0102 Effects of Daytime Ambient Temperature on Actigraphy-derived Sleep Parameters in Men and Women

Abstract Introduction Evening and nocturnal exposure to cold and warm temperature can respectively blunt or enhance vasodilation needed to initiate sleep. However, the effects of temperature exposure several hours prior to bedtime on sleep have not been well studied. We examined the impact of colder and warmer daytime temperatures on nighttime sleep in men and women. Methods In a 7 to 13-day inpatient study (NCT01568671), the metabolism of twelve men (23.2 ± 4.9 yrs; 23.4 ± 1.6 kg/m2) and fifteen women (25.5 ± 4.0 yrs; 22.1 ± 2.2 kg/m2) was measured in a room calorimeter during exposure to a randomly assigned temperature between 16-31˚C from 0800-1300 each day while wearing standardized clothing. Thereafter, ambient temperature was controlled at a thermal neutral temperature (23-25˚C), including during nighttime sleep. Diet and physical activity each day were also standardized. Sleep parameters were assessed using the wrist actigraphy on the non-dominant hand (ActiGraph wGT3X-BT; 80Hz) and compared amongst thermal neutral (24.3 ± 0.4˚C), coldest (19.1 ± 1.2˚C), and warmest (30.4 ± 0.7˚C) daytime temperatures. Whole-body thermal insulation was calculated as the inverse of the slope of metabolism versus ambient temperature below the thermal neutral zone. Linear mixed effects models were used to predict each sleep parameter with sex and temperature as fixed effects and each subject as a random effect. Results Over all temperatures, women spent longer time in bed (460.1 ± 58.6 vs. 405.1 ± 68.9 min, p=0.01) and slept longer (427.3 ± 54.1 vs. 372.3 ± 62.0 min p=0.007). No significant interaction was observed between sex and temperature for the sleep parameters. Sleep efficiency after cold exposure was significantly correlated with insulation (R=0.45, p=0.03), which was greater for women than men (0.38 ± 0.04 vs. 0.34 ± 0.04°C/W/m2, p< 0.04). No differences in sleep parameters were observed after warm exposure. Conclusion Our findings suggest that daytime cold exposure may influence nocturnal sleep in a relationship mediated by individual thermal insulation. Future studies will need to assess sleep architecture and skin and core temperature regulations of men and women in response to daytime ambient temperature. Support (if any)