Abstract MP19: Impact of Change in Bedtime Variability on Body Composition: Secondary Findings From the Go Red for Women Strategically Focused Research Network

Abstract

Variability in daily sleep duration and unstable bedtimes are emerging sleep-related factors that have been linked to metabolic syndrome. For example, in longitudinal studies, the odds of developing metabolic syndrome over 6.3 y median follow-up are 1.36 for every 1 h increase in sleep onset variability (standard deviation of bedtimes measured over 7 nights of actigraphy) in fully adjusted models. However, whether reducing bedtime variability improves markers of disease risk has not been tested. Here, we assessed whether body composition was impacted by changes in bedtime variability over a 6-wk period during which women were instructed to maintain healthy, habitual sleep patterns. This was a single arm of a randomized trial originally designed to test the impact of sleep restriction on cardiometabolic risk factors. Women, aged 20 y and older and with body mass index 20-33 kg/m 2 were recruited. All women were required to have adequate sleep duration of 7-9 h/night, determined over 2 wk using wrist-worn actigraphy. Upon randomization, women were given bed and wake time prescriptions aligned with their average screening bed and wake times in order to ensure maintenance of adequate sleep duration over the 6 wk study phase. The alternate phase required women to delay their bedtimes to achieve sleep restriction. Only data from the adequate sleep phase were used for the present analyses. Bedtime variability and body composition data were available for 37 women (age 34.9±12.4 y, BMI 24.7±2.9 kg/m 2 , screening sleep duration 7.58±0.49 h/night). Body composition was measured at baseline (0 wk) and endpoint (6 wk) using magnetic resonance imaging. Bedtime and sleep data were collected weekly using wrist actigraphy. Change in bedtime variability was calculated as the difference in the standard deviation of bedtimes measured during the 2-wk screening period and the 6-wk study phase. Sleep duration did not differ between screening and the average of 6 wk of the sleep phase (-4.8±24.7min, P=0.24). Average percent change in bedtime SD was 24.4±25.2% in those who increased their bedtime variability and -39.9±23.5% in those who reduced their bedtime variability. Results showed that, compared to women who increased or did not change (n=8) bedtime variability, women who reduced their bedtime variability (n=29) during the intervention had significant reductions in total (reduced: -0.52±0.98 vs increase/no change: 0.63±0.41 L, P<0.001) and subcutaneous adipose tissue (reduced: -0.48±0.86 vs increase/no change: 0.56±0.31 L, P<0.001). Thus, results provide novel preliminary information showing that reducing bedtime variability can improve body composition over time. Given that bedtimes are highly individualized, this may provide an easy public health message to maintain healthy sleep hygiene, particularly stable bedtime routine, to achieve better weight management and reduced CVD risk.