Can exercise prevent cancer?

To say David Smith is the picture of health would be an understatement. The former schoolteacher in Caledon East, an hour northwest of Toronto, is lean and strong, with muscular definition that people half his age can’t help noticing with envy. Smith works out for 90 minutes at least five times each week. Two years ago, at the age of 64, he took up competitive bodybuilding, and he’s been winning in the ultra-masters category of the “natural” (no steroids or other muscle-enhancing substances) circuit in Canada ever since.

Only a circular scar, a mark “about the size of a coffee-cup,” on his clean-shaven head offers any hint of a health problem. Nine years ago, a biopsy of a small spot on his head showed melanoma. Six months later, the skin cancer had grown larger and more serious. Smith underwent surgery and bouts of drug therapy.

Cancer-free since those treatments, Smith is happy to say that his lifelong commitment to exercise played a big part in his recovery. “The doctors said the only reason I survived this bout of cancer was because of all the bodybuilding I’d been doing,” he says.

However, although they’re often regarded one and the same principle, the body’s ability to withstand and reap full benefits from the oftentimes invasive treatments associated with cancer therapy is quite different from the body’s ability to battle invading viruses, unwelcome bacteria or mutant cells. And to say that physical exercise can help fight disease is one statement proof-obsessed scientists have difficulty making – at least, without qualifications.

Kerry Courneya, a researcher at the University of Alberta in Edmonton, set out to study the effects of exercise in improving the quality of life for cancer patients. He hypothesized that exercise could soften the brutal side effects from the treatments that usually follow diagnoses. The topic quickly changed. “People started raising questions like, ‘What are the implications of exercise for things like tumour growth and immune function and recurrence?’ and so on,” says Courneya. Given present research, the professor of kinesiology (the study of human movement) is careful about drawing conclusions about the relationship between exercise and the body’s ability to fight this dreaded disease. “We haven’t got to those outcomes yet so we don’t know,” he says. Not surprising given that cancer is a group of more than 100 diseases, many of which don’t react the same to given stimuli.

Still, the latest studies offer generally good news, says Courneya. “In terms of preventing cancer, the evidence is quite clear that exercise does reduce the risk of breast cancer and colon cancer; and there may be some other cancers as well where exercise will reduce the risk.” Importantly, the bulk of research on disease prevention has focused on one aspect of fitness, according to Courneya. “The studies that have shown a link between exercise and mortality have typically looked at lifelong exercise, exercise over long periods of time.”

Never too late to start
The question, then, is: if long-term physical fitness is key to preventing disease, is it too late to start an exercise program late in life or after being diagnosed with cancer or some other serious illness? Quite the opposite, say the experts. There are good reasons to start an exercise program at any time – in some cases, even when disease is already present.

A report by the American College of Sports Medicine (ACSM) outlines a Dutch study that tested the effects of exercise on immune response in older people. Researchers based their inquiry on the findings of previous studies, which showed that immune responses decline with age, possibly as a result of decreased physical activity and poor nutrition. A group of 112 people with a median age of 79 and described as “frail inactive elderly” was divided into three sub-groups: one was asked to perform 45-minutes of supervised low-level exercises (consisting primarily of warm up, cool down and mobility exercises) twice a week; the second group of subjects was provided with fruit and dairy products enriched with the vitamins usually found to be lacking among people of this age; the third group served as control.

Next page: Statistically significant benefits

After 17 weeks, the exercise program had a small but “statistically significant” beneficial effect, an effect seen in the response of immune cells, according to the ACSM report. By comparison, the nutrition group showed improvement in blood vitamins, mineral concentrations and enzyme activity but no measurable change in immune response.

A yet-unpublished study by Courneya’s group showed results similar to the findings for the Dutch researchers’ active group. “There was an effect on cell function from exercise,” says Courneya. But once again, his optimism about these results is tempered. “We’re not sure of the clinical relevance of that: will it reduce infections in the future or be related to recurrence?” Still, even if it is too soon to say for certain, these results are encouraging to people whose immune function has been depressed by age or who are otherwise sick or frail.

