Autonomic function and change in insulin for exercising postmenopausal women

Purpose: Obesity, physical inactivity and altered estrogen metabolism play an integrated role contributing to the disease risk profiles of postmenopausal women. These same risk factors also affect modulation of the autonomic nervous system (ANS). Methods: We examined 332 postmenopausal, overweight, previously sedentary women (mean ± SD; age, 57.6 ± 6.3 years; weight, 84.3 ± 11.9 kg; BMI, 31.7 ± 3.7 kg/m²) participating in a 6-month, moderate intensity, aerobic exercise training intervention to determine the relationship between heart rate variability (HRV) derived autonomic function and fasting insulin. We analyzed quartiles of change in time and frequency domain indices of ANS activity and changes in insulin for between and within group differences using ANCOVA and Tukey post hoc tests adjusted for age, ethnicity, randomization group, change in fitness, and change in weight. Results: We observed at baseline that insulin was positively correlated with body anthropometry (body weight, r² = 0.34; BMI, r² = 0.39; waist circumference, r² = 0.29; all, P < 0.001), and inversely associated with rMSSD (r² = -0.12) and SDNN (r² = -0.18; all, P < 0.01). After the intervention, changes in rMSSD (r² = -0.21, P < 0.002) and SDNN r² -0.19, P < 0.0001) were inversely correlated to insulin change. Further ANCOVA analysis revealed that rMSSD and SDNN were both significant (P < 0.0001); however, only rMSSD exhibited a step-wise pattern of improvement when quartiles of rMSSD were compared to corresponding insulin reductions: Q1 (referent group, 8.41 ± 3.2 uIU/ml), Q2 (-3.30 ± -3.2 uIU/ml), Q3 (-5.66 ± -3.2 uIU/ml; P < 0.02), and Q4 (-9.60 ± -3.2 uIU/ml; P < 0.006). Conclusion: Our study shows that changes in autonomic function are associated with changes in insulin and that exercise training may influence this relationship in postmenopausal women.