Age and sex affect circadian patterns of cardiac autonomic function

The cardiovascular system exhibits circadian rhythmicity, responding to central and peripheral clocks. Sexual dimorphism and aging independently influence circadian rhythms and cardiac electrical activity, which the autonomic nervous system regulates. However, the extent to which sex and aging affect autonomic dynamics remains unclear. This study investigates their role in circadian cardiac autonomic activity in healthy subjects. Data from 51 males and 51 females with 24-hour Holter recordings were analyzed. Circadian patterns of Heart Rate Variability parameters, indicators of autonomic function, were assessed using fast Fourier transformation with 5-minute Blackman-Harris windows on artifact-free recordings. Fractal, multifractal, visual, and information methods were applied to evaluate parasympathetic and sympathetic influences. We calculated the means and standard deviation for all numeric variables. We found temporal fluctuations across the time domain and frequency parameters. Six of the eight nonlinear HRV parameters significantly fluctuated. Among the 17 fluctuating parameters analyzed, nine circadian indicators (MESOR, amplitude, and acrophase) showed significant differences between sexes, with women exhibiting higher vagal oscillatory activity. Aging diminished fluctuations across all parameters and was associated with chronodisruption of cardiac autonomic markers. These findings highlight neurohumoral differences as key modulators of cardiac autonomic dynamics. The interaction effect of sex and age impacts the circadian rhythmicity of cardiac electric activity, as reflected by the HRV analysis. Our results have implications for personalized diagnostics, treatment timing, risk prediction, and biomarkers, highlighting the need for age-and sex-specific approaches in precision medicine and chronomedicine.