Associations between body composition and autonomic cardiorespiratory modulation in young adults.

This study investigated the associations between body composition and autonomic cardiac regulation, indexed by heart rate variability (HRV), in clinically healthy young adults, and additionally explored complementary breathing rate variability (BRV) and pulse-respiratory quotient (PRQ) indices. Ninety university students aged 18-23 years (35 men, 55 women) were evaluated. Linear and nonlinear HRV and BRV indices were derived from 5-min R-R and breath-to-breath and PRQ time series. Body mass index (BMI) and bioelectrical impedance-based measures were obtained, including fat mass percentage (%FM), muscle mass, and visceral fat indices. HRV, BRV, PRQ, and composition indices were analyzed, and sex-stratified correlations between body composition and autonomic indices were examined. Men showed greater respiratory variability and lower breathing rate than women. In men, BMI, %FM, and visceral fat indices correlated negatively with parasympathetic modulation and the complexity of cardiac and PRQ series, and positively with sympathetic modulation. In multivariable regression models adjusted for age, breathing rate, and physical activity (assessed with the IPAQ-short form and expressed as total METs/week), higher %FM was independently associated with lower vagally mediated HRV indices in men, but not in women. Higher adiposity (higher BMI, %FM, and visceral fat indices), particularly in young men, was associated with reduced vagal HRV and diminished cardiorespiratory complexity.