changes against vitamin D blood levels and intake, to help determine an optimal daily intake or blood level. We are also working with the charitable Grassroots Health Nutrient Research Institute who have tested thousands of people’s blood vitamin D level and are now encouraging them to take Food for the Brain’s Cognitive Function Test. You can join their Vitamin D action group here.
Listen to Patrick Holford’s podcast explaining the role of vitamin D in Alzheimer’s disease here.