Given the rapid ageing of the Japanese population, it is important to identify strategies to minimise the gap between healthy life expectancy and average life span. Cold-related injuries and symptoms have recently attracted attention, and studies on the relationship between blood pressure, falls, physical performance, and the thermal environment of housing have been reported. Based on previous studies, we hypothesised that people living in cold homes will receive certification for long-term care insurance earlier in life, indicating a shorter healthy life expectancy.
This retrospective study involved 205 community-dwelling older adults living in Japan. Participants completed a self-report questionnaire about personal characteristics, housing, and perceived indoor temperature in their home during winter. Participants were divided into a Cold group and a Warm group based on perceived indoor temperature. Mean and minimum living room and bedroom temperatures differed between the Cold group and Warm group. On the other hand, mean, maximum, and minimum temperatures in the dressing room all differed significantly between the Cold group and the Warm group. Air conditioners were the only heating system that contributed to warmer indoor temperature. Maximum temperature was higher but minimum temperature was lower in houses with fan heaters, which may run intermittently and with short running time. Houses in which kotatsu systems or electric blankets were used tended to have colder indoor temperatures in the living room and bedroom.
The Kaplan-Meier method was used to analyse the relationship between age at certification for needing long-term care insurance and perceived indoor temperature. Mean age at certification was 77.8 years in the Cold group and 80.6 years in the Warm group (p<0.01, generalised Wilcoxon test). Multivariate analysis by ANCOVA revealed a significant main effect of perceived indoor temperature, with the Cold group having a younger age at certification for needing long-term care (F(1, 197)=9.27, p<0.01). Estimated marginal means indicated that healthy life expectancy was 2.9 years shorter in the Cold group than in the Warm group even after adjusting for participant characteristics. When the relationship between measured indoor temperature and age at certification was tested, people living in houses with low indoor temperature (<14 °C) or high indoor temperature (≥18 °C) had a higher age at long-term care certification. People with low indoor temperature might spend longer time outside and use heating systems for shorter time. Since we could not grasp or control times going-out or using heating system, we conclude that relationship between measured indoor temperature and age at certification can support the previous result though, close investigations of indoor thermal environment in where older people lives are still needed.
Our findings suggest that maintaining an appropriate indoor thermal environment could help prevent the need for long-term care.
