Higher intake of calcium and vitamin D has been associated with a reduced risk of colorectal cancer in epidemiologic studies.
It has also been associated with a reduced risk of polyp recurrence in polyp-prevention trials.
However, there is a lack of randomized-trial evidence that calcium with vitamin D supplementation is beneficial in the primary prevention of colorectal cancer.
Dr Jean Wactawski-Wende and colleagues conducted a randomized, double-blind, placebo-controlled trial.
The research team included 36,282 postmenopausal women from 40 Women's Health Initiative centers over a 7-year period.
Out of these, 18,176 women received 500 mg of elemental calcium as calcium carbonate with 200 IU of vitamin D3 twice daily.
The researchers gave 18,106 women a matching placebo.
|Tumor characteristics were similar in the 2 groups|
|New England Journal of Medicine|
The incidence of pathologically confirmed colorectal cancer was the designated secondary outcome.
Baseline levels of serum 25-hydroxyvitamin D were assessed in a nested case-control study.
The team found that the incidence of invasive colorectal cancer did not differ between women assigned to the supplementation or placebo.
The researchers also found that the tumor characteristics were similar in the 2 groups.
The frequency of colorectal-cancer screening and abdominal symptoms was similar in the 2 groups.
The team observed no significant treatment interactions with baseline characteristics.
Dr Jean Wactawski-Wende's team concluded, “Daily supplementation of calcium with vitamin D for 7 years had no effect on the incidence of colorectal cancer among postmenopausal women.”
“The long latency associated with the development of colorectal cancer, along with the 7-year duration of the trial, may have contributed to this null finding.”
“Ongoing follow-up will assess the longer-term effect of this intervention.”