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Although primary prevention of CRC via dietary measures is controversial, secondary prevention by interrupting the adenoma-carcinoma sequence is possible. One cross sectional study2 and a case control study3 have demonstrated the association between obesity and colorectal adenomas in men2 and women,3 respectively, whereas another study failed to show any association.4 Although cross sectional studies in Japan have demonstrated an association between obesity and colorectal adenomas, all subjects were males and total colonoscopy was performed in only some subjects.5 Colonoscopy is proven to be superior to double contrast barium enema for detection of adenomatous lesions as well as early CRC. We therefore aimed to examine the association between obesity and colorectal polyp by total colonoscopy.
A cross sectional study was conducted on a total of 541 consecutive adult subjects (361 males and 180 females) who attended the University Hospital outpatient clinic with gastrointestinal problems and underwent total colonoscopy, from December 2000 to December 2001. Patients with CRC, colonic obstruction, known inflammatory bowel disease, and a past history of gastrointestinal surgery were excluded. All colonoscopies were performed by experienced endoscopists. Body height and weight were measured, and body mass index (BMI) was calculated as weight (kg) per height (m2). In the present study, we defined BMI ⩾25.0 kg/m2 as “obese” and others as “non-obese”. Standard statistical methods were used and the results were given as mean (SEM). The significance of the difference between the two groups was examined using the χ2 test. Differences with p<0.05 were considered significant. Table 1 shows the characteristics of the obese and non-obese groups.
Age, sex, and body height were not significantly different between the two groups while body weight and BMI were significantly higher in the obese group. Colorectal polyps were found in 57 of 112 obese patients (50.9%) but in only 124 of 429 non-obese patients (28.9%) (p<0.001). Biopsy or polypectomy was performed for all polyps, which were diagnosed as adenomatous polyps by histopathological examination. In common with previous studies,2,3,5 we have clearly demonstrated an association between obesity and colorectal adenomas in Japanese adult patients, performing total colonoscopy in all subjects. In contrast, an inverse relationship between obesity and colorectal adenomas was reported in Western countries.4 However, risk factors for colorectal polyps are not clear. This discrepancy may be due to racial and/or lifestyle differences. As this was a cross sectional study at a single university hospital, prospective multicentre case control studies are needed to demonstrate a close association between obesity and colorectal polyps in the Japanese.
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