This study overcomes limitations of existing genetic association studies that may report spurious results due to lack of control for genetic ancestry, skin reflectance, collection of blood specimens during summer months, or the use of assays that do not distinguish 25(OH)D2 and 25(OH)D3. The advantages of this study are: 1) a matched design that incorporates temporal assessment of vitamin D metabolism, 2) genetic Ancestry Informative Markers (AIMs), 3) melanin skin index, 4) a sensitive and reliable assay for four serum vitamin D metabolites, and 5) functional molecular assays related to specific genetic polymorphisms.