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THE QUESTION Physical fitness not only helps the heart but also is considered a good way to prevent a range of chronic diseases. Might cancer be among them?

THIS STUDY analyzed data on 13,949 men, 65 and older, who were free of cancer at the start of the study. In about the next six years, 1,310 were diagnosed with prostate cancer, 200 with lung cancer and 181 with colorectal cancer. When they were middle-aged (49 years old, on average), all of the men had participated in cardiorespiratory fitness testing.

Men considered highly fit at midlife, based on those tests, were 55 percent less likely to have developed lung cancer and 44 percent less likely to have developed colorectal cancer later in life than were those who had been the least fit. No link was found between fitness level at middle age and occurrence of prostate cancer after age 65. However, for men who did develop lung, colorectal or prostate cancer later in life, having been highly fit at middle age corresponded to a 32 percent reduced risk for dying from their cancer and a 68 percent risk reduction for death from cardiovascular disease after their cancer diagnosis.

WHO MAY BE AFFECTED? Men. Prostate, lung and colorectal cancer are the three most common cancers among men; they are also the leading causes of men’s death from cancer. Roughly half of all men in the United States will develop some type of cancer in their lifetime.

CAVEATS Nearly all men in the study were white; whether the findings would apply to other races, or to women, remains unclear. Data on fitness came from only midlife testing and did not account for any changes in fitness level in subsequent years. The study did not include data or suggestions on specific exercises or fitness regimens.

FIND THIS STUDY March 26 online issue of JAMA Oncology (oncology.jamanetwork.com/journal.aspx; click “Online First”).

LEARN MORE ABOUT cancer at www.cancer.org. Learn about the benefits of physical activity for adults at www.cdc.gov/physicalactivity.

The research described in Quick Study comes from credible, peer-reviewed journals. Nonetheless, conclusive evidence about a treatment's effectiveness is rarely found in a single study. Anyone considering changing or beginning treatment of any kind should consult with a physician.