Background: Higher cardiovascular mortality in winter may be partly explained by increased blood pressure (BP) because of cold exposure. However, this winter excess mortality is higher in countries with moderate winter than those with severe winter climate.
Objectives: Although higher BP in low outdoor temperatures has been reported, the magnitude of association of indoor temperature with ambulatory BP remained unclear. We aimed to compare the associations of indoor and outdoor temperature with ambulatory BP.
Methods: From repeated measurements on two consecutive days during colder months (October–April) among 868 elderly individuals, we assessed the association of indoor and outdoor temperatures with ambulatory BP using multilevel analysis with random intercept for each individual.
Results: Correlation between indoor and outdoor temperature got weak along with decreasing outdoor temperature. Outdoor temperature was not significantly associated with ambulatory BP. In contrast, a 1°C lower indoor temperature was significantly associated with 0.22 mmHg higher daytime SBP, 0.18% higher nocturnal BP fall, 0.34 mmHg higher sleep-trough morning BP surge independent of potential confounders including physical activity. The models with indoor temperature showed better fit of the model than those with outdoor temperature. Night-time SBP did not show significant association with indoor and outdoor temperature but with bed temperature.
Discussion: Our results suggest the importance to assess the association of indoor temperature with cardiovascular mortality to determine whether improving housing thermal environment reduces winter excess mortality.
Conclusion: Indoor temperature showed stronger association than outdoor temperature with BP in colder months.
aDepartment of Community Health and Epidemiology, Nara Medical University School of Medicine
bDepartment of Nursing, Tenri Healthcare University
cCenter for Academic Industrial and Governmental Relations, Nara Medical University School of Medicine, Nara, Japan
Correspondence to Keigo Saeki, MD, PhD, Department of Community Health and Epidemiology, Nara Medical University School of Medicine, 840 Shijocho, Kashiharashi, Nara 634-8521, Japan. Tel: +81 744 29 8841; fax: +81 744 29 0673; e-mail: firstname.lastname@example.org
Abbreviations: PA (physical activity), physical activity at BP measurements using actigraph; prewaking MBPS (morning blood pressure surge), morning BP − prewaking BP; sleep-trough MBPS (morning blood pressure surge), morning BP – lowest night-time BP; Tempamb, (ambient temperature) indoor temperature (temperature in the living room or bedroom) while participants were at home or the outdoor temperature while participants were out of their homes according to self-reported diaries; Tempin, (indoor temperature) temperature measured in participants’ living room (daytime) or bedroom (in night-time) at 10-min intervals; Tempout, (outdoor temperature) temperatures measured at local meteorological office at 10-min intervals
Received 3 September, 2013
Revised 31 March, 2014
Accepted 31 March, 2014
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