Role of housing in blood pressure control: a review of evidence from the Smart Wellness Housing survey in Japan

Hypertension Research https://doi.org/10.1038/s41440-022-01060-6 REVIEW ARTICLE Role of housing in blood pressure control: a review of evidence from the Smart Wellness Housing survey in Japan Wataru Umishio1,2 Toshiharu Ikaga2 Kazuomi Kario3 Yoshihisa Fujino4 Masaru Suzuki5 Shintaro Ando6 Tanji Hoshi7 Takesumi Yoshimura8 Hiroshi Yoshino9 Shuzo Murakami10 on behalf of the SWH survey group ● ● ● ● ● ● ● ● ● ● 1234567890();,: 1234567890();,: Received: 5 August 2022 / Accepted: 22 September 2022 © The Author(s) 2022. This article is published with open access Abstract Current countermeasures for preventing hypertension emphasize only improvements to lifestyle. Recently, improving life environment has attracted attention, in parallel with publication of the WHO Housing and health guidelines. We quantitatively evaluated the relationship between housing thermal environment and blood pressure (BP) in a real-world setting. We conducted a nationwide, prospective intervention study—the Smart Wellness Housing survey—in Japan, as a non-randomized controlled trial. The intervention was the retrofitting of thermal insulation in houses. Participant recruitment was done by construction companies in all 47 prefectures of Japan. Measurements of home BP and indoor temperature at 1.0 m above the floor in the living room, changing room, and bedroom were taken for 2 weeks before and after the intervention each winter (November–March) of FY 2014–2019. As of July 2022, over 2500 households and 5000 participants were registered in the database. We found that (1) about 90% of Japanese lived in cold homes (minimum indoor temperature <18 °C), (2) indoor temperature was non-linearly associated with home BP, (3) morning systolic BP (SBP) was more sensitive than evening SBP to changes in indoor temperature, (4) SBP was influenced by indoor temperature change particularly in older participants and women, (5) unstable indoor temperature was associated with large BP variability, and (6) insulation retrofitting intervention significantly reduced home BP, especially in hypertensive patients. We proposed that the BP reduction effect of the life-environment is comparable to that achievable by lifestyle. Keywords Blood pressure variability Home blood pressure Housing Indoor temperature Insulation retrofit ● ● ● ● Introduction A list of members and their affiliations appears in the Supplementary Information. Supplementary information The online version contains supplementary material available at https://doi.org/10.1038/s41440022-01060-6. Excess winter mortality (EWM), which refers to the marked increase in mortality rate in winter, is a global problem in public health [1, 2]. Paradoxically, however, studies in Europe [3–5], the USA [6, 7], and Asia [8, 9] have reported * Wataru Umishio 5 Department of Emergency Medicine, Ichikawa General Hospital, Tokyo Dental College, Ichikawa, Chiba, Japan 1 Department of Architecture and Building Engineering, School of Environment and Society, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, Japan 6 Department of Architecture, Faculty of Environmental Engineering, The University of Kitakyushu, Kitakyushu, Fukuoka, Japan 2 Department of System Design Engineering, Faculty of Science and Technology, Keio University, Yokohama, Kanagawa, Japan 7 Tokyo Metropolitan University, Hachioji, Tokyo, Japan 8 University of Occupational and Environmental Health, Kitakyushu, Fukuoka, Japan 9 Tohoku University, Sendai, Miyagi, Japan 10 Institute for Built Environment and Carbon Neutral for SDGs, Hirakawacho, Chiyoda-ku, Tokyo, Japan 3 4 Department of Cardiology, Jichi Medical University School of Medicine, Shimotsuke, Tochigi, Japan Department of Environmental Epidemiology, Institute of Industrial Ecological Sciences, University of Occupational and Environmental Health, Kitakyushu, Fukuoka, Japan W. Umishio et al. Graphical Abstract Hypertension and cardiovascular diseases are not only lifestyle diseases but also life-environment diseases. higher EWM in areas with milder winter climates. One possible explanation for this is that houses in these areas are less adequately prepared for winter conditions. More than half of EWM is caused by cardiovascular disease (CVD) [10], a phenomenon which is partially attributable to coldinduced hypertension. Hypertension is called a “silent killer” as it has almost no subjective symptoms [11]. Indeed, many hypertensive patients are unaware of their hypertension [12]. Reliance on antihypertensive drugs alone might be an inadequate, highrisk strategy—a likely better strategy would involve shifting the BP of the total population in the desirable direction. However, existing population strategies exclusively emphasize improvements to lifestyle, focusing on habits such as physical activity, diet, smoking and alcohol consumption; improving the housing thermal environment has been neglected. In 2018, the WHO issued the Housing and health guidelines, which focused on “low indoor temperatures and insulation” [13]. Based on a systematic review of evidence the guidelines recommend a minimum indoor temperature of 18 °C, stating that low indoor temperature can lead to vasoconstriction—a known risk factor of hypertension—and that retrofitting insulation into existing housing can alleviate the negative effects of low indoor temperature on health. The guidelines call for research to establish the appropriateness of 18 °C as a general target for a minimum indoor temperature or whether this target should vary in different populations. The guidelines also emphasize the desirability of further evidence on the effects of living in a thermally insulated home on health outcomes. Consistent with the above background, we started a nationwide, prospective intervention trial, the “Smart Wellness Housing (SWH) survey” in Japan, to quantitatively evaluate the health effects of indoor temperature and insulation retrofitting of houses. Study design of the Smart Wellness Housing survey The SWH survey was designed with two validation patterns, prepared from short- and long-term viewpoints (Fig. 1). The survey started in winter 2014, and collected all data used in the “before and after insulation study” described below. Construction companies recruited participants throughout all 47 prefectures of Japan, and more than 2500 households and 5000 participants were registered in the SWH survey database as of July 2022. Role of housing in blood pressure control: a review of evidence from the Smart Wellness Housing survey. . . Fig. 1 Overview of the Smart Wellness Housing survey in Japan †FY indicates fiscal year (1) Before and after insulation study [University Hospital Medical Information Network Clinical Trials Registry (UMIN-CTR) Trial No. UMIN000030601] This study was a non-randomized controlled trial with groups categorized according to participants’ choice of whether or not to conduct insulation retrofitting. This intervention included a (...truncated)