Vitamin D (VitD) deficiency is a worldwide epidemic with estimates of 1 billion affected. In addition to the classically known roles of VitD in calcium regulation and bone health, recent studies demonstrated VitD to be an essential/vital neurosteroid hormone playing a wide variety of essential protective and regulatory roles in the brain. This paper reviews much of the mounting evidence of the detrimental effects of VitD deficiency on the brain and the association of many of these common links with Alzheimer's disease (AD). We also discuss the beneficial effects seen from VitD supplementation. Based on this accumulation of studies, we propose that VitD screening should be performed at least in those individuals at risk for VitD deficiency and AD. With appropriate medical counsel, those found to be VitD deficient should be considered for appropriate supplementation.