Excess weight will become the second leading cause of cancer in Canada in roughly 20 years, behind tobacco, unless a series of targeted actions are taken to reduce the number of people who are overweight and obese.

The finding, revealed in a study funded by the Canadian Cancer Society and published on Wednesday, is part of the first-ever comprehensive snapshot of how rates of 30 different types of cancer will be affected by smoking rates, physical activity, excess weight and other risk factors.

To do the study, researchers looked at cancer incidence data from 2015 and applied information about Canadian smoking rates, sun exposure, physical activity levels and a host of other modifiable lifestyle factors to determine how those rates will change over time.

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Based on that analysis, researchers determined the number of cancer cases caused by excess weight will triple by 2042, rising to more than 21,000 from 7,200 in 2015. The findings were published in the journal Preventive Medicine.

More than 60 per cent of Canadian adults are overweight or obese, according to Statistics Canada. “Overweight” is defined as a body mass index higher than 25, while “obese” is someone with a BMI higher than 30. Right now, excess weight is the third leading preventable cause of cancer behind tobacco and physical inactivity.

While many people are aware of the connection between excess weight and ailments such as heart disease, more work needs to be done so people understand it also raises their cancer risk, said Christine Friedenreich, co-principal investigator of the study.

“It is so complicated,” said Dr. Friedenreich, who is scientific director for the department of cancer epidemiology and prevention research at Alberta Health Services. “It isn’t something we can easily change, but I think raising awareness is the first thing.”

The rising rates of excess weight in Canada are caused by a range of factors, which include everything from access to nutritious, affordable food, physical-activity policies in schools to neighbourhood design. Dr. Friedenreich said solving this complex problem won’t be easy, but that policy-makers can look to past successes in reducing smoking rates, for instance, for inspiration.

She highlighted the fact last week, Health Canada announced that soon all tobacco packages in Canada will have to be sold in brown packages devoid of any brand logos or colours, which is the latest in a long series of steps to help make smoking less appealing and accessible.

Dr. Friedenreich said the study results should send a strong message to policy-makers that they need to adopt specific strategies to combat the problem of excess weight. She added this is one reason why the study is valuable, as publishing this data and spelling out the extent of the problem can help spur action.

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“I think sometimes, for decision-makers, having those numbers right in front may help motivate them to make some changes,” Dr. Friedenreich said.