Chronic Exercise Training and Circulating Irisin in Adults: A Meta-Analysis

Area of Science:

• Endocrinology and Metabolism
• Exercise Physiology

Background:

• Irisin, a newly discovered hormone, is a potential therapeutic target for obesity and type 2 diabetes.
• Previous studies on irisin's association with chronic exercise training in adults have yielded inconsistent results.

Purpose of the Study:

• To meta-analyze randomized controlled trials (RCTs) and non-randomized studies (NRSs) separately.
• To evaluate the effects of chronic exercise training on circulating irisin levels in adults.

Main Methods:

• A systematic literature search was conducted in PubMed, Web of Science, and Cochrane Library databases (January 2012–September 2014).
• Included studies assessed chronic exercise training (≥8 weeks) effects on circulating irisin in adults (mean age ≥18 years).
• Pooled effect sizes (Cohen's d) were calculated using a random-effects model, with subgroup analyses for exercise modes.

Main Results:

• Twelve studies (3 RCTs, 9 NRSs) were included.
• In RCTs (n=173), chronic exercise training significantly decreased circulating irisin (d = -0.46).
• Resistance exercise showed a significant decrease (d = -0.41), while endurance exercise showed a trend (d = -0.64).
• In NRSs (n=113), the effect of exercise on irisin was trivial and non-significant (d = -0.04).

Conclusions:

• Chronic exercise training significantly reduces circulating irisin levels based on RCT evidence.
• Evidence from NRSs is inconclusive regarding the impact of exercise on irisin.
• Future well-designed RCTs are needed, incorporating dietary intake and body composition/insulin sensitivity measures.