Age- and sex-related differences in heart rate variability are present despite the suitable level of accelerometer-based physical activity

Background: Previous studies have described the age- and sex-related differences in heart rate variability (HRV) regardless of the level of physical activity in daily life (PADL). However, such studies were based in the assessment of PADL by means of questionnaires, which present important recall limitations. The influence of age and sex on HRV, free of the confound effect of accelerometer-based PADL, was not sufficiently investigated, especially in asymptomatic adults. We tested the hypothesis that a suitable level of accelerometer-based PADL might solve or at least minimize the influence of age and sex on cardiac autonomic balance assessed by HRV.

Purpose: We aimed to evaluate age- and sex-related differences in HRV adjusted by the accelerometer-based PADL in asymptomatic adults.

Methods: A total of 488 asymptomatic adults older than 18 years (200 men), selected from the Epidemiological Study on Human Movement and Hypokinetic Diseases (EPIMOV Study) were enrolled. Five-minute HRV measurements in supine position were undertaken with Polar chest belts. The data were analyzed in time and frequency domains. The participants wore an Actigraph GT3X+ accelerometer for 7 days. Physical inactivity was defined as less than 150 min/wk of moderate to vigorous physical activity. Other cardiovascular risk factors were recorded such as hypertension, diabetes, obesity, and smoking. The self-reported uses of continue medication was also recorded. Two-way ANOVA and multivariate regression analysis adjusted by PADL and the main cofounders were developed to assess the age- and sex-related differences in HRV. The correlation between HRV indices and PADL variables were evaluated using Spearman correlation coefficients.

Results: In the time domain, age was important for standard deviation of the normal RR intervals (SDNN), the root mean square of successive differences (RMSSD) and the percentage of consecutive normal RR intervals >50 ms (pNN50), and sex was not selected as significant for such indices. In the frequency domain, age and sex were significantly associated with low frequency (LF) and high frequency (HF) bands of HRV. In general, women presented better frequency domain indices (p < 0.05). After adjusting for quantity and intensity of the accelerometer-based PADL and main cofounders, age and sex remained significantly associated with the same HRV indices. We observed significant interactions between age and sex related to SDNN, RMSSD, pNN50 and LF. Physical inactivity was significantly associated with SDNN, RMSSD, pNN50, HF and LF. Interesting, the correlation between indices of HRV became moderate but significant only with the time spent in vigorous accelerometer-based PADL, with a range r = 0.19 to r = 0.30. After adjusted models, diabetes was associated with LF/HF ratio and obesity was associated with LF.

Conclusions: We may conclude that autonomic control of heart is negatively affected by aging. Our results suggest a positive influence of sex (female) on vagal tone. These age- and sex-related differences are present despite a suitable level of accelerometer-based PADL.