Unlike other research into the association between vitamin D and dementia, this large study quantified and graded levels of vitamin D deficiency to determine at what point intervention might be warranted.
The topic of vitamin D was once linked only to bone health but a wealth of studies suggest that low levels of vitamin D may be a risk factor for a wide range of age-related diseases, including cancer, hypertension, stroke, and cognitive decline. Recent meta-analyses show low serum vitamin D levels are associated with both Alzheimer disease (AD) dementia and cognitive impairment. The elderly are at risk for progressive vitamin D deficiency and, say some researchers, the risk of cognitive decline increases significantly below a threshold of between 25 and 50 nmol/L of 25-hydroxyvitamin D (25[OH]D).
The current study, published in the August 6 online issue of Neurology, is believed to be the first large, prospective population-based study on the relationship between dementia risk and vitamin D in which dementia was diagnosed by a team of experts.
The study included 1658 elderly ambulatory adults free from dementia, cardiovascular disease, and stroke. During 9317.5 person-years of follow-up, 171 participants developed dementia and 102 developed AD. The risk of developing both was significantly higher in persons who were 25(OH)D deficient (25 nmol/L or greater to less than 50 nmol/L ) or severely deficient (less than 25 nmol/L).
Participants who were severely vitamin D-deficient had about a 122% increased risk for all cause dementia (HR, 2.22; 95% CI, 1.23 - 4.02) compared with those with sufficient vitamin D. Those who were deficient but not severely so had a 51% increased risk (HR, 1.51; 95% CI, 1.06 - 2.16; P = .002) compared with those with sufficient vitamin D.
It is too early to tell doctors to order vitamin D levels on older patients or even to recommend supplementation to prevent dementia-the study authors and the Alzheimer’s Association, a study partner, agree on both points. Also unknown at this stage is the appropriate blood level of vitamin D that might be protective. The AD dementia-vitamin D link is compelling enough, however, to encourage trials that will “dig deep” into whether or not the progression of dementia can be slowed with vitamin D supplementation.
Littlejohns TJ, Henley WE, Lang AI, et al. Vitamin D and the risk of dementia and Alzheimer disease. Neurology. 2014;83:1-9. (Full text)