One activity is associated with a reduced risk of 13 cancers
A team of researchers wanted to know whether people who said they were physically active in their free time saw lower risks of 26 types of cancer than their couch potato peers. For half the cancers studied, they did.
The results were published on May 16 in JAMA Internal Medicine.
While there have been plenty of studies tying higher rates of cancer to obesity, study co-author Steve Moore of the National Cancer Institute was curious when he realized no one had really looked at cancer and activity on a large scale.
For more common cancers, like breast cancer, the link between exercise and lower risk was already pretty solid. "In some ways it just kind of confirmed the earlier small studies," said Marilie Gammon, a cancer researcher at the University of North Carolina, Chapel Hill, who wrote a commentary on the new study for JAMA.
But what gave the new study its heft was that scientists took the original data from a dozen previous studies and analyzed it from scratch. That meant the researchers could look at much rarer cancers as well, like esophageal adenocarcinoma, which affects about 5 in 100,000 people in the US.
Gundula Behrens, an epidemiologist at the University of Regensburg in Germany who has done research on exercise and the rates of different cancers but wasn't affiliated with this study, said she was pleased to see that the large number of patients involved meant researchers could separate out overweight people and people who have smoked - both of whom have a heightened risk of cancer.
The researchers were able to see that regular exercisers had a reduced risk of cancer even if they were also overweight or a smoker. That suggests that the link between physical activity and cancer is not just a red herring: Exercise itself seems tied to cancer risk, not just other healthy behaviors that might be associated with it.
Of the cancers the researchers studied, only two - prostate cancer and melanoma - were more common in people who reported more physical activity in their free time.
They think the first may be a coincidence: People who are more likely to exercise regularly are also more likely to schedule regular doctor's visits and get screened, which may mean they're more likely to get a prostate cancer diagnosis. The uptick in melanoma, meanwhile, is likely from people exercising outdoors without wearing sunscreen.
The details are still a little hazy - the study can't identify a minimum amount of exercise to aim for, a specific type of activity that may be more effective than others, or whether exercise needs to be a lifelong habit or can begin later in life. And because the study relied on how much people said they exercised, there's a chance their answers were shaped by how much they wish they had exercised as well as how much they actually did.
But if you need a little extra motivation for your next workout, reminding yourself that exercise is linked to a lower risk of cancer should give you a boost. Just don't forget the sunscreen.