A prospective study of obesity and cancer risk (Sweden)

Objective: We evaluated the relation between obesity and the risks for various forms of cancer. Methods: In a population-based cohort of 28,129 hospital patients (8165 men, 19,964 women) with any discharge diagnosis of obesity (9557 only diagnosis, 5266 primary, 13,306 secondary) during 1965-1993, cancer incidence was ascertained through 1993 by record linkage to the nationwide Swedish Cancer Registry. Cancer risk was estimated using the standardized incidence ratio (SIR, with 95% confidence interval), which is the ratio of the observed number of cancers to that expected. Results: Overall, a 33% excess incidence of cancer was seen in obese persons, 25% in men and 37% in women. Significant risk elevations were observed for cancers of the small intestine (SIR = 2.8; 95% CI 1.6-4.5), colon (1.3; 1.1-1.5), gallbladder (1.6; 1.1-2.3), pancreas (1.5; 1.1-1.9), larynx (2.1; 1.1-3.5), renal parenchyma (2.3; 1.8-2.8), bladder (1.2; 1.0-1.6), cervix uteri (1.4; 1.1-1.9), endometrium (2.9; 2.5-3.4), ovary (1.2; 1.1-1.5), brain (1.5; 1.2-1.9), and connective tissue (1.9; 1.1-3.0), and for lymphomas (1.4; 1.0-1.7), with higher risk observed for Hodgkin's disease only in men (3.3; 1.4-6.5) and for non-Hodgkin's lymphoma only in women (1.6; 1.2-2.1). The association of obesity with risk of breast, prostate and pancreas cancers was modified by age. Conclusions: Obesity is associated with more forms of cancer than previously reported.