Vitamin D in Older Adults: The Need to Specify Standard Values with Respect to Cognition

Besides its classical function of bone metabolism regulation, vitamin D exhibits multiple biological targets mediated by its nuclear hormone receptor, the vitamin D receptor (VDR) (Holick, 2007; Kalueff and Tuohimaa, 2007; Annweiler et al., 2010a, 2011b). Specific actions on target organs such as the central nervous system (CNS) have been described, providing evidence for a neurosteroid action of vitamin D (Kalueff and Tuohimaa, 2007; Annweiler et al., 2010a). Consistently, older adults with lower serum 25-hydroxyvitamin D (25OHD) concentrations exhibit more often and more severe cognitive decline (Annweiler et al., 2009, 2013a,b; Balion et al., 2012; Etgen et al., 2012). At that point, an important issue to be clarified is to determine what concentration of 25OHD is associated with adverse effects in the brain.