(Photo: Peter Mooney/Flickr)

A recent report suggested—somewhat dubiously—that running either at high speeds or over long distances could increase the risk of death compared to a more moderate regimen. That may be true, but even if the hypothesis checks out overall, it doesn't apply to non-Hodgkin lymphoma: A new study indicates that vigorous exercise is associated with as much as a 30 percent decrease in the lifetime risk of lymphoma.

Medical researchers have shown that exercise reduces the risk of some, though not necessarily all, cancers. According to a 2010 study, there's "convincing or probable evidence for a beneficial effect of physical activity on the risk of colon, breast and endometrial cancers." (The evidence is weaker for ovarian, lung, and prostate cancer, and is generally absent for other cancers.)

Meanwhile, there've been few studies on the influence of exercise on non-Hodgkin lymphoma (NHL), a relatively common cancer that begins in immune system cells in the lymph nodes, spleen, and bone marrow, among other organs. Only a subset of that research has looked at how exercise intensity might moderate the risk of developing lymphoma.

Getting a decent amount of vigorous exercise—more than about an hour of fast walking a week, for example—was associated with about a 30 percent drop in the odds of coming down with NHL.

Hoping to get some answers, Terry Boyle and colleagues at the University of British Columbia and the British Columbia Cancer Agency looked to data on 749 British Columbians diagnosed with NHL and another 818 healthy residents who'd been matched on the basis of age, sex, and place of residence. In addition, all 1,567 participants answered a series of questions about risk factors for NHL, including their physical activity outside of work.

Surveying participants' exercise habits and measuring metabolic equivalents to compare different kinds of activity, the researchers found no link between the frequency of NHL and individuals' total amount of exercise per week. In other words, adding up every activity from sitting at the computer to intense workouts, exercise had essentially no impact on the likelihood of getting non-Hodgkin lymphoma.

But a different result emerged when focusing in on more vigorous exercise, such as hiking at a fast clip or recreational sports game. Getting a decent amount of vigorous exercise—more than about an hour of fast walking a week, for example—was associated with about a 30 percent drop in the odds of coming down with NHL sometime over the course of one's lifetime, compared with those who got very little vigorous exercise.

Still, the researchers point out their study is one of just three to examine exercise intensity and NHL, and across those three, the results are not entirely consistent. One report found results similar to Boyle's, while the other concluded that women who exercised more vigorously might be at an increased risk of NHL. The new study's design also makes it impossible to say why vigorous exercise is associated with lymphoma risk. As is often the case in careful studies, the researchers write that "more research ... is warranted."

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