A systematic review of the impacts of extreme heat on health and wellbeing in the United Kingdom

Figures & data

Table 1. Search strategy for extreme heat.

Population Location	United Kingdom OR UK, OR Great Britain OR Wales OR England OR Scotland OR Northern Ireland OR Britain
	AND
Indicators for exposure to extreme heat	Extreme heat OR Temperature OR Hot temperature OR Indoor adj3 heat* OR Indoor adj3 threshold OR Indoor adj3 thermal OR Indoor adj3 climate OR Ambient adj3 temperature* OR Residential adj3 temperature OR Heat OR urban heat OR UHIE
	AND
Health outcomes	Accident OR asthma OR ‘blood pressure’ OR cardiovascular OR COPD OR CVD OR death OR disability OR disorder OR ‘emotional health’ OR ‘health outcome’ OR health OR illness* OR ‘injury prevent*’ OR ‘life satisfaction’ OR ‘medical condition*’ OR ‘mental health’ OR Anxiety OR posttraumatic OR ‘Moderate-vigorous physical activity’ OR MVPA OR obes* OR physical activity OR physical health OR sedent* OR suicide OR violence OR independence OR mobility OR safety OR fall OR depression OR isolation OR fire OR ‘electrical hazards’ OR wellbeing OR excess summer death OR heatstroke OR heat exhaustion OR dehydration OR Stress OR respiratory OR autoimmune triggers OR inequalities
	AND
Studies	Any that contain the desired outcomes

Figure 1. PRISMA flow chart.

Figure 2. Breakdown of outcome measures across 16 included studies.

Table 2. Main findings from studies on extreme heat and mortality.

