Background: Obesity has been linked with increased risk for cancers of the colon, kidney, breast, endometrium and gallbladder. For other cancer sites, the relationship with obesity is less well quantified, and the effect of weight change on cancer risk is unclear.
Methods: We examined the health records of 362,552 Swedish men who underwent at least one physical examination from 1971 to 1992, and were followed until death or the end of 1999. Incident cancer cases were identified by linkage to the Swedish cancer registry. Poisson regression models were used to estimate relative risks of cancer for both body-mass index (BMI) at baseline exam and, in a subgroup of 107,815 men, change in BMI after six years of follow-up, adjusting for age and smoking status.
Results: Compared to men of normal weight, obese men had a significantly increased risk of all cancers combined (RR = 1.1; 95% CI = 1.0-1.2). The risks were most pronounced for esophageal adenocarcinoma (RR = 2.7; 95% CI = 1.3-5.6), renal cell carcinoma (RR = 1.8; 95% CI = 1.4-2.4), malignant melanoma (RR = 1.4; 95% CI = 1.1-1.7), and cancers of the colon (RR = 1.7; 95% CI = 1.5-2.0), rectum (RR = 1.4; 95% CI = 1.1-1.7), and liver (RR = 3.6; 95% CI = 2.6-5.0). Risk of esophageal squamous cell carcinoma was elevated for underweight men whose BMI was less than 18.5 (RR = 3.1; 95% CI = 1.1-8.3). An excess risk for cancers of the pancreas and connective tissue was observed only among nonsmokers. Compared to men whose weight remained stable, men with more than a 15% increase in BMI after six years of follow-up had an elevated risk of pancreas and renal cell cancers.
Conclusions: Obesity and weight gain increase the risk for several forms of cancer in men, and underscore the need for further study into carcinogenic mechanisms and preventive interventions.