NEW YORK (Reuters Health) - Men who gain weight during adulthood -- even those who are not considered to be overweight based on their body mass index -- are at increased risk of colon cancer, according to data from the prospective Health Professionals Follow-Up Study.

Nearly one third of all colon cancers diagnosed over an 18-year period were attributed to having a BMI greater than 22.5 - the middle of the normal BMI range (18.5 - 24.9), Dr. Lau Caspar Thygesen and fellow researchers report in the International Journal of Cancer.

Although being overweight or obese is consistently identified as risk factors for colon cancer, findings with regard to weight change in later life have been contradictory, the researchers note. They belief that because of the way their study was designed, the current analysis is less subject to misclassification.

The patients included 46,349 men between the ages of 40 and 75 years who did not have cancer or ulcerative colitis at study enrollment in 1986. Information on medical history, lifestyle factors, weight, and diet was updated every 2 to 4 years until 2004.

Men with an average BMI above 22.5 had a significant increased risk of colon cancer compared with those with an average BMI between 20 and 22.5, Thygesen, at Denmark's National Institute of Public Health in Copenhagen, and his associates report. The risk was more than doubled among those with a BMI greater than 30, which is consider obese.

The authors estimate that for every 10 pounds gained in the prior 2-4 years, the risk increased by 14 percent. Similarly, for every 10 pounds of weight gained per 10 years since age 21, the risk increased by 33 percent. By contrast, weight at age 21 was not associated with risk.

These findings, the investigators conclude, "support public health interventions to avoid weight gain for prevention of colon cancer."

SOURCE: International Journal of Cancer, September 2008.

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