Effect of body mass index on colorectal cancer

Objective: To evaluate the association between obesity and the risk of colorectal cancer. Methods: 331 patients with rectal cancer and 175 with colon cancer who accepted surgical operation at Beijing Cancer Hospital during 1995 and 2002 were enrolled. Data were collected by reviewing the pathology materials and hospital records. 258 healthy people who accepted health examination at Beijing Cancer Hospital during 2000 and 2002 were also enrolled as control. Data of height, weight and gender at the time of examination were also collected. Obesity was estimated by body mass index (BMI), computed as weight in kilograms divided by height in meters squared (kg/m2). The degree of obesity was compared between the two groups using BMI18.5, 24-27.9 and 28 (kg/m2) as the cut-off points for underweight, overweight and obesity. Associations with obesity were estimated by odds ratios (ORs) and 95% confidence intervals (CIs). All ORs were adjusted for age and sex. Results: Obesity was significantly prevalent in female patients with rectal cancer. All the patients with colon cancer showed lower level of BMI than control subjects. The ORs for rectal cancer rose with increasing BMI in women. Meanwhile, the ORs for colon cancer dropped with increasing BMI in both men and women. Obesity was an independent risk factor for rectal cancer, but not an independent risk factor for colon cancer. Conclusion: Rectal cancer and colon cancer may have different biological behavior. Obese women have relatively high risk for rectal cancer.