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

About one third of all colon cancers diagnosed over an 18-year period were attributed to a BMI greater than 22.5, Dr. Lau Caspar Thygesen and fellow researchers report in the International Journal of Cancer for September.

Although overweight and obesity are consistently identified as risk factors for colon cancer, findings with regard to weight change in later life have been contradictory, the researchers note. They assume that, because of its “purely prospective weight information,” long follow-up, repeated assessments, and adjustment for confounders, the current analysis is less subject to misclassification.

The cohort included 46,349 men aged 40-75 years without cancer or ulcerative colitis at enrollment in 1986. Information on medical history, lifestyle factors, weight, and diet was updated every 2-4 years until 2004.

“Cumulative mean BMI above 22.5 was associated with significantly increased risk of colon cancer compared to BMI of 20-22.5,” Dr. Thygesen, at Denmark’s National Institute of Public Health in Copenhagen, and his associates report.

Compared with this reference, the risk was more than doubled among those with a BMI greater than 30 (multivariate adjusted hazard ratio 2.29).

To minimize bias caused by weight loss due to undiagnosed cancer, the authors examined latency time between updated weight change and colon cancer risk by lagging the follow-up by 2-4 years.

Thus, they estimate that for every 10 pounds gained in the prior 2-4 years, the risk increased by 14% (p = 0.04 for overall trend). Similarly, for every 10 pounds of weight gained per 10 years since age 21, the risk increased by 33% (p = 0.001).

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.”

Int J Cancer 2008;123:1160-1165.