Effects of room temperature on home morning, evening, and sleep blood pressure: the Shizuoka study.

Background: Cold ambient temperatures are known to increase blood pressure (BP), but the influence of room temperature remains understudied. This study examined the impact of room temperature in morning, evening, and sleep BP measured at home.

Methods: The study included 779 adults (mean age: 70.7 years) from a community-based longitudinal study. Home BP was measured for 1 week using a conventional cuff-oscillometric device, whereas sleep BP was automatically recorded at 00 : 00, 02 : 00, and 04 : 00 using a timer-equipped BP monitor. Room temperature was measured concurrently using a thermometer in the BP monitor.

Results: A 1°C decrease in room temperature increased morning systolic and diastolic BPs by 0.863 and 0.342 mmHg, respectively ( P  < 0.001). The evening systolic and diastolic BPs increased by 0.721 and 0.320 mmHg, respectively ( P  < 0.001). However, sleep systolic (0.076 mmHg, P = 0.181) and diastolic (0.078 mmHg, P  = 0.039) BPs showed weaker associations. The association between morning systolic and diastolic BPs remained significant after adjusting for ambient temperature (0.809 and 0.304 mmHg, respectively; P  < 0.001). Age was the only factor associated with room temperature-related BP changes. Among 433 normotensive individuals (based on 1-week average morning BP), 93 were hypertensive on the coldest day. These participants had higher average morning BPs within the normal range and were more likely to use antihypertensive medication.

Conclusion: Room temperature significantly influenced home morning and evening BPs but not sleep BP, independent of ambient temperature. Maintaining appropriate room temperatures may aid in BP management at home.