A warmer indoor environment in the evening and shorter sleep onset latency in winter: The HEIJO-KYO study

Abstract

Difficulty in initiating sleep is an important problem because it is associated with an increased incidence of depression, diabetes, myocardial infarction, and higher all-cause mortality. Although experimental studies in controlled settings have shown that warm skin temperature of the extremities (feet and hands) before bedtime is associated with shorter sleep onset latency (SOL), evidence from real life situations is limited. We assessed the relationship between indoor temperatures in the evening (2h before bedtime) and SOL among 861 home-dwelling elderly participants. Subjective SOL was determined according to a self-administered sleep diary. Actigraphic (objective) SOL, indoor temperature, and bed temperature were simultaneously measured at participants' homes for 48h during the colder seasons (October-April). The association between evening indoor temperature and SOL was assessed using a multilevel linear regression model with random intercept for individual participants. Evening indoor temperature showed a significant inverse association with log-transformed subjective SOL (β=-0.021, P<0.01) and actigraphic SOL (β=-0.019, P<0.01), independent of potential confounders including gender, insomnia medication, evening physical activity, and bedtime. Higher bed temperature during the 2h after bedtime was significantly associated with shorter log-transformed actigraphic SOL (β=-0.028, P<0.01). These significant associations were maintained even after adjustment for evening outdoor temperature. The clinically important findings of the present study indicate that SOL may be shortened by modification of evening indoor temperature and bed temperature for 2h after bedtime.

A Review of the Relation between Household Indoor Temperature and Health Outcomes

“…This means that most studies take into consideration the influence and interconnection with outdoor temperatures or climate (link 1). The higher relevance assigned to socioeconomic factors-indoor temperature and indoor temperature-health outcome (links 4 and 5) socioeconomic factor-indoor temperature [27,29,[39][40][41][42][43][44][45][46][47][48][49][50] Energies 2020, 13, x FOR PEER REVIEW 7 of 23…”

“…The influence of outdoor temperatures on the indoor environment has been assessed in studies such as Uejio et al [39] and Osman et al [40]. Several studies such as [41][42][43][44] have stressed that indoor temperatures were more significantly related to a given health indicator than the outdoor temperature.…”

“…For instance, amongst the health outcomes, the least focused category is that of mental health disorders, with a thinner flux. However, its increasing relevance is recognised, as it is mentioned in studies that address diverse health outcomes, such as nocturia health indicator directly assessed by Saeki et al [42] or sleep onset latency (SOL) or difficulty in falling asleep assessed by Saeki et al [41].…”

“…Table 1 presents the studies addressing each one of the links described in Figure 3 and 264 summarises the identified energy efficiency-indoor temperature-health outcomes. [22] energy efficiency upgrade-low indoor temperature-emergency hospital admissions cardiovascular and respiratory conditions and injuries [27] energy efficiency upgrade-low indoor temperature-cardiovascular and respiratory health related conditions outdoor temperature-cardiovascular and respiratory-related mortality and morbidity [29] high indoor temperature-emergency hospital admissions cardiovascular and respiratory conditions; psychosocial impacts [39] low indoor temperature-emergency care for cardiovascular and respiratory conditions [40] low indoor temperature-cardiovascular and mental health related biomarkers [41] low indoor temperature-cardiovascular and mental health related biomarkers [42] low indoor temperature-cardiovascular and mental health related biomarkers [43] low indoor temperature-cardiovascular related biomarkers [44] high indoor temperature-heat-related health symptoms [45] low indoor temperature-long term health disabilities [46] energy efficiency upgrades-low indoor temperature cardiovascular and respiratory-related mortality [47] energy efficiency upgrade-low indoor temperature general health; respiratoryrelated conditions and general practitioner's hospital admissions [48] energy efficiency upgrade-low indoor temperature-respiratory related conditions, general health status hospital admissions [49] low indoor temperature-cardiovascular related biomarkers [50] low indoor temperature-cardiovascular related biomarkers…”

Biological Effects of Negatively Charged Particle-Dominant Indoor Air Conditions

“…Moreover, the lavatory is also cold. Consequently, there is a risk of changes in blood pressure and the onset of cardiovascular events caused by drastic changes in room temperature in these areas [4,5].…”