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This study investigated the relationship between perceived indoor temperature in winter and frailty among community-dwelling older people. This cross-sectional study included 342 people 65 years and older in Japan. Participants answered questions about demographics, frailty, housing, and perceived indoor temperature in winter. Participants were grouped based on perceived indoor temperature (Cold or Warm) and economic satisfaction (Unsatisfied or Satisfied). Differences in the frailty index between perceived indoor temperature groups and economic satisfaction groups were tested by using ANCOVA and MANCOVA. An interaction effect showed that people in the Cold Group and unsatisfied with their economic status had significantly higher frailty index scores (F(1, 336) = 5.95, p = 0.015). Furthermore, the frailty index subscale of fall risk was the specific indicator of frailty that accounted for this significant relationship. While previous research has shown the risks related to cold indoor temperature in homes, interestingly among those who reported cold homes, only those who were not satisfied with their economic situation reported being at increased risk for frailty. This highlights the potential importance of preventing fuel poverty to prevent frailty.

Background In modern society, humans spend 60–70% of their time at home, housing environment is of great importance to health. In support of the importance, WHO issued Housing and Health Guidelines in 2018. The guidelines show that cold indoor temperatures have adverse health consequences, and suggest a recommended indoor temperature of 18°C. However, it is unclear who lives in cold homes in real-world settings. We aimed to examine “what are the common characteristics of residents who live in low-indoor-temperature environments.” Methods We conducted a nationwide survey on indoor temperature who intended to conduct insulation retrofitting in Japan. Indoor temperature was measured in the living room, bedroom, and changing room for 2 weeks in winter seasons (November−March) of 2014 to 2019. The relationship between characteristics of residents and living room temperature was analyzed using a multilevel model. Results Cross-sectional analyses involving 2,190 households showed that the average temperature in the living room, bedroom and changing room was 16.8°C, 12.8°C and 13.0°C, respectively. Living room temperature was highest (19.8˚C) in Hokkaido, where outdoor temperatures are lower than in other areas, and lowest (13.1˚C) in Kagawa, which is considered to have a mild climate. A multilevel analysis showed that the odds ratio for living room temperature in the morning falling below 18˚C was 1.38 (95% CI: 1.04−1.84) for the middle income group and 2.07 (95% CI: 1.28−3.33) for the low income group, compared to the high income group. The odds ratio was 1.96 (95% CI: 1.19−3.22) for single-person households, compared to households living with housemates. Furthermore, lower room temperature was also correlated with kotatsu (traditional Japanese local heating device) use and a larger amount of clothes. Conclusions There were disparities in living room temperature within Japan, and they related to socioeconomic status, single-person households and the way of living. These housing disparities have the potential to cause health disparities. We expect these results will be useful in the development of prevention strategies for residents who live in cold homes and the reduction in health disparities.