Study, location	Study design	Aim(s)	Exposure	Main findings	Quality of study
Vardoulakis et al. (2014) England, Wales and Australia	Secondary data analysis- time series	Study to compare the mortality associated with heat and cold in UK regions and Australian cities for current and projected climates and populations	Ambient temperature and relative humidity were downloaded for the British Atmospheric data (England and Wales). Daily mean temperature and relative humidity was calculated. Projected monthly mean temperatures for 2020-2029, 2050-2059, and 2080-2089 were obtained from the UK Climate Impacts Programme.	Analysis of the data for England and Wales showed that the estimated national-level percentage change in mortality associated with exposure to heat was 2.5% (95% CI: 1.9, 3.1) per 1°C rise in temperature above the heat threshold (93rd percentile of daily mean temperature, average of lags 0-1) Findings show that the annual mean heat-related mortality was estimated to increase overall by approximately 90% between the 2020s and 2050s (125% with population projections), and by approximately 72% between the 2050s and 2080s (95% with population projections) under the medium emissions scenario	Moderate
Hajat et al. (2014). UK	Secondary data analysis- time series	Study to estimate temperature-related health burdens for the UK during the 2020s, 2050s and 2080s.	Outdoor measurements of temperature and relative humidity were obtained from the British Atmospheric Data Centre. Daily mean temperature and relative humidity series representative of each region	Findings show that at the national level, there was a 2.1% (95% CI 1.5 to 2.7) increase in mortality for every 1°C rise in temperature above the heat threshold. London RR= 1.04(1.03-1.04)and East Midlands RR=1.03(1.02=1.03) were the region’s most vulnerable to heat. The mean estimate of heat-related mortality increases by approximately 66%, 257% and 535% in the 2020s, 2050s and 2080s, respectively, from a current baseline of around 2000 deaths	Strong
Pattenden et al. (2010). England and Wales	Secondary data analysis over 10 years	Study to assess the effects of ozone, heat, and their interaction, on mortality (respiratory, cardiovascular and all-cause mortality) in Britain.	For each conurbation, data from corresponding urban background air quality monitoring stations (obtained from the UK Air Quality Archive) and meteorological stations (from the British Atmospheric Data Centre), were used to construct daily exposure variables	Findings showed that heat remained independently associated with deaths in all three causal subgroups, with the mean rate ratio for respiratory mortality reaching 1.139 (1.079-1.202), cardiovascular diseases (1.055 (1.025 to 1.087), and all-cause mortality 1.071 (1.050 to 1.093).	Moderate
Arbuthnott et al. (2020). Greater London, the West Midlands and Greater Manchester	Secondary data analysis- ecological time series regression analysis	Study to (a) to determine the nature of the relationship between YLL and temperature in the studied conurbations, (b) to estimate (and compare) the proportion of total yearly mortality and YLL attributable to heat and cold	Daily mean temperature obtained from the UK Met Office UKCP09 gridded observation datasets	Findings show that in London, each 1°C above the heat threshold the risk of mortality increased by 3.9% (CI 3.5%, 4.3%)	Strong
Gasparrini et al. (2012). England and Wales	Secondary data analysis- time series/England and Wales	Study to assess heat-related mortality with a wide range of causes using data for England and Wales in the period 1993-2006.	Data on minimum and maximum dry-bulb and dew point temperatures were obtained from the British Atmospheric Data Centre. Relative humidity was calculated using the average from dew point and dry-bulb temperatures at 9:00 h and 15:00 h	Findings show evidence of increased mortality with increasing temperature for almost all cause-of-death groups examined. The overall increase in all-cause mortality was 2.1% (95% CI 1.6% to 2.6%) for a 1°C rise above the regional heat threshold. Among the main causes, the steepest increase in risk was for respiratory mortality (+4.1% (3.5% to 4.8%) per 1°C). Findings for mortality from cardiovascular causes (+1.8% (1.2% to 2.5%)) and myocardial infarction (+1.1% (0.7% to 1.5%)), arrhythmias (+5.0% (3.2% to 6.9%)) and pulmonary heart disease (+8.3% (2.7% to 14.3%). Among non- cardiorespiratory causes, the strongest effects were for genitourinary (+3.8% (2.9% to 4.7%)) and nervous system (+4.6% (3.7% to 5.4%)) disorders. 33.9% of heat deaths were attributable to cardiovascular causes, 24.7% to respiratory causes and 41.3% to all other causes combined	Moderate
Murage et al. (2020) London	Secondary data analysis- Case-crossover	Study to investigate how urban vegetation, housing characteristics and socio-economic factors modify the association between heat exposure and mortality in a large urban area.	Four-hourly temperature data were collected across a 500m resolution grid from a central London location. The four-hourly temperature were aggregated to give a 24 hour mean temperature. Analysis was limited to summer months (May to September)	A total of 185,397 deaths were registered during the study period. The median summer daily temperature was 15.34°C (5.52-26.08°C). Lower daily temperatures were recorded in areas with more trees and vegetation cover and where the proportion of properties owned outright was highest. The highest daily mean temperatures were recorded in areas with a high proportion of social housing, higher income and employment deprivation and in areas with a high proportion of non-native English speakers Findings show that mortality was lowest in the quartile with the lowest indoor temperature 1.034, 95%CI= 1.027-1.041 and highest in the quartile with the highest indoor temperature 1.042, 95%CI= 1.035-1.049. The difference between the ‘best’ and ‘worst’ quartile was greatest in the natural environment measures; tree cover (OR, 95%CI =1.033, 1.026-1.039 vs. 1.043, 1.037-1.050) and vegetation index (1.032, 95%CI= 1.025-1.040 vs. 1.043, 95%CI= 1.036-1.049). The result also shows variations in the odds of death by land use categories, but this wasn’t statistically significant; the highest odds of death were in ports and airport areas (1.149, 0.959-1.376), and the lowest was in forested and agricultural land (0.986, 0.848-1.146)	Moderate
Petrou et al. (2015). Yorkshire and the Humber, West Midlands, North East, North West and South East regions	Secondary data analysis	Study to identify possible acute heat-induced summer mortality in five regions of England and reveal associations with specific airflow	Daily maximum temperature (DMAXT) and daily mean temperature (DMT) data referring to one representative county of each region ere provided in Celsius degrees (°C) by the ONS	A statistically significant 95% confidence interval increase in daily total mortality (DTMORT) was observed during the selected episodes in all five regions and thus, heat-induced mortality was indicated. Findings showed that in the Yorkshire and the Humber region, a 6.19% (95% CI = 3.65, 8.73%) increase in DTMORT was detected during the selected days. An 11.3% (95% CΙ = 8.7, 13.9%) rise in DTMORT was computed in the West Midlands region during the selected days. DTMORT in the North East region was increased by 4.7% (95% CI = 1.6, 7.9%) during the selected days. In the North West region, a 13.1% (95% CI = 10.8, 15.4%) increase in DTMORT was associated with high-temperature episodes. An 11.9% (95% CI = 10.1, 13.6%) increase in DTMORT corresponded to the selected days in the South East region	Moderate
