High and low ambient temperature at night and the prescription of hypnotics

Study objectives This study investigated the association between ambient nighttime temperature and sleep problems assessed by the prescription dose of sleeping pills in South Korean adults. Methods We used the 2002-2015 National Health Insurance Service-National Sample Cohort. A total of 711,079 adults who were 20 years old or older were included, wherein 42,858 adults (approximately 6%) had been prescribed hypnotic medications including zolpidem (N05CF02) and triazolam (N05CD05). Ambient temperature data was calculated as the mean highest temperature of nighttime (23:00-07:00) for every month from January to December. We combined the drug-prescribed date with the administrative districts-level daily nighttime temperature between 2002 and 2015. Results We found that a non-linear, U-shaped relationship between nighttime temperature and hypnotic medication prescription. With an increase per 1°C temperature or an increase in a square per 1°C, the prescription dose of sleeping pills was significantly increased (both p <0.05). At each 5°C nighttime temperature, subjects belonging to low (≤0°C and 0 – 5°C) or high (20 – 25°C and ≥25°C) temperature categories had significantly higher doses of sleeping pills than those at the reference temperature (10 – 15°C). Changes in nighttime temperature had a significant non-linear effect on the prescribed dosage of hypnotic medications for both adults (p <.0001) and the elderly (p = 0.0006). Conclusion We found that either a high or low nighttime temperature was significantly associated with a high daily dose of hypnotic medications in the Korean population.