Many things that cause cancer are not under our control. These include genetics, family history and early environmental exposures. That’s the bad news.
But the good news is that current research has identified a number of factors in the development of many types of cancer that are under our control. Modify these and we may mitigate risk. There are a few big ones: we can avoid too much sun exposure, quit smoking, eat better and become more physically active. It’s the last one, physical activity, that many people find surprising.
WHAT DOES THE RESEARCH SAY?
Dr. Christine Friedenreich, an epidemiologist in cancer care at Alberta Health Services, is a world expert on the associations between exercise and cancer prevention. She conducted a number of studies looking at large groups of women with breast cancer. She has since expanded her studies to include a wide variety of cancers to try to identify differences between people who went on to develop cancer and those who stayed healthy. In fact, a very large body of research on the relationship between exercise and cancer has accumulated, with hundreds of studies looking at hundreds of thousands of people all around the world.
Recently Dr. Friedenreich reviewed all these papers in the European Journal of Cancer (2010) and concluded that overall, physical activity decreases the risk for cancers by about 25 per cent. That means that one in four cancers could have been prevented by increasing levels of physical activity alone. The types of cancers that have the strongest research support for this association are colon, breast, endometrial (uterine), lung, prostate and possibly ovarian. Other types of cancer have not been studied enough to conclusively say whether physical activity would help or not, but it is likely that this effect translates across most cancer types. The authors estimated that in Europe, if people exercised more, as many as 330,000 new cases of cancer could have been prevented in 2008 alone.
HOW MUCH EXERCISE IS ENOUGH?
The recommendations based on this large body of research say that people should do 30 to 60 minutes of moderate or vigorous activity at least five days a week. Moderate activity includes walking briskly, gardening, cycling or dancing, but can also include household or occupational tasks such as scrubbing, mopping, vacuuming, hammering or lifting and carrying heavy objects such as building materials or even groceries. More vigorous activities include anything that makes you breathe hard, such as running, swimming laps, playing sports such as soccer or hockey, climbing stairs or biking up hills.
HOW DOES PHYSICAL ACTIVITY PREVENT CANCER?
Many studies are underway looking at several possible reasons for this effect. The best understood mechanisms behind exercise’s impact in reducing cancer across groups relate to the beneficial effects of lowering body fat and increasing muscle mass. Less fat on your body results in lower levels of some hormones related to cancers, including estrogens and testosterone. Lower body fat also improves insulin sensitivity and resistance and decreases markers of inflammation. Improved lung function as a result of physical activity may also lower concentrations of cancer-causing materials in the lungs. All of these biomarkers are known to be risk factors for various forms of cancer.
WHEN IS IT TOO LATE?
The good news is it’s never too late. In fact, research shows that the biggest effect of exercise on prevention of breast cancer occurs in women over the age of 50. So whatever you enjoy doing, get out there and do more of it. There are plenty of resources out there that encourage inactive people to incorporate more physical activity. Not only is exercise good for your mental health and physical strength and stamina, we now know it can also help to prevent cancer.
Dr. Linda Carlson (lindacarlson.ca) is the Enbridge Chair in Psychosocial Oncology at the Tom Baker Cancer Centre and a clinical psychologist at the University of Calgary.