More variable circadian rhythms in epilepsy: a retrospective cross-sectional study using long-term heart rate recordings from wearable sensors

Background: The circadian rhythm aligns physiology and behaviour with the 24-hour light-dark cycle, and its disruption is linked to neurological disorders such as epilepsy. However, how to best quantify circadian disruption remains unclear, as it can manifest across various properties and timescales. A promising but under-explored approach is to assess the intra-individual variability in circadian rhythms over timescales of weeks to years. This is yet to be studied in epilepsy. Methods: We retrospectively used wearable smartwatch data (Fitbit) from 143 people with epilepsy (PWE) and 31 controls. For each participant, we extracted the circadian oscillation underlying their heart rate time series and analysed the intra-individual variability of three circadian properties: period, acrophase, and amplitude. Findings: We found increased intra-individual variability in period (77 min vs. 62 min, z=3.32, p