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.
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.
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% said they took a multivitamin regularly (four or more times per week) only in the past, and 19% said they regularly took a multivitamin only recently.
Participants who were regular multivitamin users 10 years before the start of the study had an approximately 30% less risk of developing colorectal cancer. Those who had only recently begun to use multivitamins were not at reduced risk..
This study, together with results from previous studies, provides limited evidence that some component in multivitamins may modestly reduce risk of developing colorectal cancer. The exact component or components of multivitamins that may be protective remain unclear.
Previous studies have linked folic acid to a lower risk of colon cancer in women with a family history of the disease.
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