SHUTTERSTOCK

Exercise is a key weapon in the fight against cancer, researchers say.

Altering lifestyle can help prevent disease

Lose weight to cut your risk of breast cancer? Exercise more?

Yes, say disease experts: Being active and reducing body fat are among the most effective ways women can protect themselves.

When "environment" and "cancer" are mentioned, we tend to think of the pesticides, plastics and thousands of other chemicals introduced in the past 60 years.

These man-made substances, now embedded in every human body, are implicated in many health problems, including damage to the nervous and reproductive systems. Some studies link them to certain types of cancer and they may well be responsible for many more.

It's believed general exposure to these chemicals is connected to just 5 to 10 per cent of cancer deaths, says Dr. John Spinelli, senior scientist at the B.C. Cancer Research Centre in Vancouver.

Still, he and others say it's prudent to reduce chemical contamination as much as possible. Many exposures are beyond control, but others are open to direct action – the most obvious being eliminating tobacco use.

"In fact, things we can control may be the most important," says Gail Eyssen, associate director of the Dalla Lana School of Public Health at the University of Toronto. "For a number of cancer sites ... the major causes are not environmental chemicals, but the way we eat," as well as how much alcohol we drink and how active we are.

Research suggests cancer of the breast and womb, as well as several other malignancies, are more likely when women are overweight and less likely when they're active.

"One-third of cancers could be prevented through better diet and regular exercise," says the London-based World Cancer Research Fund, which has published a report compiling the results of thousands of cancer-cause studies.

The research is about risks, not certainties. Some things are more closely correlated with cancer; others less. The best evidence in the Research Fund's independent analysis is merely "convincing."

But the conclusions are compelling enough for Eyssen and others to recommend women change their personal "environment."

The risk of breast cancer increases with women's body fat and height. It's also higher for those who grew faster as children.

As for chemicals, there might be a link between breast cancer and age of exposure. A recent study found that among a group of California women exposed to DDT half a century ago, those exposed before age 14 were five times more likely to eventually be diagnosed with breast cancer.

As with all aspects of cancer, Spinelli says, more research is needed.

That's happening. Hundreds of studies are underway, including one that will analyze blood samples from 400,000 Canadians, then seek links between chemicals in the blood and what happens to those people over the next 20 years.