Calcium plus vitamin D did not prevent fractures or colorectal cancer in postmenopausal women.

M e t h o d s Design: Randomized placebo-controlled trial (Women’s Health Initiative [WHI] calcium with vitamin D trial). Allocation: Unclear allocation concealment.* Blinding: Blinded (clinicians, participants, and outcome assessors).* Follow-up period: Mean 7 years. Setting: 40 centers in the United States. Participants: 36 282 healthy postmenopausal women 50 to 79 years of age (mean age 62 y) who were also enrolled in the WHI Dietary Modification and Hormone Therapy (HT) trials. Exclusion criteria included expected survival < 3 years, hypercalcemia, kidney stones, corticosteroid use, and calcitriol use. Intervention: Calcium carbonate, 500 mg, and vitamin D3, 200 IU (n = 18 176), or placebo (n = 18 106), twice daily with meals. Personal use of calcium (up to 1000 mg/d), vitamin D (up to 1000 IU/d), bisphosphonates, and calcitonin was allowed. 52% of women were taking HT at baseline. Outcomes: Hip, wrist, vertebral, and total fractures; bone mineral density (BMD) (in a subgroup of 2431 women); colorectal cancer; death; and adverse effects. Patient follow-up: 99% (intention-to-treat analysis).