Wilson VK, Houston DK, Kilpatrick L, Lovato J, Yaffe K, Cauley JA, Harris TB, Simonsick EM, Ayonayon HN, Kritchevsky SB, Sink KM. Relationship between 25-hydroxyvitamin D and cognitive function in older adults: the Health, Aging and Body Composition Study. J Am Geriatr Soc. 2014 Apr; 62(4):636-41.