Possible Link between Vitamin D Deficiency and Alzheimer's

There are several risk factors for the development of Alzheimer's and vascular dementia. Based on an increasing number of studies linking these risk factors with Vitamin D deficiency, an article in the current issue of the Journal of Alzheimer's Disease suggests that further investigation of possible direct or indirect linkages between Vitamin D and Alzheimer's and vascular dementia is needed.

We face a looming global epidemic of Alzheimer’s as the world’s population ages. Modest advances in therapeutic and preventive strategies that lead to even small delays in Alzheimer’s onset and progression can significantly reduce the global burden of Alzheimer’s

In 2006 the worldwide prevalence of Alzheimer’s was 26.6 million. By 2050, prevalence will quadruple by which time 1 in 85 persons worldwide will be living with Alzheimer’s.

The image depicts the comparison of a normal aged brain (top) and an Alzheimer's patient's brain (bottom). Differential characteristics are pointed out.

Low serum levels of 25-hydroxyvitamin D [25(OH)D] have been associated with increased risk for cardiovascular diseases, diabetes mellitus, depression, dental caries, osteoporosis, and periodontal disease, all of which are either considered risk factors for dementia or have preceded incidence of Alzheimer's and dementia. In 2008, a number of studies reported that those with higher serum 25(OH)D levels had greatly reduced risk of incidence or death from cardiovascular diseases.

Several studies have correlated tooth loss with development of cognitive impairment and Alzheimer's or vascular dementia. There are two primary ways that people lose teeth: dental caries and periodontal disease. Both conditions are linked to low vitamin D levels, with induction of human cathelicidin by 1,25-dihydroxyvitamin D being the mechanism.

There is also laboratory evidence for the role of vitamin D in neuroprotection and reducing inflammation, and ample biological evidence to suggest an important role for vitamin D in brain development and function.

Given these supportive lines of evidence, Dr. Grant suggests that studies of incidence of dementia with respect to prediagnostic serum 25(OH)D or vitamin D supplementation are warranted. In addition, since the elderly are generally vitamin D deficient and since vitamin D has so many health benefits, those over the age of 60 years should consider having their serum 25(OH)D tested, looking for a level of at least 30 ng/mL but preferably over 40 ng/mL, and supplementing with 1000-2000 IU/day of vitamin D3 or increased time in the sun if below those values.

Dr. Grant says, "There are established criteria for causality in a biological system. The important criteria include strength of association, consistency of findings, determination of the dose-response relation, an understanding of the mechanisms, and experimental verification. To date, the evidence includes observational studies supporting a beneficial role of vitamin D in reducing the risk of diseases linked to dementia such as vascular and metabolic diseases, as well as an understanding of the role of vitamin D in reducing the risk of several mechanisms that lead to dementia."

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References:
1. William B. Grant. Does Vitamin D Reduce the Risk of Dementia? Journal of Alzheimer's Disease 17:1.
2. Ron Brookmeyer, et al. FORECASTING THE GLOBAL BURDEN OF ALZHEIMER’S DISEASE. Johns Hopkins University