0354 Early to Bed and Early to Rise? A Comparison of Actigraphy-derived Sleep and Circadian Timing Across Chronotypes

Abstract Introduction Evening chronotype is associated with increased risk for depression and suicide-related outcomes. This may be due to circadian-sleep misalignment, as previous studies have found chronotype-related differences in the relative timing between circadian phase (i.e., dim light melatonin; DLMO) and sleep. However, such differences may be attributable to variation in intrinsic circadian period length across chronotypes, rather than reflect actual circadian misalignment among those with an evening chronotype. The present study sought to compare predicted circadian and sleep timing across chronotypes using a light-based mathematical model of the human circadian pacemaker that controlled for intrinsic period length. Methods This was a secondary analysis of the Multi-Ethnic Study of Atherosclerosis (MESA) Sleep and the Hispanic Health Study / Study of Latinos (HCHS/SOL) Sueño datasets. Scores on the Reduced Morningness-Eveningness Questionnaire were grouped into “morning,” “intermediate,” and “evening” chronotypes. Sleep timing was determined by actigraphy and DLMO was predicted (pDLMO) from light and sleep/wake states using the extended Kronauer model. Circadian-sleep alignment was calculated as the timing between pDLMO and either sleep onset or offset (i.e., phase angles). Multivariate analyses of covariance (MANCOVAs) were used to evaluate the associations between chronotype and the timing/alignment of circadian and sleep variables, with post-hoc comparisons conducted using non-parametric bootstrapping. Results MANCOVAs identified chronotype differences in sleep onset, pDLMO, and pDLMO-sleep onset phase angles in both datasets. Chronotype was associated with pDLMO-sleep offset phase angles in MESA Sleep only. pDLMO and sleep onset were ~1-2 hours later for participants with an evening chronotype (p .001 for all). In MESA Sleep, participants with an evening chronotype had a pDLMO-sleep onset phase angle that was ~30 minutes (95% CI: 13.5, 46.9; p = .002) shorter than those with a morning chronotype; in HCHS/SOL Sueño, it was ~17 minutes (95% CI: 3.6, 29.1; p = .033) shorter. Conclusion Assuming equal intrinsic periods, participants with an evening chronotype had a light exposure profile that predicted sleep onset at an earlier circadian phase than those with a morning or intermediate chronotype. These findings provide further evidence that an evening chronotype may be associated with chronic circadian-sleep misalignment. Support (if any) None