Zhang et al. (2018) England and Wales	Secondary data analysis - time series (14 years)	Study to provide national estimates for DTR-associated effects on mortality and explore whether season and regional-level characteristics modify DTR-mortality relation in the United Kingdom.	The DTR-mortality association was investigated with a two-stage analytic approach using the 14-year time-series data from the 10 regions in England and Wales.	A total of 7,573,716 persons died in England and Wales between 1993 and 2006, with a daily average of 148.1 deaths per region (ranging from 79.8 in the North East to 221.5 in the South East). The annual average temperature and relative humidity were 10.4°C (range: 9.5-11.7°C) and 74.7% (range: 67.4-78.3%), respectively. Daily DTR varied greatly from 0.8°C to 20.2°C with an annual average of 7.3°C for the included regions. DTR extremes (both high and low DTR) exhibited a significant impact on mortality. Clear evidence of increased mortality associated with extremely high DTR was revealed for all regions except North East, whereas extremely low DTR tended to show some protective effects. RR displayed as images	Moderate
Kim et al. (2019). 132 study sites across 12 countries including the UK.	Secondary data analysis	A multicounty study to investigate the associations between suicide and high ambient temperature.	Daily data on weather conditions were obtained for 306 communities from 12 countries/regions. Weather data included daily minimum, mean and maximum temperatures, and relative humidity.	Mean summer temperature for the 10 UK locations= 15.6 (14.5-17.2). Suicide rate per 100,000= 6.9. The minimum suicide temperature (°C) (MinST) and maximum suicide temperature (°C) (MaxST) were −0.7 (1%ile) and 20.7 (99th percentile). The mean RR for suicide and temperature = 1.34 (1.22, 1.46)	Moderate
Gasparrini et al. (2015a p. 272) locations in Australia, Canada, South Korea, Spain and the UK	Secondary data analysis	Study to assess the temporal variation in heat-mortality associations in a multi-country data set using flexible modelling techniques.	The exposure index was chosen as mean daily temperature, computed as the 24-hr average. The data were restricted to the summer period, identified as the four warmest months of the year using average monthly temperatures. These months consistently correspond to the period December–March in Australia and to June–September in the other countries	Time-series daily weather data were collected from 272 locations in seven countries. Findings showed no statistically significant finding was observed for the UK	Moderate
Gasparrini et al. (2015b)	Secondary data analysis	Study to quantify the total mortality burden attributable to either heat or cold across 13 countries.	The exposure index was defined as daily temperature a calculated from central monitor stations, either as the average between maximum and minimum values or the 24 h average across 84 locations in 13 countries	The minimum mortality percentile in the UK is the 90th percentile. Total deaths due to heat=0.3% (0.25%-0.36%)	Moderate
de Schrijver et al. (2021). UK and Switzerland	Secondary data analysis	Study to critically assess the differences in temperature-related mortality risks and impacts derived from Gridded Climate Datasets GCDs of variable characteristics and weather stations across two heterogeneous regions	Mean daily temperature data from three different types of sources or exposure datasets: (1) weather station data, often used as the gold standard in environmental epidemiology, (2) local high-resolution GCDs, and (3) global GCD with coarser resolution were used	Excess deaths from heat in England and Wales= 2,979 (2,419, 3,493), 2,943 (2,404, 3,465), and 2,906 (2,425, 3,401) for the weather station and local and global GCD, respectively RR estimates for heat in Greater London were 1.25 (95% CI; 1.19-1.30), 1.24 (95% CI; 1.18-1.29), and 1.26 (95% CI; 1.20-1.33) for the weather station and local and global GCD, respectively.	Moderate
Heaviside et al. (2016). West-Midlands	Secondary data analysis plus modelling	Study to investigate the attribution of the UHI to heat-related mortality in the West Midlands during the heatwave of August 2003 by comparing health impacts based on two modelled temperature simulations.	Modelled, gridded air temperature at a horizontal resolution of 1 km x 1 km and a height of 2 m, covering an area of ~6,300 m2 within the West Midlands region was used. To investigate the effect that urban surfaces have on local temperature, and the associated health impacts, 2 different WRF (Weather Research Forecasting) model simulations were compared	The results suggest that the UHI contributed around 50% of the total heat-related mortality during the 2003 heatwave in the West Midlands. Following the HIA method, the estimated number of deaths during the 10 day heatwave period for the West Midlands was approximately 90, based on the population-weighted daily mean simulated temperature for Birmingham and the West Midlands, which includes the UHI effects. The HIA for the ‘rural’ simulation over the same heatwave period gives estimated mortality of 43. UHI effect could be accountable for around 52% of the total heat-related mortality in the West Midlands during the 2003 heatwave.	Moderate
Evangelopoulos et al. (2021). London	Secondary data- time series	Study to provide quantitative estimates of the effects of temperature increases on the risk of mortality by the climatic zone of the country of origin for people born outside the UK and compare the effects with those born in the UK.	climatic zone of birth was classified into five categories- UK, Tropical, Boreal, including countries with sub-polar or continental temperate climate, Sub-tropical including countries with arid-hot or Mediterranean climate and Mixed, including countries with varying climate within their borders. Meteorological data consisted of 24-hour averages of air temperature (oC), relative humidity (%) and wind speed (m/s) as measured from central monitoring stations	The total number of deaths analysed for the warm season (April to September) of the years 2004-2013 was 200,180 and 158,356 for all ages and those >65 years old respectively. The relationship between mean temperature and all-cause mortality was non-linear but of different shape and with varying minimum mortality temperature for each of the five climatic zone groups (UK, tropical, boreal, sub-tropical and mixed regions) The minimum mortality temperature (MMT) was 16.9 degrees. An increase from MMT to 21C resulted in an 8% increase in the risk of death for persons born in the UK 1.08 (95% CI=1.05-1.10). 25C Vs MMT1.26 (1.18-1.35) For those born in tropical regions, 21C Vs MMT=1.07 (1.01-1.13) and 25C Vs MMT= 1.35 (1.08-1.69) For those born in Boreal regions, 21C Vs MMT= 1.10 (1.03-1.16) and 25C Vs MMT=1.39 (1.13-1.71) For those born in sub-tropical regions, MMT was >25C For those born in mixed regions 21C Vs MMT= 1.14 (1.01-1.29) and 25C Vs MMT=1.12 (0.86-1.46) Findings suggest that UK, tropical and boreal climate born people have an increased risk of death from heat and migrants show little adaptation to their new climate zone	Moderate

