Circulating irisin in healthy, young individuals: Day-night rhythm, effects of food intake and exercise, and associations with gender, physical activity, diet, and body composition

Abstract

Patients and Interventions: One hundred twenty-two healthy, young individuals were subjected to anthropometric and body composition measurements, and their eating and exercise behavior profiles were assessed with validated questionnaires. Subgroups were subjected to day-night rhythm, standardized meal ingestion, and 30-minute aerobic exercise studies. Main Outcome Measures: Circulating irisin levels were measured. Results: Irisin levels were lower in males than females (P=.02) after adjustment for lean body mass, which was its major determinant. Irisin levels followed a day-night rhythm (P < .001). Irisin levels were not affected by intake of a standardized meal and were not associated with caloric intake or diet quality. Conclusions: In healthy, young individuals, circulating irisin displays a day-night rhythm, is correlated with lean body mass, and increases acutely after exercise. Setting:Thestudywasconducted at the Hellenic Military School of Medicine (Thessaloniki, Greece). Context: The myokine irisin may increase energy expenditure and affect metabolism. Copyright Objective: The objective of the study was to elucidate predictors of irisin and study whether circulating irisin may have day-night rhythm in humans. Design: This was an observational, cross-sectional study with an additional 24-hour prospective observational arm (day-night rhythm substudy) and two prospective interventional arms (mixed meal substudy and exercise substudy).