The notion that vitamin D deficiency is associated with a substantially increased risk of all-cause dementia and Alzheimer disease was confirmed by the results of the largest study of its kind.
David J. Llewellyn, PhD, of the University of Exeter Medical School in the United Kingdom and colleagues from other centers looked at blood levels of vitamin D, including vitamin D from food, supplements, and sun exposure. They studied 1658 ambulatory adults older than 65 years free from dementia, cardiovascular disease, and stroke who participated in the US population–based Cardiovascular Health Study between 1992–1993 and 1999.
Serum 25-hydroxyvitamin D (25[OH]D) concentrations were determined by liquid chromatography-tandem mass spectrometry from blood samples collected in 1992–1993. Incident all-cause dementia and Alzheimer disease status were assessed during follow-up using National Institute of Neurological and Communicative Disorders and Stroke/Alzheimer’s Disease and Related Disorders Association criteria.
During a mean follow-up of 5.6 years, all-cause dementia developed in 171 participants, including 102 cases of Alzheimer disease.
There was a 53% increased risk of dementia in participants with low levels of vitamin D and a 125% increased risk in those who were severely deficient compared with participants who had normal levels of vitamin D.
The chances of Alzheimer disease were nearly 70% greater in participants with lower levels of vitamin D and 120% greater in those who had severe deficiency.
The results remained the same after researchers adjusted for other factors that could affect risk of dementia, such as education, cigarette smoking, and alcohol consumption.
“The results were surprising—we actually found that the association was twice as strong as we anticipated,” said Dr Llewellyn. “Our findings are very encouraging, and even if a small number of people could benefit, this would have enormous public health implications given the devastating and costly nature of dementia."
The study was published in the August 6, 2014, online issue of Neurology, the medical journal of the American Academy of Neurology.