Themed Paper – Original ResearchAssociations between high ambient temperatures and heat waves with mental health outcomes: a systematic review
Introduction
Global average temperatures are increasing due to climate change. 2016 was the warmest year on record; the 10 warmest years on record occurred in the past 15 years1 with consensus that this warming is anthropogenic.2
Environmental hazards and disasters are associated with a range of adverse mental health impacts.3 Understanding this risk has been highlighted as a priority in a landmark UN agreement, the Sendai Framework for Disaster Risk Reduction.4 A number of direct impacts have been reported, including suicide epidemics in agriculture workers linked to prolonged drought,5 posttraumatic stress disorder (PTSD), depression after flooding in the UK6 and increased violent suicides at high ambient temperatures.7 Indirect impacts include mental health consequences of migration and displacement after disasters and conflict and reduced health infrastructure spending.7
Common mental disorders such as anxiety and depression are among the greatest health burdens globally.8 Severe mental health problems such as schizophrenia and bipolar disorder are less prevalent8 but still significant in terms of their impact on health. Treatment options for mental ill-health range from primary care interventions to admission and treatment in specialist facilities. The importance of environmental factors on mental health outcomes is beginning to receive attention.9
The fifth assessment report of the Intergovernmental Panel on Climate Change predicted rising temperatures and an increase in the frequency and intensity of heat waves by the mid-21st century.10 This suggests that extreme weather events may happen with greater frequency, such as the 2003 European heat wave that resulted in an estimated 35,000 excess deaths.11 The association between high ambient temperatures and physical illness is well documented;3, 12, 13, 14, 15, 16 mental health has received less attention although the global evidence base is growing.7, 15
The UK Climate Change Risk Assessment 201717 highlights risks to health, well-being and productivity from high temperatures as priority areas for action. It is apparent that a summary of the impacts of heat on mental health would be useful to guide planners and healthcare providers and also highlight evidence gaps. We therefore undertook a systematic review of such impacts to inform guidance on, plans for and response to extreme heat.
The primary objectives of the review were to
- 1.
determine the mental health effects of high ambient temperatures and heat waves on populations;
- 2.
identify the geographic, sociodemographic and other contextual factors that contribute to mental disorder during hot weather;
- 3.
determine whether heat-related mortality is increased among people with known mental health disorders; and
- 4.
identify gaps in knowledge to support targeting of future research.
Section snippets
Methods
A protocol following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidance was registered with PROSPERO (2017 CRD42017076839).
The search was limited to human studies without date limit. All English language studies were considered from all countries, languages and contexts.
Results
A total of 9300 records were identified, of which 8716 remained after removal of duplicates. One additional article was supplied by topic experts which outlined hospital admissions during heat waves in Vietnam.21 Of 8728 total records, 8640 records were excluded at title and abstract review as they were not within the scope of this review. A total of 88 full texts were reviewed, of which 35 were kept (Fig. 1).
Thirty-four observational studies and one case–control study were included. The
Discussion
This review has summarised the evidence of association between higher temperatures and mental health outcomes, describing the size and direction of association and correlation where available. To the best of our knowledge, this is the first attempt to summarise the available evidence on this area and has corroborated previous studies and commentaries.7 Higher temperatures increased the risk of all mental health outcomes for which evidence was found. Significant gaps exist in evidence for the
Ethical approval
Not required as this was a review of the published literature.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Competing interests
The authors have no competing interests to declare.
References (72)
- et al.
Impact of heatwave on mortality under different heatwave definitions: a systematic review and meta-analysis
Environ Int
(2016) - et al.
Association between completed suicide and environmental temperature in a Mexican population, using the Knowledge Discovery in Database approach
Comput Methods Programs Biomed
(2016) - et al.
Association between daily environmental temperature and suicide mortality in Korea (2001-2005)
Psychiatry Res
(2011) - et al.
Suicide rates and the association with climate: a population-based study
J Affect Disord
(2006) - et al.
Seasonality and climatic associations with violent and nonviolent suicide: a population-based study
Neuropsychobiology
(2008) - et al.
Seasonal variations in bipolar disorder admissions and the association with climate: a population-based study
J Affect Disord
(2007) - et al.
Effects of climate on admission rates of schizophrenia patients to psychiatric hospitals
Eur Psychiatry
(2005) - et al.
A significant correlation between ward temperature and the severity of symptoms in schizophrenia inpatients–a longitudinal study
Eur Neuropsychopharmacol
(2007) - et al.
Short-term association between environmental factors and hospital admissions due to dementia in Madrid
Environ Res
(2017) - et al.
Effect of some climatic factors on violent and non-violent suicides in Belgium
J Affect Disord
(1992)
Seasonal variations in hospital admissions for mania: examining for associations with weather variables over time
J Affect Disord
Consensus on consensus: a synthesis of consensus estimates on human-caused global warming
Environ Res Lett
Climate change 2014: synthesis report. Contribution of Working Group II to the fifth assessment report of the Intergovernmental Panel on Climate Change
Sendai framework for disaster risk reduction 2015–2030
Suicide and drought in new South Wales, Australia, 1970–2007
Proc Natl Acad Sci USA
The English national cohort study of flooding and health: cross-sectional analysis of mental health outcomes at year one
BMC Public Health
The impact of climate change on mental health (but will mental health be discussed at Copenhagen?)
Psychol Med
Global, regional, and national incidence, prevalence, and years lived with disability for 301 acute and chronic diseases and injuries in 188 countries, 1990–2013: a systematic analysis for the Global Burden of Disease Study 2013
Lancet
Near-term climate change: projections and predictability
The 2003 heat wave
Eurosurveillance
Models for the relationship between ambient temperature and daily mortality
Epidemiology
Heat-related and cold-related deaths in England and Wales: who is at risk?
Occup Environ Med
Ambient temperature and morbidity: a review of epidemiological evidence
Environ Health Perspect
Human health: impacts, adaptation, and co-benefits
UK climate change risk assessment 2017 synthesis report: priorities for the next five years
Endnote X7
Heatwaves and hospital admissions for mental disorders in Northern Vietnam
PLoS One
Seasonal associations between weather conditions and suicide - evidence against a classic hypothesis
Am J Epidemiol
Association of meteorological factors with suicide
Acta Psychiatr Scand
Effects of temperature variation on suicide in five U.S. counties, 1991-2001
Int J Biometeorol
Association of weekly suicide rates with temperature anomalies in two different climate types
Int J Environ Res Public Health
Environmental temperature increase and its possible association with suicide in the population of Baja California Sur (BCS) 1985-2008
Salud Ment
Cited by (201)
Spatial distribution of heat vulnerability in Toronto, Canada
2024, Urban ClimateHealth risks from extreme heat in China: Evidence from health insurance
2024, Journal of Environmental ManagementMaternal health outcomes associated with ambient air pollution: An umbrella review of systematic reviews and meta-analyses
2024, Science of the Total Environment