Elevated calcium levels were associated with an increased risk of BC (inverse variance weighting: [OR] = 1.295, 95% [CI] = 1.062–1.578, P = .011), while higher sex hormone-binding globulin levels were linked to a decreased risk (inverse variance weighting: OR = 0.857, 95% CI = 0.741–0.991, P = .037). This evidence concerns the gene SHBG and breast cancer.