Obese and overweight people are more likely to develop colon polyps, according to a new review of past research.
"Because there is a known association between obesity and cancer, there is a logical extension to expect a connection between obesity and the step before cancer, which is adenoma," said Dr Hutan Ashrafian from Imperial College, London, who co-authored the study.
How the study was done
Dr Ashrafian and his colleagues analysed data from 23 studies involving more than 100 000 people across the U.S., Asia and Europe, looking at the relationship between polyps and body mass index.
All the studies followed World Health Organisation guidelines that define people with a BMI over 25 as overweight and above 30 as obese. In most studies, polyps were identified during colonoscopy. Questionnaires were used in two large studies.
Overall, 22% of overweight and obese people had colon polyps, compared to 19% of people of normal weight, and the polyp risk grew with increasing BMI.
"The findings suggest that obesity may be having an effect (on cancer development) much earlier than we thought," said Dr Ashrafian.
In a report online in the American Journal of Gastroenterology, the authors recommend timely colon cancer screening among overweight and obese people.
The U.S. Preventative Services Task Force, a government-funded expert panel, recommends colon cancer screening for people ages 50 to 75. In the UK, screening for colon cancer is offered by the National Health Service from age 60 to 69.
The new study points to a need for screening that specifically targets obese people, said Dr Joseph Anderson from Dartmouth in Hanover, New Hampshire, who was not involved in the study.
There are different ways to screen people, and if a person is obese, they are at higher risk and should have a full colonoscopy, he added. Obese people tend to have adenomas in the upper part of the colon, where sigmoidoscopy doesn't reach, said Dr Anderson, who has written an editorial on the study.
But Dr Michael Leitzman, who has researched obesity and adenomas, urges caution.
BMI didn't seem to be linked to faster development of cancer once colon polyps were present, so changing screening practices doesn't seem to be necessary, said Dr Leitzman, from University Hospital Regensburg in Germany.
Still, both Dr Anderson and Dr Leitzman agreed that the study had combined the best of previous research on obesity and colon polyps, and strengthened evidence of the link between obesity and colon cancer.
Dr Anderson did, however, note that the study didn't account for diabetes as a potentially confounding factor. Because of such uncertainties, the data can't prove that losing weight reduces the risk of developing polyps, or reverses the progression of cancer development.
(Reuters, July 2012)
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