In the mixed model, time after exercise was a significant factor for the decrease in serum YKL-40 overall (P<0.0001), but no difference in YKL-40 decrease over time could be demonstrated between the two groups (P=0.12). There was no difference of the effect of time on YKL-40 between the groups (P=0.76), as illustrated in Fig. 3.
In this study, we investigated the effect of exercise on the inflammatory biomarker serum YKL-40 in patients with CAD versus controls. We found that serum YKL-40 was higher at baseline for the CAD patients compared with the controls, and in both groups serum YKL-40 decreased after exercise with a slightly steeper decrease for the CAD patients than the controls. Time after exercise was a significant factor for decrease in serum YKL-40 overall, but we did not observe a difference in serum YKL-40 decrease over time between the two groups, indicating that exercise has a beneficial effect on the inflammatory level independent of atherosclerotic degree.
In this study, it was interesting that we did not see a difference between CAD patients and controls with respect to YKL-40 decrease after exercise. It has already been established that the formation of fatty streaks and atherosclerosis begins early in life 28,29 and advanced atherosclerotic lesions may already appear in young adulthood 29,30. Our control group had a mean age of 53.5 years and were therefore likely to have developed atherosclerosis despite the fact that they did not have stenosis nor coronary artery calcification on CT angiography. Inflammation plays a central role in atherosclerosis 2, and this could explain why we observed a decrease in both groups and why exercise had a positive effect on inflammation in both CAD patients and controls.
A recent study demonstrated increasing plasma YKL-40 and muscle tissue YKL-40 mRNA values after 1 h of intensive exercise 23. Another recent study showed that marathon running increased the levels of circulating YKL-40 by 56% 31. However, yet another study observed no effect on serum YKL-40 after physical exercise 32. It is possible that a higher intensity and/or a longer duration are necessary for induction of increases in circulating YKL-40 levels in response to exercise. However, none of the mentioned studies considered the changes in YKL-40 after exercise as did the present study.
The authors thank the Department of Cardiology at Hillerød Hospital Copenhagen University Hospital, Denmark where the examinations have taken place. They thank Ulla Kjærulff-Hansen, Dorthe Mogensen, and Marianne Sørensen, Department of Medicine, Herlev Hospital for excellent technical assistance with the serum YKL-40 analysis. Last but not least, they also thank the participants for their willingness to contribute to the research.
There are no conflicts of interest.
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