Obesity is an important cause of type 2 diabetes mellitus, hypertension, and dyslipidaemia. The adverse metabolic effects of excess body fat accelerate the development of atheroma and increase the risk of coronary heart disease, stroke, and early death. The association between adiposity and cancer, however, is less well known. In this week's BMJ, Reeves and colleagues report a large prospective cohort study from the United Kingdom—the million women study—which assesses the association between body mass index (BMI) and cancer incidence and mortality.1

In 2002, the International Agency for Research on Cancer (IARC) convened an expert panel—which would draw on epidemiological, clinical, and experimental data—to evaluate the link between weight and cancer.2 It concluded that some colon cancers, postmenopausal breast cancers, endometrial cancers, kidney cancers, and adenocarcinomas of the oesophagus could be prevented by avoiding weight gain. Since …