Effects of high temperatures on poor mental health outcomes: a systematic review and meta-analysis

Abstract

Abstract Background In the context of warming temperature and increased prevalence of mental disorders, a growing body of literature suggests the adverse effects of high temperatures on mental health. However, no study has quantitatively summarised the evidence. This study therefore systematically reviews the epidemiological evidence and summarises the quantitative effects of high temperatures on mental health outcomes, including mortality and morbidity. Methods A systematic search of peer-reviewed epidemiological studies in five databases that linked high temperatures and mental health was conducted on literature published till November 2020. A range of mental health conditions were defined using ICD-10 classifications. We included studies that examined the quantitative association between temperatures and mental health mortality or morbidity (i.e. hospital admissions, emergency presentations) in the general population. Random-effects models were used to summarise the percentage changes in mental health outcomes per 1 °C temperature increase. Results The keyword search yielded 4560 citations from which 34 studies were included in the meta-analysis. For 1 °C increase in temperature, the risk of mental health-related mortality and morbidity increased by 2.2% (95%CI: 1.5-2.9%) and 0.9% (95%CI: 0.7-1.5%). The greatest risk was associated with mortality attributed to substance-related mental disorders (4.6%; 95%CI: 0-10.1%), and organic mental disorders (3.3%; 95%CI: 2-4.6%). A 1 °C temperature rise was also associated with a statistically significant increase in morbidity such as mood disorders, organic mental disorders, and schizophrenia. Higher risk was evident for elderly and populations living in tropical and subtropical climate zones. Conclusions Our results suggest that exposure to high temperatures increases the risk of poor mental health outcomes. These risks will likely increase with a warming climate. Key messages High temperatures are associated with poor mental health outcomes, including mortality and morbidity. The findings reinforce the need for preventive intervention to protect vulnerable populations.