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Re: Obesity as a risk factor for colorectal polyps in Japanese

Dear Editor

Colorectal cancer (CRC) is one of the most common malignant diseases in the developed countries. Recent epidemiological studies suggest that CRC is associated with obesity.[1,2]

Although primary prevention of CRC via dietary measures is controversial, secondary prevention by interrupting the adenoma carcinoma sequence is possible. One cross-sectional [3] and a case-control [4] studies have demonstrated the association between obesity and colorectal adenomas in men [3] and women,[4] respectively, whereas other study failed.[5] Although cross-sectional studies in Japan have demonstrated the association between obesity and colorectal adenomas, all subjects were males and total colonoscopy was not performed except only some subjects.[6] 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 appeared directly to the University Hospital outpatient clinic with gastrointestinal problems, and was underwent total colonoscopy from December 2000 to December 2001. Patients with CRC, colonic obstruction, known inflammatory bowel disease, and past history of gastrointestinal surgery were excluded. All colonoscopies were performed by experienced endoscopists. The 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 ³ 25.0 kg/m² as "obese" and others as "non-obese". Standard statistical methods were used and the results were shown as mean ± standard error. The significance of the difference between two groups was examined with c2 test. Differences with p<0.05 were considered to be significant. Table 1 showed characteristics of obese and non-obese groups. Age, sex, and body height were not statistically significant, while body weight and BMI were statistically higher in obese group. Colorectal polyps were found in 57 of 112 obese (50.9 %), whereas only in 124 of 429 non-obese (28.9 %) (p<0.001). Biopsy or polypectomy was performed for all polyps, which were diagnosed as adenomatous polyps by histopathological examination. In consistent with previous studies [3,4,6] we have clearly demonstrated an association between obesity and colorectal adenomas in Japanese adult people in the current study performing total colonoscopy in all subjects. In contrast, an inverse relationship between obesity and colorectal adenomas has been reported in Western countries.[5] However, risk factors for colorectal polyps are not clear. This discrepancy might be due to racial and/or lifestyle differences. Since this is a cross-sectional study at a single University Hospital, prospective multi-centred case-control study is needed to demonstrate a close association between obesity and colorectal polyp in Japanese.

References

(1) Terry PD, Miller AB, Rohan TE. Obesity and colorectal cancer risk in women. Gut 2002;51:191-4.

(2) Murphy TK, Calle EE, Rodriguez C, et al. Body mass index and colon cancer mortality in a large prospective study. Am J Epidemiol 2000;152:847-854.

(3) Bayerdorffer E, Mannes GA, Ochsenkuhn T, et al. Increased risk of 'high-risk' colorectal adenomas in overweight men. Gastroenterology 1993;104:137-144.

(4) Neugut AI, Lee WC, Garbowski GC, et al. Obesity and colorectal adenomatous polyps. J Natl Cancer Inst 1991;83:359-361.

(5) Little J, Logan RF, Hawtin PG, et al. Colorectal adenomas and energy intake, body size and physical activity: a case-control study of subjects participating in the Nottingham faecal occult blood screening programme. Br J Cancer 1993;67:172-176.

(6) Kono S, Handa K, Hayabuchi H, et al. Obesity, weight gain and risk of colon adenomas in Japanese men. Jpn J Cancer Res 1999;90:805-811.

Table 1 Characteristics of subjects