Highlights
- Excess body weight (overweight and obesity) is an established risk factor for several cancers.
- In Ontario, incidence rates for most cancer types strongly linked to excess body weight as a known risk factor have risen in parallel to the rise in obesity rates observed between 1983 and 2012.
- The number of cancers attributed to excess body weight is expected to rise if the proportion of the population that is overweight and obese continues to increase.
In Ontario, incidence rates, or rates of new cases, for several cancers associated with excess body weight (overweight and obesity) have been rising in parallel with obesity rates. Excess body weight is responsible for a substantial burden of cancer in the province. In 2010, it was estimated that over 2,600 new cancer cases (equivalent to roughly 4% of all new cancers) diagnosed in Ontario could be attributed to overweight and obesity.[1]
Of the cancers strongly associated with excess body weight, incidence rates increased significantly for cancer of the esophagus (adenocarcinoma), uterus, kidney, pancreas and liver between 1983 and 2012. For adenocarcinoma of the esophagus, incidence rates began increasing in 1986, at an annual rate of 3.5%, and continued through 2012. During that same time period, liver cancer rates rose steadily and significantly at a rate of 3.8% annually. Kidney cancer incidence increased by 4.1% per year from 1983 to 1990, stabilized during the early 1990s and began increasing again at an annual rate of 1.7% from 1995 to 2012. Although incidence rates for cancer of the uterus (including endometrium) and cancer of the pancreas were initially declining, they have increased in recent years.
In contrast, colorectal cancer incidence has been declining since 1983, and rates for post-menopausal breast cancer increased during the 1980s but stabilized during the 1990s onwards. Both of these cancers, however, are associated with several risk factors in addition to excess body weight, and have well-established screening tests that may influence their incidence rates. Rising rates of overweight and obesity and a parallel rise in the incidence of several associated cancers have also been observed in other jurisdictions, including the United States.[2]
The proportion of the Ontario population that is considered overweight or obese has risen rapidly in recent decades. In 2012, over 18% of adults age 18 years or older were considered obese, based on self-reported height and weight, compared with roughly 4% in 1985. With obesity rates projected to continue rising in future years,[3] it is anticipated that the number of cancer cases related to excess body weight will continue to grow unless effective prevention efforts are implemented.