Photo courtesy: Flickr user Josiah Mackenzie
There’s new evidence out today that being fit reduces your risk for getting cancer.
The study, released at the American Society of Clinical Oncology’s annual meeting, looked at the link between fitness in middle-aged men and the likelihood of a cancer diagnosis later in life.
Doctors focused on the top three cancers in men: prostate, colorectal and lung. According to the Centers for Disease Control and Prevention, more than 400,000 men were diagnosed with one of these cancers in 2007.
The study tracked 7,000 healthy, 45-year old men. Their fitness was assessed during their regular preventive health exam by putting them on the treadmill. How far — and how well they were able to tolerate increases in the speed and grade of the treadmill — determined how “fit” they were.
Two decades later, when the men were 65, doctors looked at who had developed cancer and compared that to their previous fitness levels. They saw a link — “fit” individuals were less likely to develop cancer, and if they did develop it, they generally had better prognoses.
“That’s what’s really sort of amazing is that there’s really no other population where we have the assessment back in time, when they were in their middle age,” according to Dr. Susan Lakoski, the study’s primary author. “We followed them all the way to past the age of 65 and beyond to track whether or not they’ve developed cancer to see what this relationship was between fitness and cancer risk.”
The study began in 1970 at the Cooper Center Longitudinal Studies in Dallas. The participants were predominantly Caucasian.
Dr. Lakoski focuses on cardiovascular health among cancer patients. She spoke with PBS NewsHour earlier this week.
PBS NewsHour: In a nutshell, what did the study reveal?
Dr. Susan Lakoski, University of Vermont College of Medicine: The study shows that cardiorespiratory fitness predicts cancer risk and prognosis after a cancer diagnosis in men. This is a new finding, because traditionally patients self-report their physical activity. But in our study, we measured it with an objective exercise sonar test.
This is the first study that really addresses the issue of fitness being a prognostic marker of cancer risk in men, and then a marker of prognosis after a cancer diagnosis. We specifically looked at if “fitness,” or the ability to get on a treadmill and go as far as you can, predicted whether or not you’ll develop cancer. And it did predict it. So people who had lower fitness, or went less time on the treadmill, were more at risk for developing cancer later in life.
NewsHour: What’s the difference between physical activity and fitness?
Dr. Susan Lakoski: Physical activity is one part of fitness, and so when you are being physically active and you’re working out, you’re contributing to your overall fitness.
When we ask the participants to get on a treadmill, we’re measuring their cardiorespiratory or cardiopulmonary fitness. That’s the efficiency of oxygen consumption during maximum exercise. Fitness from a clinical standpoint is really, we’re going to see how far you can go on this treadmill, and how well you do — that tells us whether or not you’re going to live longer after a cancer diagnosis, or whether you’ll develop cancer in the first place.
There are lots of different activities that go into what someone’s fitness is — your exercise training, whether it’s running or walking, all are contributing to your fitness. So there’s lots of different physical activities you could do to improve your fitness.
NewsHour: How did you measure their fitness?
Dr. Susan Lakoski: One of the real strengths of this study, because we did it in more than 7,000 men, at baseline, instead of asking them, “How much did you exercise?” We didn’t do that, we actually got them on a treadmill and increased the grade on the treadmill, the speed of the treadmill, over time to see how far they could go. So it was a very accurate way to look at exercise exposure instead of just asking them, “How much do you exercise?”
NewsHour: Is there any way to know what causes this reduced link of cancer from exercising?
Dr. Susan Lakoski: Your fitness is your ability to be efficient at getting oxygen to all of your organs. And we know that being efficient and getting oxygen to all of your organs is very important in modulating different pathways involved in inflammation, hormone levels, immune surveillance, oxidative damage. All of these things play into reducing cancer risk.
We did not assess those pathways in this particular study, but what we did show was that fitness does reduce the risk of cancer.
NewsHour: Have there been other studies looking at, generally, exercise and cancer?
Dr. Susan Lakoski: Yes, there have been some studies done on physical activity and cancer risk. In those studies, there’s been supportive data to show that physical activity reduces risk for breast cancer, colorectal cancer, there’s some controversy on prostate cancer risk.
NewsHour: Explain the controversy.
Dr. Susan Lakoski: It’s very hard to measure someone’s physical activity. I can ask you, how active were you in middle age? What were you doing? How often were you doing it? What intensity were you doing it? You would get a lot of different answers and a lot of different recall bias, because people don’t remember or they might tweak a little what they’re actually doing in terms of physical activity. And because of that, the measure of physical activity is a little bit messy, and we can’t see the signal between physical activity and cancer risk as powerfully because our measure, our questionnaire, is not that great.
So that’s why fitness, where we’re actually measuring someone’s exercise exposure, with a treadmill test is a much more powerful predictor because it’s not based on someone’s recollection of their physical activities. It’s based on how well they do on a treadmill test, which is highly determined by their past physical activity exposure.
NewsHour: Can you tell if it’s the fitness that is reducing their cancer risk, or some other factor like weight, or smoking?
Dr. Susan Lakoski: When we did the study, we adjusted and accounted for other factors. We accounted for smoking, we accounted for body weight, so that it wasn’t just if something’s related to an outcome and we put BMI in the model and that relationship goes away, we can see with confidence that fitness is not really related to the outcome of interest. But when we accounted for those things – or things that might be related – we saw that fitness was equally predictive of outcomes. And so, that’s the best we can do in an epidemiological study.
NewsHour: Bottom line, what would you tell your patients or other patients to do?
Dr. Susan Lakoski: In terms of what patients and clinicians should do, I feel that our focus should be on not only on our standard predictors, but we now know that being fit is very important in reducing risk for chronic illness, specifically for cardiovascular disease and now for men. So the focus should also be fitness, irrespective of your body weight. And that you can get your fitness assessed by seeing your primary care doctor and/or a doctor that specializes in cardio-oncology, which is what I am. So the message is, be fit.
NewsHour: What’s next?
Dr. Susan Lakoski: We need to determine what specific pathways are associated with fitness and cancer risk, and we need to do this study across all different cancers in men and women.
I’m also a very big proponent of bringing exercise tolerance testing to assess fitness in a broader range of populations. We do it very well in the cardiovascular population, but now every cancer patient that comes to see me, I’m putting them on the treadmill and assessing their fitness. Because I know that fitness is an important tool to assess your ability to get through their cancer treatment, and also their prognosis after a cancer diagnosis. And so I think this is going to be a very useful tool as we go forward in the cancer setting, but it’s not really utilized at this point. That’s our goal down the road.
This conversation was lightly edited for clarity. Photo of Dr. Lakoski courtesy of ASCO and the University of Vermont College of Medicine.