“If you’re talking on the post-diagnosis side and you’re looking at recurrence of the disease, the initial hypothesis is that the factors that influence risk in the first place may be in play,” says Courneya. In other words, while certain modifiable behaviours, such as low levels of physical fitness, are linked to the development of certain cancers, the good news is these same habits – once changed for the positive – also seem to play a part in fighting the same disease. “This gives us reason to believe breast cancer survivors and colorectal cancer survivors may, in fact, reduce their risk of recurrence if they exercise.”

More to the puzzle
If physical conditioning were the only key to immunity, argues Daria Love, a naturopathic doctor in Toronto, fit people wouldn’t get sick in the first place. Indeed, fitness enthusiast David Smith’s battle with cancer is proof of the less-than-perfect correlation between health and fitness. “In terms of disease fighting, when you’ve got the [symptoms of illness], you already have a system that’s showing signs of not only being under siege but losing the battle,” says Love.

Beyond prevention, naturopathic medicine – of which physical exercise is a part – acknowledges that there is sometimes the need to fight disease with antibiotics, radiation or other forms of conventional treatment. “We recognize that, for certain times and for certain people, it is appropriate to direct care most acutely to deal with ‘the invader,’” says Love, who has been practising naturopathic medicine since 1981. The focus here remains the same as in less dire situations: using whatever treatments and therapeutics necessary to support and build the body’s energies, reserves and immunity.

“The advantage of exercise is that [it] stimulates the metabolism, improves oxygenation,” says Love. Like cancer researcher Kerry Courneya, Love believes good health is built and maintained by optimizing the body’s natural processes – including immune response – and exercise is just part of this model. “Good immunity is a factor of a generally healthy body, and there are many components that figure into what makes one healthy. If you’re optimizing how the body is functioning, then the immune system is going to benefit. Exercise is part of the whole wellness concept,” says Love.

The experience of cancer survivor and bodybuilder David Smith bears out this holistic concept of health. “I know there are people who have much more serious problems than I do. But all I can do is control my own lifestyle,” says Smith. “I guess it’s just a healthy lifestyle – good diet, lots of rest and lots of exercise.”

Next page: Quality of life is key – as are timing and balance

And even if experts can’t yet quantify the effects of physical activity on immune function, the measurable improvement in overall physical and mental health is just as important. “People over 50 are concerned about quality of life. They’re very concerned about functional well-being, activities of daily living, so chronic disease is only part of the equation and part of the motivation for exercising,” says cancer researcher Courneya.

But timing and balance are key
Such improvements in quality of life aside, it’s tempting to embrace the idea that we can create our own immunity. If it’s true, then we could simply resolve to live well and fend off disease. Though the whole issue of the impact of the environment on the development of cancer isn’t fully understood, it’s generally accepted that strains on our system from environmental factors – carcinogens in air, water and food, personal stress and poor diet – play a role in immune deficiency. Indeed, Courneya points out that despite much attention to genetic predisposition when it comes to disease, heredity plays a relatively smaller role in cancer than many people believe. “Most experts believe that two-thirds of cancers are due to behavioral-lifestyle types of factors – what we eat, what we drink, exercise levels, obesity and so on. In that sense, behaviors are going to be premium.”

On the other hand, we all know or have heard of people who have fallen seriously ill regardless of healthful living, good habits, even seemingly good genes. In this regard, Love is quick to stress that for some people who are very ill or dealing with suppressed immunity for whatever reason, an exercise program may not help and may even hurt. “Exercise is important as part of a comprehensive program, but timing is too. If a person is exhausted by exercise, there’s no benefit,” says Love. Timing is crucial because if the body is already stressed– whether by battling disease or dealing with some other malfunction – exertion in the form of exercise could end up doing more harm than good.

“In some cases, there has to be more restoration put in place before you can get the person to that point [of benefiting from exercise],” she says. The research seems to bear out her convictions: over-training, or too much exercise, even for athletes who are extremely fit, can depress immune function and increase the probability of illness.

Perhaps more important for those of us fortunate enough to be relatively disease-free, these findings support the notion that we don’t have to be super-athletes. Says Love, “The difference between a bit of exercise and tons [of exercise] is not that big. But the difference between the person who does zero exercise to the person who does some … the health benefits are actually considerable.”