WASHINGTON -- Physically fit people are less likely to die of cancer, including cancers related to smoking, even if they smoke, a study finds.
But other studies indicate the benefit may come only with vigorous exercise; less-intense activities, such as brisk walks, won't be enough.
''Fitness may provide protection against cancer mortality,'' said the study in the May issue of the journal Medicine and Science in Sports and Exercise.
The researchers followed 25,892 men ages 30 to 87 who took treadmill tests to determine the most exercise they could do. The men were followed for an average of 10 years. In this time, there were 133 deaths from cancers related to smoking and 202 deaths from other cancers.
The most-fit men had a 55 percent lower risk of all-cause cancer death than did low-fit men, and moderately fit men had a 38 percent lower risk, said researchers Chong Do Lee of West Texas A&M University and Steven N. Blair of the Cooper Institute of Dallas.
To be moderately fit, a person would have to run 20 to 40 minutes, three to five times a week. To be most fit, a person would have to be at the recreationally competitive level.
The most-fit men had a 46 percent lower risk, and moderately fit men had a 34 percent lower risk of cancers unrelated to smoking. These diseases include cancers of the colon and prostate, and leukemia, which affects white blood cells.
The most-fit men had a 66 percent lower risk and the moderately fit men a 43 percent lower risk of cancers related to smoking, such as cancers of the lung and mouth. If the least-fit smokers had become fit, they would have reduced their death risk by 13 percent, a statistical analysis in the study concluded.
The most-fit men were least likely to smoke, but almost 10 percent of them did, as did 20 percent of moderately fit men and 33 percent of sedentary men. The most-fit and moderately fit smokers were still less likely to die than were the sedentary smokers, Lee said. ''If you are a high-fit smoker, then you should have a lower risk,'' Lee said.
Just the same, Lee and other experts say exercise is no substitute for giving up smoking. The study found that nonsmokers who were the most physically fit had the lowest risk of dying of cancer.
The researchers theorized that the heavy breathing that comes with vigorous activity clears the lungs of some cancer-causing chemicals associated with smoking. And fitness may help the body in other ways, such as improving defensive systems that may keep tumors from forming, they said.
''This is a seminal study,'' said Scott Leischow, chief of the tobacco control research branch of the National Cancer Institute. He was not involved in the study.
The study should encourage smokers who can't -- or won't -- quit to be at least good exercisers, he said.
Smokers should check with a doctor before starting an exercise program, because smoking can cause otherwise hidden problems such as heart disease, which the stress of exercise may trigger, Leischow said.
The study could not rule out the possibility that cancer death may simply have come after the average of 10 years that the researchers examined. And the researchers did not tally new diagnoses, so they could not tell if exercise prevented cancer or simply helped the exercisers survive it.
It's possible that the physically fit men simply were better able to benefit from cancer treatment, which itself can be arduous, said Dr. George Selby of the University of Oklahoma, who was not connected with the study.
Another possibility is that the fit men also were more careful about their own health and saw doctors more often, so their cancers were diagnosed earlier when the chance of successful treatment was greater, Selby said.
Although Selby counsels people to exercise for other health benefits, he said he could not yet tell them that exercise would reduce their risk of dying of cancer.
Selby also underscored the importance of giving up smoking, and the sooner, the better. Light smokers who quit while young can reduce their cancer risk by up to 90 percent, but heavier smokers who quit later in life may get as little as a 20 percent risk reduction, he said.
And even the low-fit men in the study were able to put out a lot of effort. In the tests, all the subjects hit at least 85 percent of their maximum aerobic ability -- equivalent to the effort in jogging. And the tests continued for at least 25 minutes.
One separate study found no reduction in cancer risk from less-intense activity. Researchers at Britain's Royal Free and University College Medical School followed 7,588 men ages 40-59 for an average of almost 19 years.
The British scientists found a reduced risk of all cancer only with moderately vigorous or vigorous activity; there was no benefit with less work.
''Sporting activity was essential to achieve significant benefit,'' said the report, published in November 2001 in the British Journal of Cancer. And the more strenuous the activity, the greater was the benefit, the study found.
On the Net:
Medicine and Science in Sports and Exercise: http://www.ms-se.com
National Cancer Institute: http://www.nci.nih.gov/cancer--information/pdq/
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