NEW YORK (Reuters Health) - Exercise has long been known to cut the risk of heart disease, and now the results of a new study show it may do so, in part, by reducing inflammation inside blood vessels.

Levels of C-reactive protein (CRP), a compound that is used to gauge inflammation in the body, were lower among study participants who reported the most physical activity.

The body releases CRP as part of its response to infection and injury. During infection, blood CRP levels temporarily soar as the immune system jumps into action. More subtly, chronic CRP elevations have been linked to an increased risk of heart disease and type 2 diabetes, and inflammation is believed to play a key role in the hardening and narrowing of arteries that can lead to heart attack and stroke.

"The results of this study showed that physical activity is inversely associated with C-reactive protein concentrations, suggesting that physical activity may mitigate inflammation," Earl S. Ford, from the Centers for Disease Control and Prevention in Atlanta, Georgia, reports in the September issue of Epidemiology.

More research into the mechanism by which exercise affects CRP, as well as studies investigating the intensity, duration and type of activities that influence inflammation, are needed, he adds.

Ford analyzed data on nearly 14,000 adults participating in an ongoing US medical study. He looked at concentrations of CRP in relation to each individual's self-reported exercise habits, and took into account other factors that can influence levels of the protein, including smoking, blood pressure, body mass index (BMI), aspirin use, age and gender.

Ford found that participants' blood concentrations of CRP declined as levels of activity rose. For instance, just 8% of vigorous exercisers had elevated CRP, compared with 13% of moderately active and 21% of sedentary adults.

What's more, exercise was associated with a lower white blood cell count, another marker of inflammation and disease, and with lower levels of the protein fibrinogen. Elevated blood fibrinogen can increase the risk of clotting and stroke.

Levels of physical activity were, on average, lower among older people, smokers and those with high blood pressure and cholesterol. Overweight individuals and those with lower levels of education also reported less activity, while men, white adults and those who consumed the most alcohol, fruit and vegetables tended to exercise more than their peers.

"Research to delineate the exact mechanisms through which physical activity influences the inflammatory process will help improve our understanding of some of the benefits of physical activity," Ford concludes.

SOURCE: Epidemiology 2002;13:561-568.

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