Background: Physical activity has been associated with a reduced risk of coronary heart disease, but the mechanism underlying this association is unclear. Because coronary heart disease is increasingly seen as an inflammatory process, it might be reasonable to hypothesize that physical activity reduces risk of coronary heart disease by reducing or preventing inflammation.

Methods: The study examined the relationship between physical activity and elevated inflammation as indicated by a high C-reactive protein level, white blood cell count, or fibrinogen level. Study subjects were 3638 apparently healthy US men and women 40 years and older who participated in the Third National Health and Nutrition Examination Survey.

Results: More frequent physical activity was independently associated with a lower odds of having an elevated C-reactive protein level. Compared with those engaging in physical activity 0 to 3 times per month, the odds of having an elevated C-reactive protein level was reduced among those engaging in physical activity 4 to 21 times per month (odds ratio, 0.77; 95% confidence interval, 0.58-1.02) and 22 or more times per month (odds ratio, 0.63; 95% confidence interval, 0.43-0.93) (P for trend,.02). Similar associations were seen for white blood cell count and fibrinogen levels.

Conclusions: More frequent physical activity is independently associated with a lower odds of having elevated inflammation levels among apparently healthy US adults 40 years and older, independent of several confounding factors. The results suggest that the association between physical activity and reduced coronary heart disease risk may be mediated by anti-inflammatory effects of regular physical activity.