Solar radiation and out-of-hospital cardiac arrest in Japan.

BACKGROUND: Although several studies have estimated the effects of temperature on mortality and morbidity, little is known regarding the burden of out-of-hospital cardiac arrest (OHCA) attributable to solar radiation.

METHODS: We obtained data for all cases of OHCA and meteorological data reported between 2011 and 2014 in 3 Japanese prefectures: Hokkaido, Ibaraki, and Fukuoka. We first examined the relationship between daily solar radiation and OHCA risk for each prefecture using time-varying distributed lag non-linear models and then pooled the results in a multivariate random-effects meta-analysis. The attributable fractions of OHCA were calculated for low and high solar radiation, defined as solar radiation below and above the minimum morbidity solar radiation, respectively. The minimum morbidity solar radiation was defined as the specific solar radiation associated with the lowest morbidity risk.

RESULTS: A total of 49,892 cases of OHCA occurred during the study period. The minimum morbidity solar radiation for each prefecture was the 100th percentile (72.5 MJ/m2 ) in Hokkaido, the 83rd percentile (59.7 MJ/m2 ) in Ibaraki, and the 70th percentile (53.8 MJ/m2 ) in Fukuoka. Overall, 20.00% (95% empirical confidence interval [eCI]: 10.97-27.04) of the OHCA cases were attributable to daily solar radiation. The attributable fraction for low solar radiation was 19.50% (95% eCI: 10.00-26.92), whereas that for high solar radiation was 0.50% (95% eCI: -0.07-1.01).

CONCLUSIONS: Low solar radiation was associated with a substantial attributable risk for OHCA. Our findings suggest that public health efforts to reduce OHCA burden should consider the solar radiation level. Large prospective studies with longitudinal collection of individual data is required to more conclusively assess the impact of solar radiation on OHCA.