Sleep Quality Is Associated With Nighttime Heart Rate Variability In Young Adults

Abstract

Heart rate variability (HRV) reflects autonomic nervous system function, and low nighttime HRV is linked to reduced parasympathetic control. Optimal parasympathetic function is important for the induction and maintenance of sleep, overall wellbeing, and is inversely associated with chronic disease. In young adults, 60% of whom report poor sleep quality, disrupted parasympathetic function may reflect suboptimal health and lifestyle behaviors. While there is an established relationship between physical activity (PA), stress, and nighttime HRV, the associations between HRV and other lifestyle-related factors such as sleep quality and social jet lag (SJL) in young adult populations are yet to be determined. PURPOSE: The purpose of this study was to determine the relationship between nighttime HRV and sleep characteristics in young adults. METHODS: Healthy young adults (n=33, 18.6 ± 0.7 years, 69.6% female) wore a chest-strap heart rate monitor for 24 hours and a triaxial accelerometer on the non-dominant wrist for 7 days during free-living PA and sleep. Average sleep duration and SJL were determined from objective sleep data, with SJL calculated as the difference in hours between the midpoint of sleep on weeknights (school) and weekend (free) nights. The Pittsburgh Sleep Quality Index (PSQI) and Perceived Stress Scale were used as subjective measures of sleep quality and stress. Nighttime HRV outcomes were calculated using R-R intervals between the hours of 1:00 AM - 5:00 AM. Linear regression assessed multivariate relationships among sleep duration, quality, SJL, and HRV while controlling for moderate-to-vigorous PA and perceived stress. RESULTS: Independent of average sleep duration and SJL, perceived sleep quality was associated with the HRV outcomes low frequency (LF; B= -10.62 ± 4.85, 95% CI: -20.56, -.67) and high frequency power (HF; B= 10.55 ± 4.84, 95% CI: .61, 20.49). Following control for PA and stress, these relationships remained significant and the association between SJL and LF/HF ratio approached significance (B= -.33 ± .18, 95% CI: -.69, .04). CONCLUSIONS: Our findings suggest that both LF and HF HRV components are related to sleep quality in young adults, highlighting a potential relationship between sleep quality and nighttime autonomic nervous system function.