From The New York Times, August 14, 2014:
"Low vitamin D is associated with an increased risk for Alzheimer’s disease and other forms of dementia, according to a new report, though whether low vitamin D is a cause of the disorders remains unknown.
The scientists measured blood levels of vitamin D in 1,658 men and women, average age of 73, without dementia at the start of the study. Over an average follow-up of more than five years, 171 developed dementia.
The study, published online in the journal Neurology, controlled for many dementia risk factors — including age, education, sex, body mass index, smoking, alcohol use, diabetes and hypertension. It found that compared with those who had vitamin D levels of 50 or more nanomoles per liter, those with levels of 25 to 50 had a 53 percent increased risk for all-cause dementia and a 69 percent increased risk for Alzheimer’s disease. People with readings of 25 or less were more than twice as likely to have Alzheimer’s or another form of dementia.
There is little agreement on the ideal vitamin D level, but according to the National Institutes of Health, levels below 50 are inadequate.
“These are exciting and suggestive results, but they’re only observational,” said a co-author, Iain A. Lang, a senior lecturer at the University of Exeter. “We can’t say anything about whether people should be supplementing, because that’s beyond the scope of what we looked at.” "