Williams JA, Sink KM, Tooze JA, Atkinson HH, Cauley JA, Yaffe K, Tylavsky FA, Rubin SM, Simonsick EM, Kritchevsky SB, Houston DK. Low 25-hydroxyvitamin D concentrations predict incident depression in well-functioning older adults: the health, aging, and body composition study. J Gerontol A Biol Sci Med Sci. 2015 Jun; 70(6):757-63.