LAUSR

College students often experience irregular sleep timing, short sleep duration, and weight gain. Using data from a large, prospective study on sleep in first-year college students, we examined whether students’ sleep regularity index (SRI; Phillips et al., 2017) was associated with body mass index (BMI) and BMI change (∆BMI) during the first nine weeks of their college semester. Analyses included data from 583 students (mean age = 18.7± 0.5 years; 59% Female; 48% non-White) who had their height and weight assessed at the start of classes (T1) and end (T2) of nine weeks. ∆BMI was calculated as the difference between T2 and T1, with a positive value indicating an increase in BMI. Throughout the semester, participants completed on-line daily sleep diaries that included bedtime, wake-time, sleep onset latency, and wake after sleep onset for the previous major sleep episode and daytime naps. Based on this data, total sleep time (TST) was calculated as time spent asleep between bedtime and wake-time, and SRI was calculated by comparing participants’ sleep/wake states across adjacent 24-hour periods. Average SRI reflects participants’ sleep regularity (0 (random) to 100 (perfect regularity)) across the study. Data were analyzed with hierarchical linear regressions that controlled for sex and average TST. Average SRI was 74.1±8.7 (range 25.7–91.6). Average BMI at T1 was 22.0±3.5; 6% of participants were underweight (BMI less than 18.5), 6% overweight (≥25 and <30) and 3% obese (≥30). Greater BMI at T1 was correlated with less ∆BMI by T2 (r=-.16, p<.001). On average, participants gained 1.8±2.4kg (range: -7.2–11.4); 6% of participants lost ≥2kg, 39% gained 2-5kg, 8% gained more than 5kg. Average TST was not significantly correlated with BMI or ∆BMI. Lower SRI was associated with greater BMI at T1 (B= -.06 [95% CI: -.09– -.02], p=.001) but less ∆BMI (B= .01 [.002–.018], p=.018). We found that lower sleep-wake regularity associated with greater baseline BMI but less BMI increase during the initial transition to college. Given that the majority of our participants were normal weight young adults, our findings may indicate that sleep regularity associates with healthy growth in this population. R01MH079179, T32MH019927(P.W.)