Association between Ambient Temperature and Cause-Specific Cardiovascular Disease Admissions in Japan: A Nationwide Study

Abstract

Background: Substantial evidence suggests that non-optimal temperatures can increase the risk of cardiovascular disease (CVD) mortality and morbidity; however, limited studies have reported inconsistent results regarding hospital admissions depending on study locations, which also lack national-level investigations on cause-specific CVDs.

Methods: We performed a two-stage meta-regression analysis to examine the short-term associations between temperature and acute CVD hospital admissions by specific categories [i.e., ischemic heart disease (IHD), heart failure (HF), and stroke] in 47 prefectures of Japan from 2011 to 2018. First, we estimated the prefecture-specific associations using a time-stratified case-crossover design with a distributed lag nonlinear model. We then used a multivariate meta-regression model to obtain national average associations.

Results: During the study period, a total of 4,611,984 CVD admissions were reported. We found cold temperatures significantly increased the risk of total CVD admissions and cause-specific categories. Compared with the minimum hospitalization temperature (MHT) at the 98th percentile of temperature, the cumulative relative risks (RRs) for cold (5th percentile) and heat (99th percentile) on total CVD were 1.226 [95% confidence interval (CI): 1.195, 1.258] and 1.000 (95% CI: 0.998, 1.002), respectively. The RR for cold on HF [RR=1.571 (95% CI: 1.487, 1.660)] was higher than those of IHD [RR=1.119 (95% CI: 1.040, 1.204)] and stroke [RR=1.107 (95% CI: 1.062, 1.155)], comparing to these corresponding MHTs by the specific causes. We also observed that extreme heat increased the risk of HF with RR of 1.030 (95% CI: 1.007, 1.054). Subgroup analysis showed that the age group ≥ 85-year was more vulnerable to these non-optimal temperature risks.

Conclusions: This study indicated that cold and heat exposure could increase the risk of hospital admissions for CVD, varying depending on the cause-specific categories, which may provide new evidence to reduce the burden of CVD.

Note:
Funding Declaration: RP was supported by a grant from the China Scholarship Council (Grant Number 201906230329). YK was supported by the University of Tokyo Excellent Young Researcher. This work was also supported by grants from the Ministry of Health, Labour and Welfare, Japan (21AA2007 and 22AA2003), and the Ministry of Education, Culture, Sports, Science and Technology, Japan (20H03907).

Conflict of Interests: The authors declare they have no actual or potential competing financial interests.

Keywords: Temperature, Cardiovascular disease, Hospital admissions, Morbidity