Abstract 035: Chronic Mild Sleep Restriction Leads To Increased Sedentary Time And Reductions In Physical Activity
Authors: Zuraikat Faris M , Scaccia Samantha , Diaz Keith M , Cochran Justin , RoyChoudhury Arindam , St-Onge Marie-Pierre 
Published: May 2021

Background:
Sleeping less than 7 h per night is a risk factor for positive energy balance and weight gain. While the effect of short sleep on energy intake has been extensively studied, its influence on physical activity (PA), a key determinant of energy expenditure, is not well characterized. To date, no study has evaluated sedentary and PA patterns in response to chronic mild short sleep, which is experienced by up to one-third of US adults.

Hypothesis:
Sedentary behavior will be higher and PA (light intensity [LIPA] and moderate-vigorous intensity [MVPA]) will be lower during 6 wk of mild sleep restriction (SR) relative to maintenance of adequate sleep (AS).

Methods:
Data are presented from 76 participants (age: 34.2±12.4 y; BMI: 25.6±3.4 kg/m
2
; n=55 women) from two randomized crossover trials with identical sleep interventions. Men and women with adequate habitual sleep duration ≥7 h/ night underwent two 6-wk sleep conditions, AS and SR, separated by a 6-wk washout period. During AS, participants were instructed to maintain average nightly bed and wake times determined from 2 wk screening with wrist-actigraphy and sleep logs. In SR, total sleep time was curtailed by 1.5 h per night by delaying bedtimes. Nightly sleep diaries and 24-h wrist actigraphy confirmed adherence to the protocol, which was verified weekly. Daily wrist actigraphy data were used to determine time spent in sedentary behavior and PA. Linear mixed models were used to test whether sleep condition (SR vs AS) influenced sedentary behavior or PA, adjusting for time in bed.

Results:
Across the full sample, sedentary time was significantly greater in SR than in AS (39.8±13.6 min/d, P<0.01). Similar results were observed in analyses stratified by sex; compared to AS, in SR, sedentary time was 53.0±16.5 min/d higher in women (P=0.001) with a trend towards significance in men (20.3±11.3, P=0.07). Although a slight increase in LIPA over 6 wk was observed in SR relative to AS in the full sample (2.9±0.8 min/d, P<0.001) and in men (3.7±1.2 min/d, P<0.01), overall, time spent in LIPA across weeks was significantly lower in SR relative to AS. This main effect of SR on LIPA was observed in the full sample (SR vs AS: -44.6±3.3 min/d, P<0.0001) and separately in women (SR vs AS: -38.2±10.5 min/d, P<0.001) and men (SR vs AS: -9.4±4.6 min/d, P=0.04). In men only, the slope of change in MVPA over 6 wk differed slightly in SR vs AS (2.6±1.1, P=0.02). However, across weeks, time in MVPA was significantly lower in SR compared to HS (-12.4±4.2 min/d, P=0.003).

Conclusions:
We provide some of the first evidence of an adverse impact of chronic short sleep on PA patterns in men and women. Greater sedentary time and lower PA levels can promote positive energy balance and may underlie associations of short sleep with risk for cardiometabolic diseases. Results further highlight the importance of achieving adequate sleep to promote cardiovascular health.