Effects of Room Temperature, Socioeconomic Status, and Electricity Usage on Home Morning, Evening, and Sleep Blood Pressure: The Shizuoka Study

Objective: Cold ambient temperatures are known to increase blood pressure (BP), but the influence of room temperature remains understudied. Socioeconomic status and electricity use may also influence BP through room temperature. This study examined the impact of room temperature, household income, and electricity usage in morning, evening, and sleep BP measured at home. Design and method: The cross-sectional 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. Electricity use for each participant was obtained from an electric power company. Socioeconomic status was assessed by a structured questionnaire. 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 one-week average morning BP), 93 were hypertensive on the coldest day. The odds ratio of having hypertension on the coldest day increased linearly with a higher 1-week average morning BP (<115 mmHg: reference, >=115 and <125 mmHg: odds ratio = 6.7, >=125 and <135 mmHg: odds ratio = 15.4, P <0.001). Household income was not directly correlated with morning BP, but it showed an inverse association with morning room temperature via reduced electricity usage. Conclusions: 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.