According to statistical data reported by the Japanese government, the major causes of death for Japanese people are cancer, heart disease and cerebrovascular disease. The incidence rate of cerebrovascular disease in particular is higher during winter than summer (Hayama, 2011). One possible reason for this seasonal difference is that exposure to low temperatures can cause fluctuations in blood pressure. In houses with poor thermal insulation, indoor temperature differences between heated and non-heated spaces, such as the bathroom, corridors, and lavatory can be larger during winter. Many houses in the Tohoku region have a poor thermal environment during winter, and the incidence rate of cerebrovascular disease in this area is the highest compared to the other areas in Japan. Hasegawa and Yoshino (1985) investigated indoor thermal environment in houses of Yamagata prefecture, which is included in Tohoku region, during the heating season and the death rate of cerebrovascular disease in 1983 and 1984. As a result, the temperature difference between the heated living room and the unheated rooms was found to be great. Also it was revealed that if the lavatory temperature was low or the bedroom was not heated, the occupants living in such houses statistically tended to be susceptible to cerebral vascular accident.
In order to clarify the association between the indoor environment of residential buildings and cerebrovascular disease, an epidemiological survey of 188 elderly persons living in Yamagata Prefecture in the Tohoku region of Japan was conducted. The specific areas investigated included three rural towns (former Yahata town, former Haguro town and Asahi town) and these areas are same as the investigated areas about 30 years ago. The survey was divided into three phases. The first phase (Phase 1) was a cross-sectional questionnaire on housing characteristics related to the indoor thermal environment and occupants' lifestyle habits among elderly persons. This paper describes the results obtained from this questionnaire and presents the characteristics of the indoor thermal environment and occupants' lifestyle habits during winter. Moreover, an association between the increase in rate of death due to cerebrovascular disease and factors that influenced the indoor environment of houses is examined using multivariable logistic regression analysis.
The multivariable logistic regression analysis shows that always feeling a draft in the living room while operating heating equipment (AOR, 8.14; 95%CI, 1.55-42.8) and low temperature in a living room at morning (AOR, 0.87; 95%CI, 0.78-0.98) was positively associated with an increased rate of death due to cerebrovascular disease for former Yahata town. These results indicate that a poor indoor thermal environment may contribute to an increase in the rate of death due to cerebrovascular disease. In addition, a high salt diet may contribute to the onset of cerebrovascular disease. When participants moved from a living room to a bathroom during winter, they reported thermal sensations, such as ‘warm’, ‘neutral’ and ‘cold’. AOR for ‘cold’ when entering a bathroom (AOR, 0.17; 95%CI, 0.05–0.58) was significant for former Yahata. These results indicate that occupants in this town did not feel cold, although the indoor temperatures among surveyed towns were similar. AOR for light clothing when staying at home was significant for former Yahata town and participants were thinly dressed during heating season. Therefore they may be more readily exposed to a cold indoor environment than other towns.
