Association between environmental and headphone noise and heart rate variability: observations from Apple Hearing Study cohort

BACKGROUND: Environmental noise is linked to adverse cardiovascular effects. However, few studies have examined people's heart rate variability (HRV) changes related to noise sources, despite the elevated cardiovascular risk associated with reduced HRV. OBJECTIVES: We investigated HRV changes following short- and long-term lagged environmental and headphone sound exposure, assessed using the standard deviation of normal-to-normal intervals (SDNN). We also examined effect modification by individual characteristics. METHODS: Eligible participants were a subset of consented adults from the Apple Hearing Study, a nationwide prospective cohort. Analyses were constructed into four analytical cohorts defined by sound source (environmental vs. headphone) and exposure window (short-term: 20 min vs. long-term: 160 min). In each cohort, twenty participants were randomly sampled from each unique age-sex-ethnicity group. Smartwatches and smartphones measured sound levels and 1-min SDNN estimates. Distributed lag non-linear hierarchical Bayesian models estimated lag-specific and overall changes in first-stage analyses, adjusting for time of day and physical activity, with random effects to capture individual-specific variation. Second-stage linear regression models summarized the average change by age, sex, BMI, stress, self-rated hearing ability, and tinnitus. RESULTS: The stratified sampling ranged from 980 to 1180 participants across analyses. An overall SDNN reduction of 6.8% (short-term) to 16.0% (long-term) was observed following a 10-decibel increase in environmental noise exposure, and 7.1% (short-term) to 7.4% (long-term) for headphone sound. Lag-specific prediction showed brief initial SDNN increases followed by sustained reductions. Greater SDNN reductions were seen in older adults, individuals with tinnitus, or individuals who reported excellent hearing (for environmental noise) or those who reported poor hearing (for headphone sound). SIGNIFICANCE: Findings suggested noise-HRV relationships differed by exposure window, noise source, and individual characteristics, highlighting the importance of stratified risk assessment, especially in the elderly and individuals with hearing loss. However, generalizability may be limited by cohort characteristics and reliance on consumer-grade wearables. IMPACT: The physiological stress associated with noise exposure can persist from minutes to hours, as reflected by decreasing heart rate variability associated with elevated noise exposure levels. Given the association between chronically low heart rate variability and higher risk of cardiovascular diseases, noise source-specific risk assessments and noise control efforts are warranted for future studies on the non-auditory health effects, particularly for vulnerable populations.