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About four in 10 cases of cancer can be prevented through lifestyle change, according to a new Canadian study.

The study, published Wednesday in the journal Preventive Medicine, was put together by a team of researchers across Canada in partnership with the Canadian Cancer Society. Their goal was to estimate how many cancer cases in the population were caused by various lifestyle factors and how those causes might change over time.

In 2015, the researchers estimated, nearly 70,000 cancer cases across Canada were likely attributable to things like diet choices, exercise, air pollution and other preventable risk factors.

The researchers think there could be 102,000 preventable cases of cancer in Canada by 2042, given current trends in these risk factors combined with an aging population.

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“Many Canadians are not aware that their lifestyle can have such a dramatic impact on their eventual cancer risk and that Canadians can take action to reduce their personal risk of cancer,” said Dr. Darren Brenner, assistant professor in the departments of oncology and community health sciences at the University of Calgary and a co-author of the study.

Here are the top preventable risk factors for cancer, according to the research:

Smoking

Smoking is responsible for about 72 per cent of lung cancers and 74 per cent of cancers of the larynx, the researchers found. But it’s also responsible for a significant percentage of colorectal, liver, stomach and kidney cancers.

“Tobacco is still by far and away the leading preventable cause of cancer. It accounts for actually almost half of all the preventable cancer cases in our study,” Brenner said. Tweet This

One of the most important things you can do to reduce your cancer risk is to live smoke-free, according to Elizabeth Holmes, policy analyst with the Canadian Cancer Society.

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“Smoking rates are decreasing, but it still remains the number 1 preventable cause of cancer and it really speaks to the importance of continued work in tobacco control measures,” she said.

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Brenner said he isn’t sure how vaping’s growing popularity will affect smoking rates and cancer cases.

“It’s a really important public health question that we don’t have a good grasp of yet,” he said.

Physical inactivity

Physical inactivity, which the researchers defined by setting a maximum daily energy expenditure by weight, is the second-largest preventable risk factor for cancer.

It contributes to lung, colorectal, liver, oral, stomach, kidney, bladder and breast cancers, according to the paper.

Sedentary behaviour — spending a lot of time not moving at all — is a little different but also contributes to cancer risk, Brenner said.

“There is something about being sedentary. There is something about being obese that is associated with an increased risk of cancer but is not necessarily a cause and effect,” said Dr. David Price, a family physician and chair of the department of family medicine at McMaster University.

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Obesity and inactivity don’t directly cause cancer in the same way that tobacco clearly does, he said, but it is associated with a higher risk.

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“I think what this study is saying is that if we continue on the same trend of, as a society being overweight, as a society being less active, we would likely see an increase in the number of cancers,” Price said. Tweet This

The Canadian Cancer Society recommends “move more, sit less” as a good way to cut your cancer risk.

Excess weight

Excess weight contributed to 7,200 new cancer cases in 2015, according to the research. The researchers expect this to nearly triple by 2042 and overtake physical inactivity as the second-most common preventable cause of cancer behind smoking.

If more Canadians had a healthy body weight — defined as a body mass index of at most 25 kg/m2 — about 110,600 cancer cases could be prevented by 2042, the researchers said.

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“We don’t have recent numbers on how aware people are but, in the last 10 years, we saw that only about a third of people were aware of the link between excess weight and cancer risk,” Holmes said. “So, certainly, this is an opportunity to raise that awareness.”

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Diet

Diets low in fruits and vegetables and diets high in processed meats and red meat all contribute to cancer risk, according to the research. They’re associated with lung, liver, colorectal and pancreatic cancers.

That’s why the Canadian Cancer Society recommends “eating well” as a good way to help decrease your cancer risk.

Alcohol is also associated with a large number of cancer cases, including 18 per cent of cancers of the oral cavity and pharynx as well as colorectal, liver, larynx, stomach, pancreatic and breast cancers.

Sun exposure

The sun is associated with skin cancer — which, unfortunately, is the most common kind of cancer.

Practising sun safety by doing things like wearing a hat or long sleeves in the sun and properly using sunscreen could cut your risk of this preventable cancer, according to the Canadian Cancer Society.

Prevention isn’t everything

Cancer isn’t a perfect cause and effect as many cancers aren’t preventable, Holmes said.

“The findings of the study are that about four in 10 cancers can be prevented,” she said. “Which means that about six in 10 cancers cannot be prevented.

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“There are things that we cannot change, like our age, sex, genetics and family history, that influence our cancer risk.” Tweet This

Price said he has patients who tell him they’ve done everything right.

“’I’m a good weight. I exercise. I don’t take much alcohol. I eat healthy. And I got cancer. Like, what gives?’” he said.

“And what I say to patients is: ‘Look, maybe if you hadn’t done all those things, you might have developed cancer five years earlier, or we might not have detected it as early. Or you might respond to the treatment better.’”

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By changing your lifestyle through healthy eating, exercise and quitting smoking, you can still cut your risk of cancer, though, Holmes said.

“What these results are not saying (is) that making changes to risk doesn’t mean that you won’t get cancer,” Brenner said. “But it also means that your chance of getting (the) disease is lower.”