Level 2: Mid-level evidence
The risk of cancer was evaluated as a secondary outcome in a randomized trial of 1,024 healthy, community-dwelling, postmenopausal women older than 55 years in rural Nebraska (Am J Clin Nutr. 2007;85:1586-1591). The subjects were randomly assigned to receive 1,400-1,500 mg of supplemental calcium/day alone, supplemental calcium plus 1,100 IU vitamin D3/day, or placebo. Almost half (46%) of 543 women received estrogen for ≥60 months during the study. Mean adherence, defined as taking at least 80% of assigned doses, was 85.7% for the vitamin D component and 74.4% for the calcium component.
The rates of any cancer diagnosis in years 1-4 were 6.9% in the placebo group vs. 3.8% in the calcium-alone group vs. 2.9% in the group receiving calcium plus vitamin D (P=.063 for calcium alone vs. placebo, NNT 33; P=.013 for calcium plus vitamin D vs. placebo, NNT 25). Comparing placebo vs. calcium alone vs. calcium plus vitamin D for diagnoses of specific cancers, 8 vs. 6 vs. 5 had breast cancer; 2 vs. 0 vs. 1 had colon cancer; 3 vs. 3 vs. 1 had lung cancer; 4 vs. 4 vs. 2 had leukemia, myeloma, or lymphoid malignancy; 0 vs. 2 vs. 1 had uterine cancer; and 3 vs. 2 vs. 3 had another type of cancer. The rates of cancer diagnosis in years 2-4 were 6.8% with placebo vs. 3.6% with calcium alone vs. 2% with vitamin D plus calcium.