Obese and overweight people are more likely to develop colon polyps, a possible precursor to cancer, than slimmer people, according to an international study.
Previous studies have made the connection between obesity and colon cancer, a link recognised by the US National Cancer Institute. But the current study, which appeared in the American Journal of Gastroenterology, is the first to point to a higher risk of colon polyps - also known as adenomas - in heavy people.
"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 Hutan Ashrafian from Imperial College, London, who co-authored the study.
Ashrafian and his colleagues analysed data from 23 studies involving more than 100,000 people across the United States, 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 Organisation (WHO) 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 while two large studies used self-reported questionnaires.
Overall, researchers found that 22 percent of overweight and obese people had colon polyps, compared to 19 percent in people of normal weight. 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 Ashrafian, who with his fellow authors recommended timely colon cancer screening for overweight and obese people.
The findings couldn't say whether obesity causes polyps by itself, but if it does, that may be bad news for a world where obesity is on the rise.
According to the World Health Organisation, about 500 million people world-wide are obese. Colon cancer killed more than half a million people world-wide in 2008, WHO figures show.