Relationship of serum irisin levels to prevalence and progression of coronary artery calcification: A prospective, population-based study.

BACKGROUND: The mechanisms by which exercise reduces the risk of coronary heart disease remain poorly understood. Irisin, an exercise-induced polypeptide secreted from skeletal muscles, is proposed to potentially mediate beneficial effects of exercise, especially in metabolic regulation and development of atherosclerosis. We examined whether higher serum irisin levels are associated with lower prevalence and progression of coronary atherosclerosis.

METHODS AND RESULTS: We performed a prospective, population-based study of Japanese men aged 40-79 years without known coronary heart disease. We measured baseline serum irisin levels using an enzyme-linked immunosorbent assay and quantified coronary artery calcification (CAC) from serial computed tomography scans. Of 1038 participants (mean age, 63.9 years) at baseline, 670 (64.6%) had prevalent CAC. Of 810 participants at follow-up (median, 5.1 years), 407 (50.3%) experienced CAC progression. In Poisson regression with robust error variance adjusted for age and behavioral factors, serum irisin levels were inversely associated with CAC prevalence (relative risk [RR] of 4th versus 1st quartiles [95% confidence interval], 0.88 [0.78-0.99]; trend P = 0.016) and CAC progression (RR, 0.76 [0.63-0.91]; trend P = 0.002). After further adjustment for cardiometabolic risk factors, the inverse association with CAC prevalence disappeared (RR, 0.95 [0.84-1.08]; trend P = 0.319), but that with CAC progression persisted (RR, 0.77 [0.64-0.93]; trend P = 0.003). These associations were consistent when we applied ordinal logistic regression and across subgroups by cardiometabolic risk factor status.

CONCLUSIONS: Higher serum irisin levels were associated with less burden of coronary atherosclerosis. This association would be mediated through and beyond traditional cardiometabolic pathways.