Hansen JG, Tang W, Hootman KC, Brannon PM, Houston DK, Kritchevsky SB, Harris TB, Garcia M, Lohman K, Liu Y, de Boer IH, Kestenbaum BR, Robinson-Cohen C, Siscovick DS, Cassano PA. Genetic and environmental factors are associated with serum 25-hydroxyvitamin D concentrations in older African Americans. J Nutr. 2015 Apr; 145(4):799-805.