Animal and in vitro experiments suggest that vitamin D is neuroprotective.9,12,13 However, several small clinical studies provide equivocal evidence linking low serum 25- hydroxyvitamin D (25[OH]D) levels to cognitive dysfunction.14-20 No cross-sectional association between serum 25(OH)D levels and verbal memory was observed in older adults from the Third National Health and Nutrition Examination Survey.21 However, cross- sectional associations between 25(OH)D levels and cognitive dysfunction in older adults were observed using data from the Health Survey for England,22 the European Male Aging Study,23 and the Nutrition and Memory in Elders Study.24 Vitamin D supplementation studies have reported improved attention and reaction times after 6 months in 139 ambulatory participants with a history of falls,25 and a small improvement in clock drawing performance, though not verbal fluency, over 4 weeks in 25 nursing home residents who were 25(OH)D deficient at baseline.26