Researchers followed over 1,500 healthy elderly people for nearly six years and found that those with persistently low levels of vitamin D were up to 2.4 times more likely to develop Alzheimer’s compared to people with normal vitamin D levels. The commonly accepted definition of vitamin D deficiency is a level below 30 nanomoles per liter, although this study used a level below 50 as a threshold.
While this study strengthens the association between low vitamin D and dementia risk, the researchers could not definitively rule out a phenomenon called “reverse causality,” meaning it is possible that low vitamin D levels did not cause the dementia and were associated with an increased risk in certain people for other reasons. If that’s true, then vitamin D may not protect against Alzheimer’s even if low vitamin D levels predict decline.
Read the Cognitive Vitality report on vitamin D for an overview of the evidence surrounding the link between vitamin D levels and dementia.
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