Infradian rhythms of human heart rate reveal distinct multiday cycle periods in healthy adults

Abstract

BACKGROUND: Chronobiology research has historically focused on circadian rhythms; however, longer infradian rhythms are prevalent in human physiology and may have important implications for health and wellbeing. Previous studies have identified widespread infradian rhythms across human physiology, often in the context of hormonal regulation and disease. Despite growing evidence of their ubiquity, the mechanisms, significance, and clinical relevance of these rhythms remain poorly understood, largely reflecting a lack of longitudinal datasets and robust detection methods. The emergence of new wearable technologies enables rich, continuous data capture within individuals, allowing physiological rhythms to be studied at scale. METHODS: This retrospective, observational cohort study analysed young adults (n = 623), with up to four years of wearable and questionnaire data collected through the University of Notre Dame's (USA) NetHealth project. Participants who recorded at least three months of continuous (>80% data completeness) heart rate data were included and significant infradian rhythms were identified using wavelet analysis. Unsupervised non-negative matrix factorisation was performed to cluster similar wavelet power spectrum distributions. Individuals' heart rate rhythms were compared to known environmental cycles (day-of-week, lunar, seasonal) and considering demographics and social networks. A second, smaller cohort (n = 70) with heart rate and menstrual timing was included to analyse the interplay of hormonal regulation on monthly cycles. Multinomial logistic regression and the Kruskal-Wallis test were applied to quantify the effects of environmental, behavioural and demographic factors on heart rate rhythms. FINDINGS: Significant infradian rhythms of heart rate were detected in 70% (369/525) of the cohort and 36% (187/525) had two or more rhythms. Annual, biannual and 10-week rhythms were the most common. Within the 4-45-day band, individuals clustered into three multiday chronotypes based on dominant periodicities in their wavelet power spectra: weekly (∼7 days), monthly (∼25-35 days), and multi-month (>35 days). Heart rate rhythms were influenced by environmental cycles (day-of-week and seasonality) and were synchronised to the menstrual cycle in most menstruating females, although monthly rhythms were also observed in males and menopausal women. INTERPRETATION: The prevalence of infradian, or multiday heart rate rhythms in healthy young people motivates further scientific investigation to understand the mechanisms of these rhythms and their potential association with autonomic function, and risk of disease or disease-specific symptoms. FUNDING: This study was funded by an Australian Research Council Grant (DP240102899). This study also received funding from the Australian National Health and Medical Research Council Medical Research Future Fund (MRFF 2039966).