Although the inverse relationship between fitness levels and circulating C-reactive protein (CRP) levels is well recognized, the relationship of changes in fitness over time and changes in CRP levels is not well established. To address this issue, Nakajima et al. determined the effect of changes in fitness levels over a 1-year period on CRP levels in 482 healthy middle-aged men who did not receive any particular intervention. Fitness levels were measured using running velocity over a 5 km course. Although CRP concentrations were associated with fitness levels at baseline (r=-0.28, p<0.001), the annual changes in fitness were not associated with proportional decreases in CRP levels. When men were separated based on tertiles of changes in fitness levels, men in the middle tertile had the largest decrease in CRP levels compared to men in either the top or bottom tertiles. Men who had the greatest improvement in their fitness had modest decreases in body mass index and waist circumference. Although changes in fitness were not associated with proportional decreases in CRP levels, further lifestyle intervention studies, rather than observational studies, are required to measure the effect of exercise training or improved fitness levels on inflammatory markers.
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