Although less than 10 percent become cancerous, most colon cancers are thought to develop from polyps. Previous studies have made the connection between obesity and colon cancer – a link recognized by the National Cancer Institute – but the new study is the first to point to a higher risk of adenomas in heavy people. By focusing on “precancerous” cell changes, researchers were hoping to shed more light on whether cancer screening recommendations should take a person’s weight into account. “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. The findings can’t say whether obesity causes polyps by itself. But if it does, that could be bad news for a world where obesity is on the rise. According to the World Health Organization, about 500 million people worldwide are obese; colon cancer killed more than half a million people worldwide in 2008, the most recent figures from the WHO show. For the new research, Ashrafian and his colleagues analyzed 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, or BMI, a measure of weight relative to height. All the studies followed World Health Organization guidelines that define people with a BMI over 25 as overweight and above 30 as obese. In most studies, polyps were identified during colonoscopy procedures in which a flexible tube tipped with a camera is guided though the rectum and into the colon. Self-reported questionnaires were used in two large studies. Overall, researchers found that 22 percent of overweight and obese people had colon polyps, compared to 19 percent in people of normal weight, and the polyp risk grew with increasing BMI.
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