Objective: Mortality due to cardiovascular disease rises sharply in winter. Known as excess winter mortality, this phenomenon is partially explained by cold exposure-induced high blood pressure. We aimed to analyze the relationship between indoor temperature and blood pressure.
Design and Method: A survey was administered to households receiving subsidies for insulation retrofit as part of a non-randomized controlled trial. We collected data on the indoor environment and home blood pressure (HBP) of participants before and after insulation retrofit in winter. HBP was measured by participants twice daily, in the morning and evening, for two weeks. Data from the baseline survey in winter were obtained from 1,663 households and 3,001 participants. We analyzed the relationship between indoor thermal environment and HBP using a multilevel linear regression model with random intercepts, in which repeatedly measured day-level variables obtained from actual measurements (e.g., living room temperature, quality of sleep) were nested within individual-level variables obtained from the questionnaire survey (e.g., age, sex, body mass index, vegetable consumption, alcohol consumption, smoking status). The objective variable was systolic BP (SBP) in the morning (n = 50,155).
Results and Conclusion: There was a nonlinear relationship between morning SBP and living room temperature. The effect of room temperature on SBP was reduced at low and high room temperatures. Participants aged 57 years (mean age in this survey) had an average morning SBP increase of 6.5 mm Hg per 10°C decrease in living room temperature. The temperature disparity between the living room and bedroom also affected SBP. There was a significant interaction between age and temperature, indicating a stronger effect of indoor temperature on SBP in older residents. These findings indicate that residents at high risk of cardiovascular events should maintain the indoor temperature within an appropriate range. They may also have important implications for managing hypertension and preventing cardiovascular events.
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