Temperature and Mental Health: A Systematic Review and Meta-Analysis

Abstract

Background: The relationship between ambient temperature and mental health outcomes has not been sufficiently synthesised and communicated. Methods: A systematic search included all original studies on humans until 20/03/2020 examining a relationship between ambient temperatures and mental health outcomes (suicide, hospital attendance for mental disorders, community mental health and emotional wellbeing). Databases WebOfScience, Embase, PsychINFO, and PubMed were searched, alongside a limited search of Google Scholar. The risk of bias for individual studies was assessed using the Newcastle-Ottawa Scale (NOS), while the quality of evidence across studies was assessed using the GRADE approach. Findings: 123 studies were included in the review, with 19 studies suitable for meta-analysis. Pooled data on suicide rates (7 articles, N=1,805,734) indicate a risk ratio of 1.01 per 1oC increase in mean temperature (95%CI: 1.00, 1.01), a 1.7% increase (95%CI: 1.1%, 2.3%) in suicide incidence per 1oC temperature rise (5 articles, N=219,096), and a 6.2% (95%CI: 5.2%, 7.2%) increase for each 2-5oC temperature rise (3 articles, N=416,976). Hospital attendance for mental disorders was 9.7% higher (95%CI: 7.6%, 11.9%) during heatwaves than non-heatwave periods (3 articles, N=362,086), with a risk ratio of 1.02 (95%CI: 1.01, 1.03) at the 99th temperature percentile compared with the 50th (3 articles, N=532,296). In qualitative synthesis of the literature, higher ambient temperature (including average temperatures, heatwaves and temperature variation) across multiple time windows were positively associated with increases in attempted and completed suicides (78 studies in this category, >3,976,577 suicide events), increased hospital attendance for mental disorders (33 studies, >6,222,993 hospital attendances), and worse outcomes for community mental health and wellbeing (15 studies, >4,875,006 individuals). Interpretation: Climate change brings increasing ambient temperatures, heatwaves and temperature variation, which are all risk factors for worse mental health outcomes. Health system leaders and policy makers must be adequately prepared. Building resilience to the impacts of increasing temperatures on mental health outcomes in public health and health systems will require equitable and proactive support for those most vulnerable, including individuals with a diagnosable mental disorder, rural populations and those in 'urban heat islands'. Although many LMIC are particularly vulnerable to climate change, only 25 studies were conducted in these regions. More good quality standardised research is required to improve our understanding of the nature, severity, context and modulating factors of these effects. Funding Statement: RT receives a studentship from the National Institute for Health Research (NIHR) School for Public Health Research (PD-SPH-2015). MBT is partially supported by a donation from Marit Mohn to the Mohn Centre for Children’s Health and Wellbeing. No other external funding contributed to the study or researcher's time. Declaration of Interests: None to declare.