LAUSR

An eveningness chronotype is generally associated with reduced sleep continuity and quality, as well as social jetlag. Changes in hormones and menstrual phase similarly impact sleep, although research on the chronobiological effects of these changes are equivocal. This study aimed to examine the role of menstrual cycle in daily self-report and actigraphy-assessed sleep in two consecutive menstrual cycles. Participants (n=51; 43% Caucasian), 18-35 years (23.67±4.68) completed actigraphy and daily sleep diaries over two menstrual cycles (m days=51.29). Four menstrual phases were identified via dates of menstrual bleeding and urinary ovulation testing: perimenstrual (±3 days of bleeding), mid-follicular, periovulatory, and mid-luteal. Relationships between menstrual phase and sleep parameters were estimated using multistep hierarchical linear modeling. Subjective and objective measures yielded the following sleep variables: Total Wake Time (TWTsub and TWTobj), Sleep Efficiency (SEsub and SEobj), and mid-sleep point (MSP). Participants completed the Morning-Eveningness Questionnaire (MEQ) at baseline. Mean cycle length was 28.61 days±2.69. Age was significantly associated with TWTobj (r=-.32, p <.001); SEobj (r=.34, p <.001), and MSP (r=-.42, p <.001) such that older participants had shorter TWT, higher SE, and earlier MSP. TWTobj was 4-7 minutes lower during the mid-follicular (61.54±3.37) and mid-luteal phases (63.11±3.29) compared to the perimenstrual phase (67.54±3.37; p <.001). SEobj was higher in the mid-luteal phase (82.50±0.79) vs. the perimenstrual phase (80.71±0.82, p =.006). Perimenstrual women reported 8-16 minutes longer awake (TWTsub=52.23±5.01, p <.001) and had 1-3% reduction in SEsub (89.70±0.10, p <.001). MEQ negatively predicted TWTobj (p=.004) and SEobj (p=.003), but did not vary across menstrual phase. In morning-type individuals, TST was significantly higher in the periovulatory (b =1.81, p=.01) and mid-luteal phases (b=2.03, p<.001) compared to the perimenstrual phase. With increasing age, women experienced reduced time awake, higher sleep efficiency, and earlier sleep timing. Eveningness predicted greater total wake time and lower sleep efficiency. With menstrual phase considered, disturbed sleep was highest in the perimenstrual phase and women reporting a stronger preference for eveningness reported shorter TST during the perimenstrual phase. These findings highlight the importance of considering the menstrual cycle in the sleep health of menstruating individuals.