The shifted focus of interest in the temperature—blood pressure relationship: from load to variability

The contribution of Umishio et al. [ 1 ] is an important step forward for at least three reasons: first, data clearly show that morning-evening blood pressure (BP) difference, a measurement of BP variability that can easily be self-measured at home, is closely related to the variation in temperature, thus moving the focus from Ambulatory Blood Pressure Monitoring (ABPM) to Home Blood Pressure (HBP) monitoring; second, the prevailing effect of indoor over outdoor temperature in inducing changes in BP variability clearly emerges; and third, the project will offer the government of Japan a measure of the health effects of insulation retrofitting, a structural housing intervention. The Smart Wellness Housing (SWH) project is indeed aimed at quantitatively evaluating the relationship between indoor temperature and home BP (HBP) in Japan among participants who lived in houses that did not meet the S (Supreme) standards of the “Act on the Promotion of Dissemination of Long-Lasting Quality Housing” in Japan and decided to conduct insulation retrofitting. Therefore, the present data can be considered the baseline observation of a national intervention for health promotion in Japan. Cold housing, below the World Health Organization’s recommended minimum of 18 °C [ 2 ], has been associated with avoidable excess winter mortality [ 3 ]. Interventions involving insulation retrofitting have been performed at national levels in several countries worldwide. Moreover, recently, the EU Commission included funds for renovation of housing insulation in “The Recovery and Resilience Facility” project. Although health researchers built a solid foundation for housing interventions, they rarely followed the projects very closely, and the measures of efficacy on health promotion are limited [ 4 ]. The study is therefore a sign of the great work carried out by Japanese clinical researchers in the field of climate health in recent years.