A prospective observational study in the US found that vitamin D deficiency is associated with a substantially increased risk of all-cause dementia and Alzheimer disease. The study included 1658 elderly ambulatory adults free from dementia, cardiovascular disease, and stroke between 1992–1993 and 1999 with a mean follow-up of 5.6 years. 171 participants developed all-cause dementia, including 102 cases of Alzheimer disease. The risk of all-cause dementia and Alzheimer disease markedly increased in participants who were severely vitamin D deficient (serum 25-hydroxyvitamin D<25 nmol/L) and deficient (≥25 to <50 nmol/L) compared to participants with sufficient concentrations (≥50 nmol/L). The risk was adjusted for age, sex, body mass index, smoking status, season of blood sampling, educational attainment, alcohol intake, and presence of depressive symptoms. The results are consistent with past studies that low levels of vitamin D in circulation are associated with increased likelihood of cognitive impairment and dementia. Source: http://www.neurology.org/美国一项前瞻性观测研究发现，维生素D缺乏与各种原因的痴呆和阿尔茨海默病的风险大幅增加有关。该研究包括1992-1993年至1999年间1658名非卧床的老人且无老年痴呆症，心血管病和中风，平均随访5.6年。 171名参加者发生了各种原因的痴呆症，其中包括102例阿尔茨海默病。与具有足够浓度维生素D者（血清25 – 羟维生素D≥50纳摩尔/升）相比，各种原因的痴呆和阿尔茨海默病的风险在严重的维生素D缺乏者（<25 纳摩尔/升）和缺乏者（≥25至<50 纳摩尔/升）中显着增加。风险经过校正年龄，性别，体重指数，吸烟状况，采血的季节，教育程度，饮酒，和抑郁症状存在与否。该结果与已往的研究发现血循环中维生素D水平低与认知障碍和痴呆的可能性增加有关是一致的。来源：http://www.neurology.org/
