Cancers attributable to excess body weight in Canada in 2010

Excess body weight (body mass index [BMI] ≥ 25.00 kg/m2) is an established risk factor for diabetes, hypertension and cardiovascular disease, but its relationship to cancer is lesser-known. This study used population attributable fractions (PAFs) to estimate the cancer burden attributable to excess body weight in Canadian adults (aged 25+ years) in 2010.

We estimated PAFs using relative risk (RR) estimates from the World Cancer Research Fund International Continuous Update Project, BMI-based estimates of overweight (25.00 kg/m2-29.99 kg/m2) and obesity (30.00+ kg/m2) from the 2000-2001 Canadian Community Health Survey, and cancer case counts from the Canadian Cancer Registry. PAFs were based on BMI corrected for the bias in self-reported height and weight.

In Canada in 2010, an estimated 9645 cancer cases were attributable to excess body weight, representing 5.7% of all cancer cases (males 4.9%, females 6.5%). When limiting the analysis to types of cancer associated with high BMI, the PAF increased to 14.9% (males 17.5%, females 13.3%). Types of cancer with the highest PAFs were esophageal adenocarcinoma (42.2%), kidney (25.4%), gastric cardia (20.7%), liver (20.5%), colon (20.5%) and gallbladder (20.2%) for males, and esophageal adenocarcinoma (36.1%), uterus (35.2%), gallbladder (23.7%) and kidney (23.0%) for females. Types of cancer with the greatest number of attributable cases were colon (1445), kidney (780) and advanced prostate (515) for males, and uterus (1825), postmenopausal breast (1765) and colon (675) for females. Irrespective of sex or type of cancer, PAFs were highest in the Prairies (except Alberta) and the Atlantic region and lowest in British Columbia and Quebec.

The cancer burden attributable to excess body weight is substantial and will continue to rise in the near future because of the rising prevalence of overweight and obesity in Canada.