Grant WB. Sunlight, Nutrition, and Health Research Center (SUNARC), P.O. Box 641603, San Francisco, CA 94164-1603, USA. The understanding of the role of vitamin D in maintaining optimal health has advanced sharply in the past two decades. There is mounting evidence for beneficial roles for vitamin D in reducing the risk of bone diseases and fractures, many types of cancer, bacterial and viral infections, autoimmune diseases, and cardiovascular diseases. Recently, several reports have also been published regarding the role of vitamin D in neuroprotection. This article develops the hypothesis that vitamin D can reduce the risk of developing dementia, presenting the evidence from observational and laboratory studies. The observational evidence includes that low serum 25-hydroxyvitamin D [25(OH)D] has 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 dementia. The laboratory evidence includes several findings on the role of vitamin D in neuroprotection and reducing inflammation. Although this evidence is supportive, there do not appear to be observational studies of incidence of dementia with respect to prediagnostic serum 25(OH)D or vitamin D supplementation. Such studies now appear to be warranted. PMID: 19494440 [PubMed - in process]
You can find lots of information about vitamin D at: http://www.vitamindcouncil.org/ They are true believers but even if you believe half of what they say (which is about where I am) it is pretty significant. My husband's neurologist told him to spend time in the sun, but he doesn't. I take 2000 mg of vitamin D on days when I'm not in the sun. I did get my doctor to check my level recently and it was 40--the doctor thought that fine but the Vitamin D council folks think it should be even higher.
Since we live in the north (Maine), we have both been taking fairly good sized doses of Vit D for a long time. Our levels are fine, so I guess that doesn't work, at least for my wife.