David Llewellyn states that he and his colleagues were able to chart with greater accuracy which levels of Vitamin D were relevant to the risk for dementia and Alzheimer’s Disease. Measurements of 25-hydroxyvitamin D [25(OH)D] were classified as severely deficient if < 25 nmol/L, deficient if 25 to 50 nmol/L. Development of Alzheimer’s Disease or any type of dementia was significantly higher in subjects with severely deficient or deficient levels of vitamin D. According to their multi-variant plot charts, the risk of all-cause dementia and Alzheimer’s Disease is “markedly increased” when 25(OH)D levels are bellow 50 nmol/L.
Reference: Littlejohns TJ, Henley WE, Lang IA, et al. Vitamin D and the risk of dementia and Alzheimer disease. Neurology 2014: Published online before print August 6, 2014, doi: 10.1212/WNL.0000000000000755 Neurology 10.1212/WNL.0000000000000755