Calcium + vitamin D doesn’t curb colorectal cancer risk
In a large study of postmenopausal women, daily supplementation of calcium with vitamin D for 7 years did not reduce the risk of colorectal cancer, doctors report in The New England Journal of Medicine this week. However, a beneficial effect may be become apparent with longer follow-up, the authors note.
Past studies have linked calcium and vitamin D use with a reduced risk of colorectal cancer and, in polyp-prevention trials, this combination seemed to help prevent polyp recurrence. Whether this dietary intervention could actually help prevent colorectal cancer, however, was unclear.
To investigate, Dr. Jean Wactawski-Wende, from SUNY University at Buffalo in New York, and colleagues assessed the outcomes of 36,282 postmenopausal women who participated in a study in which they received calcium 500 mg with vitamin D 200 IU or matching placebos twice daily for 7 years.
During follow-up, the number of women who developed colorectal cancer was nearly the same in each group, hovering around 161.
Moreover, the tumors that developed in each group were similar in appearance and stage. Likewise, colorectal-cancer screening and abdominal symptoms were comparable in each group.
The investigators reason that the “long latency associated with the development of colorectal cancer, in concert with the 7-year duration of the trial, may have contributed to” the null finding.
In a related editorial, Dr. Michele R. Forman and Dr. Bernard Levin, from the M. D. Anderson Cancer Center in Houston, note that the doses of these substances “may have been too low to achieve the desired effect.”
SOURCE: The New England Journal of Medicine, February 16, 2006
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