The Association between Obesity and Cancer Risk: A Meta-Analysis of Observational Studies from 1985 to 2011

Background. Cancer and cardiovascular diseases are the leading causes of mortality and morbidity worldwide. The purpose of this meta-analysis is to synthesize the evidence evaluating the association between obesity and 13 cancers shown previously to be significantly associated with obesity. Methods. Relevant papers from a previously conducted review were included in this paper. In addition, database searches of Medline and Embase identified studies published from the date of the search conducted for the previous review (January, 2007) until May, 2011. The reference lists of relevant studies and systematic reviews were screened to identify additional studies. Relevance assessment, quality assessment, and data extraction for each study were conducted by two reviewers independently. Meta-analysis was performed for men and women separately using DerSimonian and Laird’s random effects model. Results. A total of 98 studies conducted in 18 countries from 1985 to 2011 were included. Data extraction was completed on the 57 studies judged to be of strong and moderate methodological quality. Results illustrated that obese men were at higher risk for developing colon (Risk Ratio (RR), 1.57), renal (1.57), gallbladder (1.47), pancreatic (1.36), and malignant melanoma cancers (1.26). Obese women were at higher risk for esophageal adenocarcinoma (2.04), endometrial (1.85), gallbladder (1.82), renal (1.72), pancreatic (1.34), leukemia (1.32), postmenopausal breast (1.25), and colon cancers (1.19). Conclusions. The results of this meta-analysis illustrate a significant, positive, and, for some cancers, strong association between obesity and cancer incidence. Given that approximately 23% of Canadians are obese, a significant proportion of cancer in Canada could be avoided if obesity was eliminated or significantly reduced. 1. Introduction Chronic diseases are the leading cause of mortality and morbidity and contribute significantly to the overall health expenditures from both a societal perspective as well as an individual one [1]. Common chronic diseases include heart disease, stroke, cancer, emphysema, diabetes, and osteoporosis. Furthermore, cancer and cardiovascular diseases are the leading causes of mortality and morbidity worldwide [2], with cancer expected to result in 75,000 deaths per year in Canada [3] and 571,950 in the US [4]. While the leading risk factor for cancer continues to be tobacco use, evidence shows that obese men and women have a greater likelihood of developing and dying from cancer than those who are not [2, 5–7]. Obesity is defined as a Body