Table 3. Main findings from studies on extreme heat and emergency hospital admission.

Study, location	Study design	Aim(s)	Exposure	Main findings	Quality of study
Kovats et al. (2004)/London	Secondary data analysis- Time-series	Study to examine the effects of hot weather and heatwaves on emergency hospital admissions in Greater London.	Daily meteorological data (minimum and maximum temperature and relative humidity) were provided by the MET office using data for Heathrow meteorological station Daily mean temperature value was created by getting an average of the daily minimum and maximum value	Data on emergency hospital admission were obtained from the hospital episode statistics. Daily admissions were stratified into eight age groups and six diagnostic groups- cardiovascular disease, respiratory disease, cerebrovascular disease, renal disease, acute renal failure and calculus of the kidney and ureter. The mean of daily emergency admission during the study period of 6 years for all causes =2644.5. 5th percentile=1639, 95th percentile=3464. The mean temperature for the study period=11.6C. 5th centile=3.1, 95th centile=26.7. Ozone ppb mean=17.7, 5th centile=3, 95th centile=33. PM10 mean =26.0, 5th centile=13, 9th centile=50. Relative humidity % mean=75.2, 5th centile=52.8. 95th centile =90.6. Findings for most of the age groups were not statistically significant. However, in those aged 75 years and above, respiratory admissions increased by 10.86% (95%CI=4.44 to 17.67) for each degree rise in daily mean temperature above 23 degrees An increase in daily mean temperature above 12°C was associated with increased emergency hospital admissions (0.24% 95%CI=0.02%-0.46%) in infants and children under 5 years.	Moderate

Table 4. Main findings from studies on extreme heat and YLL.

Study, location	Study design	Aim(s)	Exposure	Main findings	Quality of study
Arbuthnott et al. (2020) Greater London, the West Midlands and Greater Manchester	Secondary data analysis- ecological time series regression analysis	Study to (a) to determine the nature of the relationship between YLL and temperature in the studied conurbations, (b) to estimate (and compare) the proportion of total yearly mortality and YLL attributable to heat and cold	Daily mean temperature obtained from the UK Met Office UKCP09 gridded observation datasets	Findings show that in London, each 1°C above the heat threshold the YLL increased by 3.0% (2.5%, 3.5%). Greater Manchester YLL= 1.5% (1.07-2.4%). West Midlands 2.4% (1.6-3.3%). Between 1996 and 2013, the proportion of YLL attributable to heat in London was 0.40%. The percentage of year-round YLL attributable to heat was 0.391% for Greater London, 0.309% in the West Midlands and 0.206% in Greater Manchester	Strong

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Murage, P., et al., 2020. What individual and neighbourhood-level factors increase the risk of heat-related mortality? A case-crossover study of over 185,000 deaths in London using high-resolution climate datasets. Environment international, 134, 105292. doi:10.1016/j.envint.2019.105292

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Evangelopoulos, D., et al., 2021. Does climatic zone of birth modify the temperature-mortality association of London inhabitants during the warm season? A time-series analysis for 2004–2013. Environmental research, 193, 110357.

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Kovats, R.S., Hajat, S., and Wilkinson, P., 2004. Contrasting patterns of mortality and hospital admissions during hot weather and heat waves in Greater London, UK. Occupational and environmental medicine, 61 (11), 893–898. doi:10.1136/oem.2003.012047.

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