History of COVID-19 and Circadian Light Hygiene in Young Adults

Background — The COVID-19 pandemic disrupted sleep and circadian rhythms, but the specific effects of prior infection on the body’s response to light for circadian regulation remain unclear. This study builds on previous research examining COVID-19 status and susceptibility to daylight by investigating seasonal variations in light hygiene and sleep parameters among young adults. Methods — We enrolled 187 medical students (mean age, 19.03±1.63 years; 132 females) from Tyumen, Russia. Participants wore ActTrust2 actigraphy devices with RGB light sensors for 1 week in spring (April-May; n=95) or autumn (October-November; n=92). We quantified circadian light hygiene using parametric and nonparametric measures, along with the normalized circadian amplitude of blue light exposure (NA BLE). Participants were grouped by COVID-19 infection history. We analyzed data with multiple linear regression and two-way ANOVA. Results — COVID-19-negative individuals had significantly higher daytime light exposure than COVID-19-positive individuals. Season and NA BLE were significant predictors of sleep parameters, with spring associated with shorter sleep duration and earlier bedtime compared with autumn. Higher NA BLE correlated with longer sleep duration, earlier bedtime, and greater relative amplitude of activity. Two-way ANOVA showed significant interactions between COVID-19 status and NA BLE for bedtime (p=0.021) and total sleep duration (p=0.019). These results indicate that prior COVID-19 infection modulates the association between light hygiene and sleep timing. Conclusions — Prior COVID-19 infection is linked to reduced daylight exposure and alters circadian sensitivity to light, affecting sleep timing and quality in young adults. These findings support considering COVID-19 history when developing light-based circadian interventions.