after exposure to 1,25(OH)2D (50). Whereas some studies have found a relationship between dietary vitamin D intake (22) or metabolite levels (30) only in ER-positive tumors, others have observed stronger protection for ER-negative tumors (28) (see Fig. 2). Additional studies in diverse populations are needed to deter-
mine if the vitamin D-breast cancer relationship varies by age, ethnicity, and tumor characteristics.