Calcium/vitamin D do not prevent colon cancer (WHI)

Clinical Question: Does supplementation with 1000 mg calcium and 400 IU vitamin D reduce the risk of colorectal cancer in healthy women?

Bottom Line:

A modest dose of calcium and vitamin D does not alter the risk of colorectal cancer in healthy, normal-risk women. (LOE = 1b)

Reference:

Wactawski-Wende J, Kotchen JM, Anderson GL, et al, for the Women’s Health Initiative Investigators. Calcium plus vitamin D supplementation and the risk of colorectal cancer. N Engl J Med 2006;354:684-96.

Study Design:

Randomized controlled trial (double-blinded)

Funding:

Government

Setting:

Population-based

Allocation:

Uncertain

Synopsis:

In this substudy of the Women’s Health Initiative, 36,282 women were randomized to receive either 1000 mg calcium and 400 IU vitamin D per day or placebo. There was no formal screening required as part of the study for colorectal cancer; screening was left to the woman and her personal physician. Cancers were verified using a national cancer surveillance program. The study was adequately powered; it had 83% power to detect an 22% decrease in the incidence of colorectal cancer. The groups were balanced at the start of the study, analysis was by intention to treat, and the number of patients who dropped out or were lost to follow-up was modest (approximately 500 in each group). After a mean of 7 years, there was no difference in the incidence of invasive colorectal cancer (168 vs 154 cases; hazard ratio = 1.08; 95% CI, 0.86 – 1.34). Subgroup analyses revealed no meaningful patterns. Not surprisingly, women in the supplement group had 17% more kidney stones.