Scientists are pinpointing just how much behaviour can influence the incidence of cancer, which is the No. 1 cause of mortality in Canada, responsible for 86,700 deaths in 2023. In fact, experts unequivocally say almost a third of 239,100 new cancers diagnosed that year were preventable.

Lowering risk is also a matter of statistics and probabilities. “Everybody understands that if you drive a little drunk, you might not get into an accident, but it’s certain you’re more likely to,” says Dr. Michael Pollak, professor of medicine and oncology at McGill University and director of the oncology department’s cancer prevention division. “You have to look at cancer risk and cancer prevention that way. If you smoke, or drink three glasses of wine a day, it’s like driving a car with unreliable brakes. You might get away with it, but you’re definitely living with increased risk.” The trouble is, “even if you do everything perfectly, it does not guarantee that you will not get cancer.”

Pollak says even one glass of wine a week will equal a detectable increased risk of breast cancer, albeit a tiny one. His advice: a couple of glasses of wine a week, and no more. “The amount of risk from that is much less than, say, smoking a pack of cigarettes a day for lung cancer, but if you take a million women and each of them increases their chance of developing breast cancer by 15 per cent, then you’ve got thousands of preventable breast cancers.”

Some things, however, can’t be helped: family history, genetics, living in polluted environments and unknown exposure to carcinogens. Maybe you were a committed sunbather or smoker as a young person, before the dangers were fully understood. Maybe you’re lucky enough to be cancer-free at 65, but just be aware about half of all cases are diagnosed after that.

The good news is even if you made less-than-healthy choices in the past, there’s still hope, because eliminating these risk factors can help.

Eat Smart: According to the Canadian Partnership Against Cancer (CPAC), a federally funded non-profit, diet accounts for about 10 per cent of all cancer cases. Consuming more fibre and less processed and red meat, sugar, and saturated and trans fats decreases the risk of developing endometrial, breast, colorectal, lung, pancreatic, prostate, esophageal and stomach cancers.

Watch the Scale: Obesity is a risk factor for endometrial, uterine, liver and postmenopausal breast cancer and Pollak says it can also hinder the effectiveness of cancer treatment. “If you’re 20 pounds overweight, your cancer risk may be 10 per cent higher,” he adds. “It’s not as bad as smoking, but the prevalence of obesity is so large that if you have five million people in Canada who are significantly overweight and each of them has a 10 per cent increase in cancer risk, that’s hundreds of thousands of cases.”

Get treated: Medical conditions like hepatitis, HIV and GERD, or acid reflux, can increase cancer risk. According to the American Centers for Disease Control, about two-thirds of the population is infected with H. pylori, a stomach bacterium that can cause problems like chronic indigestion, but is easily treated with antibiotics. Untreated, it can lead to stomach ulcers and stomach cancer. Similarly, untreated GERD can increase the risk of esophageal cancer. 

A version of this article appeared in the April/May 2025 issue with the headline ‘An Ounce of Prevention’, p. 54.