Taking multivitamins may modestly reduce a person's chances of getting colorectal cancer, but not right away. There is a long interval between the start of taking multivitamins and when the apparent protective effect kicks in, the research team reports in the October 2003 issue of the American Journal of Epidemiology..
These new findings come from the Cancer Prevention Study II Nutrition Cohort, in which researchers examined the relationship between current and past use of multivitamins and the occurrence of colorectal cancer among more than 145,000 predominantly white, middle-aged or elderly adults.
"This study was conducted to follow-up on a report from the Harvard Nurse's Health Study, indicating that prolonged multivitamin use might substantially reduce risk of colon cancer," said Dr. Eric J. Jacobs from the American Cancer Society in Atlanta, Georgia.
At enrollment in 1992-1993, participants provided information on current use of multivitamins. All of the subjects had also provided information on multivitamin use some 10 years earlier in 1982, as part of another study. This allowed the investigators to examine the potential effects of past use of vitamins, without relying on what people recalled. Roughly half of the group reported no multivitamin use, 8 percent said they took a multivitamin regularly (four or more times per week) only in the past, and 19 percent said they regularly took a multivitamin only recently.
During follow-up from 1992 to 1997, 797 cases of colorectal cancer were detected. After adjusting for "health conscious" behaviors, participants who were regular multivitamin users 10 years before the start of the study had an approximately 30 percent less risk of developing colorectal cancer. Those who had only recently begun to use multivitamins "were not at reduced risk," Jacobs said.
"Our study, together with results from previous studies, provides limited evidence that some component in multivitamins may modestly reduce risk of developing colorectal cancer," Dr. Jacobs said. The exact component or components of multivitamins that may be protective remain unclear.
The researcher emphasized, however, that the American Cancer Society does not currently recommend using multivitamins for cancer prevention, as the evidence is insufficient. In contrast, the ACS strongly recommends that all Americans 50 and over get a screening test for colorectal cancer, Dr. Jacobs said. "Colorectal cancer screening has been proven to substantially reduce the risk of dying from colorectal cancer."
Jacobs E.J.; Connell C.J.; Chao A.; McCullough M.L.; Rodriguez C.; Thun M.J.; Calle E.E.
Multivitamin Use and Colorectal Cancer Incidence in a US Cohort: Does Timing Matter?
American Journal of Epidemiology, 01 October 2003, vol. 158, no. 7, pp. 621-628(8).