Intervention study of the effect of insulation retrofitting on home blood pressure in winter: a nationwide Smart Wellness Housing survey

Objective: The WHO's Housing and health guidelines (2018) listed 'low indoor temperatures and insulation' as one of five priority areas, and indicated insulation retrofitting to help mitigate the effect of low indoor temperatures on health. However, there is still not enough evidence for the effect of insulation retrofitting based on an objective index. Methods: We conducted a nonrandomized controlled trial comparing home blood pressure (HBP) between insulation retrofitting (942 households and 1578 participants) and noninsulation retrofitting groups (67 households and 107 participants). HBP and indoor temperature were measured for 2 weeks before and after the intervention in winter. To examine the influence of insulation retrofitting on HBP, we used multiple linear regression analysis. Results: The analyses showed that indoor temperature in the morning rose by 1.4 degrees C after insulation retrofitting, despite a slight decrease in outdoor temperature by 0.2 degrees C. Insulation retrofitting significantly reduced morning home SBP (HSBP) by 3.1 mmHg [95% confidence interval (95% CI): 1.5-4.6], morning home DBP (HDBP) by 2.1 mmHg (95% CI: 1.1-3.2), evening HSBP by 1.8 mmHg (95% CI: 0.2-3.4) and evening HDBP by 1.5 mmHg (95% CI: 0.4-2.6). In addition, there was a dose-response relationship between indoor temperature and HBP, indicating the effectiveness of a significant improvement in the indoor thermal environment. Furthermore, there was heterogeneity in the effect of insulation retrofitting on morning HSBP in hypertensive patients compared with normotensive occupants (-7.7 versus -2.2 mmHg, P for interaction = 0.043). Conclusion: Insulation retrofitting significantly reduced HBP and was more beneficial for reducing the morning HSBP of hypertensive patients.