Exercise, even a couple of hours a week, appears to reduce the risk of breast cancer, colon and lung cancer, the researchers, who looked at 1.4 million adults.
"Those are three of the four major types of cancer affecting Americans today," said Marilie Gammon, a professor of epidemiology at the Gillings School of Public Health at the University of North Carolina at Chapel Hill.
And the fans to be fit should be encouraged: cancer risk seems to decline as they increase the hours of physical activity without a cap apparent, said study author Steven Moore, researcher at the National Cancer Institute US.
"A more activity, more profit," Moore said. "As people became more, their risk continued to decline."
But it should be noted that the study only found an association between exercise and a lower risk of cancer, it did not prove a causal relationship.
In the study, regular exercise ended linking with a reduced risk of 13 cancers in all, the researchers said. The others were leukemia, myeloma and cancers of the esophagus, liver, kidney, stomach, endometrial, rectum, bladder, and head and neck.
Current federal guidelines on exercise (150 minutes of moderate-intensity activity per week, or 75 minutes of vigorous activity) are directed to heart health, but also work well for cancer prevention, Moore said.
The moderate-intensity exercise involves activities such as brisk walking or tennis, while vigorous intensity exercise involves activities that put your heart beat, such as running or swimming laps, according to the Office of Disease Prevention and Promotion of Health. UU.
In this study, Moore and his colleagues focused on leisure time physical activity carried out work or household chores. "It is usually performed voluntary physical activity to improve health," he said.
About half of American adults do not meet the minimum exercise federal recommendation, the study authors said in the backup information.
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Previous research has linked exercise with a lower risk of breast and colon cancer, but no study had tried to observe the effect of physical activity on several different types of cancer, Moore said.
The researchers pooled data from 12 studies of EE. UU. and Europeans to create a database of 1.4 million adults 19 to 98 years old. Then they examined whether physical activity reported by participants posed a difference in risk of 26 cancers.
The exercise was associated with a lower risk than half of cancers including by investigators, and this reduction remained significant in almost all, even after taking into account risk factors such as obesity and smoking history.
In general, a higher level of physical activity was associated with a 7 percent risk lower total cancer, the researchers reported.
The range of risk reduction ranged from 42 percent for esophageal cancer up to 10 percent for breast cancer, the study authors said. As to colon cancer and lung cancer, the risk was reduced by 16 and 26 percent, respectively, they suggested the findings.
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"This suggests that physical activity may have a role in population cancer prevention efforts," Moore said.
The findings appear in the online edition May 16 issue of the journal JAMA Internal Medicine .
Nobody knows for sure why exercise appears to help prevent cancer, they commented Moore and Gammon, but there are some prominent theories.
Physical activity reduces the levels of hormones such as estrogen, which have been linked to various cancers, and helps control insulin levels and insulin-like growth factor, said Moore.
People who exercise also tend to have lower levels of inflammation, Moore said. Your cells also appear to suffer less oxidative stress, and be able to repair damage that could cause cancer, said Gammon, co-author of an editorial published with the study DNA.
Gammon said what pleased him most was the 42 percent reduction in the risk of esophageal cancer.
"It's pretty amazing, because it is a very lethal tumor," he said. "I think the average survival is 11 to 12 months after diagnosis."
Other highly lethal cancers that appear to be less common with exercise include liver, stomach, kidney, and head and neck, Gammon said.
"Having a strategy to help reduce the risk of these cancers is very good, because once you have been diagnosed prospects are not optimal," he said.
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