The influence of smartphone reduction on heart rate variability: a secondary analysis from a randomised controlled trial.

Background: Despite the benefits smartphone technology offers, our phones are available to us almost all of the time and excessive smartphone use may be linked to problematic behaviours and mental illness symptoms. Therefore management of our daily screen time is integral to wellbeing in the digital era. Design: A recent randomised controlled trial (NCT06353451) randomised university students (N=111) to either reduce their daily phone use (intervention) or continue use as normal (control). Using a cross-over design, the control group later received the intervention. The results demonstrated that reducing smartphone use to <2hrs/day improved self-reported mental health, as compared to a control group with no change in screen time. Methods: The aim of this paper was a secondary analysis of daily heart rate variability data (HRV) measured with Fitbit devices to assess physiological changes during the intervention. A total of 45 participants provided baseline, intervention and follow-up HRV data. Mental health variables were measured using standardised questionnaires. Results: A linear multilevel regression indicated HRV significantly declined during the intervention compared to baseline. HRV during the intervention significantly correlated with craving and sleep quality. Conclusions: This may suggest that participants are experiencing a response akin to withdrawal from a behavioural addiction. Importantly, participants reported improved mental wellbeing, suggesting benefits of controlled smartphone use, but our findings provide a deeper insight into the processes underlying reduction in smartphone use and suggest craving and sleep hygiene may be important factors to additionally consider in future studies.