Body Position Affects The Relationship Between Heart Rate Variability And Metabolic Health In Young Adults

Abstract

Heart rate variability (HRV), the time-difference between heartbeats, is a convenient and inexpensive marker of autonomic function. Though previous studies have demonstrated associations between HRV and metabolic health, these findings have primarily come from single day laboratory measures, with little consideration for body position or lability in day-to-day HRV. PURPOSE: To examine relationships between self-recorded, multi-day, supine and standing HRV measures with indicators of metabolic health in young healthy adults. METHODS: Twenty-one men (24.4 ± 4.9 yrs) and 20 women (21.4 ± 2.7 yrs) recorded ultra-short (i.e., 60-s), post-waking HRV measures in supine and standing positions for seven days via a Bluetooth heart rate monitor and smartphone application. Following the HRV measurement period, participants reported to the laboratory in a fasted state during morning hours. Total body fat percentage (BF%) was evaluated via dual-energy x-ray absorptiometry and fasting blood glucose (FBG) and total cholesterol (TC) were assessed in fingerstick samples using a point of care device. Associations between 7-day average supine and standing natural logarithm of the root mean square of successive R-R interval differences (lnRMSSDavg), and their coefficients of variation (lnRMSSDcv), with BF%, FBG, and TC were assessed. RESULTS: Supine and standing lnRMSSDavg were 4.4 ± 0.4 and 3.5 ± 0.5 ms in men, and 4.1 ± 0.6 and 3.1 ± 0.5 ms in women, respectively. Supine and standing lnRMSSDcv were 8.1 ± 3.4 and 10.6 ± 5.4 % in men, and 9.8 ± 5.2 and 13.0 ± 4.4 % in women, respectively. FBG and TC were 86.8 ± 7.0 and 174.8 ± 49.7 mg/dl in men (20.9 ± 7.4% body fat), and 84.1 ± 9.7 and 148.2 ± 21.8 mg/dl in women (34.1 ± 7.2% body fat), respectively. Total BF% was associated (P < 0.05) with supine lnRMSSDavg in men (r = -0.47) and women (r = -0.50), as well as lnRMSSDcv in supine (r = 0.50) and standing (r = 0.45) positions in women. TC was associated with supine lnRMSSDavg in men only (r = -0.54; P = 0.01). CONCLUSION: Supine lnRMSSDavg appears to be most strongly related to BF% in young healthy men and women. Associations between supine and standing lnRMSSDcv and BF% that were only observed in women, and supine lnRMSSDavg and TC that were only observed in men, provide evidence in support of gender differences in relationships between HRV and metabolic health.