High ambient working temperatures cause physiological damage to the human body
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Peer-reviewed systematic reviews and meta-analyses establish that high ambient working temperatures and occupational heat strain pose direct threats to worker health, increasing morbidity, mortality, and disease incidence.
<h4>Background</h4>Occupational heat strain (ie, the effect of environmental heat stress on the body) directly threatens workers' ability to live healthy and productive lives. We estimated the effects of occupational heat strain on workers' health and productivity outcomes.<h4>Methods</h4>Following PRISMA guidelines for this systematic review and meta-analysis, we searched PubMed and Embase from database inception to Feb 5, 2018, for relevant studies in any labour environment and at any level of occupational heat strain. No restrictions on language, workers' health status, or study design were applied. Occupational heat strain was defined using international health and safety guidelines and standards. We excluded studies that calculated effects using simulations or statistical models instead of actual measurements, and any grey literature. Risk of bias, data extraction, and sensitivity analysis were performed by two independent investigators. Six random-effects meta-analyses estimated the prevalence of occupational heat strain, kidney disease or acute kidney injury, productivity loss, core temperature, change in urine specific gravity, and odds of occupational heat strain occurring during or at the end of a work shift in heat stress conditions. The review protocol is available on PROSPERO, registration number CRD42017083271.<h4>Findings</h4>Of 958 reports identified through our systematic search, 111 studies done in 30 countries, including 447 million workers from more than 40 different occupations, were eligible for analysis. Our meta-analyses showed that individuals working a single work shift under heat stress (defined as wet-bulb globe temperature beyond 22·0 or 24·8°C depending on work intensity) were 4·01 times (95% CI 2·45-6·58; nine studies with 11 582 workers) more likely to experience occupational heat strain than an individual working in thermoneutral conditions, while their core temperature was increased by 0·7°C (0·4-1·0; 17 studies with 1090 workers) and their urine specific gravity was increased by 14·5% (0·0031, 0·0014-0·0048; 14 studies with 691 workers). During or at the end of a work shift under heat stress, 35% (31-39; 33 studies with 13 088 workers) of workers experienced occupational heat strain, while 30% (21-39; 11 studies with 8076 workers) reported productivity losses. Finally, 15% (11-19; ten studies with 21 721 workers) of individuals who typically or frequently worked under heat stress (minimum of 6 h per day, 5 days per week, for 2 months of the year) experienced kidney disease or acute kidney injury. Overall, this analysis include a variety of populations, exposures, and occupations to comply with a wider adoption of evidence synthesis, but resulted in large heterogeneity in our meta-analyses. Grading of Recommendations, Assessment, Development and Evaluation analysis revealed moderate confidence for most results and very low confidence in two cases (average core temperature and change in urine specific gravity) due to studies being funded by industry.<h4>Interpretation</h4>Occupational heat strain has important health and productivity outcomes and should be recognised as a public health problem. Concerted international action is needed to mitigate its effects in light of climate change and the anticipated rise in heat stress.<h4>Funding</h4>EU Horizon 2020 research and innovation programme.
<h4>Background</h4>Sub-Saharan Africa (SSA) contributes very little to overall climate change and yet it is estimated to bear the highest burden of climate change, with 34% of the global DALYs attributable to the effects of climate change found in SSA. With the exception of vector-borne diseases, particularly malaria, there is very limited research on human health effects of climate change in SSA, in spite of growing awareness of the region's vulnerability to climate change.<h4>Objectives</h4>Our objective is to systematically review all studies investigating temperature variability and non-vector borne morbidity and mortality in SSA to establish the state and quality of available evidence, identify gaps in knowledge, and propose future research priorities.<h4>Methods</h4>PubMed, Ovid Medline and Scopus were searched from their inception to the end of December 2014. We modified the GRADE guidelines to rate the quality of the body of evidence.<h4>Results</h4>Of 6745 studies screened, 23 studies satisfied the inclusion criteria. Moderate evidence exists to associate temperature variability with cholera outbreaks, cardiovascular disease hospitalization and deaths, and all-cause deaths in the region. The quality of evidence on child undernutrition is low, and for diarrhea occurrence, meningitis, Ebola, asthma and respiratory diseases, and skin diseases, very low.<h4>Conclusions</h4>The evidence base is somehow weakened by the limited number of studies uncovered, methodological limitations of the studies, and notable inconsistencies in the study findings. Further research with robust study designs and standardized analytical methods is thus needed to produce more credible evidence base to inform climate change preparedness plans and public health policies for improved adaptive capacity in SSA. Investment in meteorological services, and strengthening of health information systems is also required to guarantee timely, up-to-date and reliable data.
Temperature extremes vary across Africa. A continent-wide examination of the impacts of heat on health in Africa, and a synthesis of Africa-informed evidence is, however, lacking. A systematic review of articles published in peer-reviewed journals between January 1992 and April 2019 was conducted. To be eligible, articles had to be Africa-specific, in English, and focused on how heatwaves and high ambient temperatures affect morbidity and mortality. A secondary systematic analysis on policies and interventions comprising 17 studies was also conducted, and the findings synthesised together with those of the 20 primary studies. Eleven studies showed that high ambient temperatures and heat waves are linked with increased mortality rates in Africa. These linkages are characterised by complex, linear and non-linear (J or U) relationships. Eight of the nine primary studies of morbidity outcome reported that an increase in temperature was accompanied by raised disease incidence. Children and the elderly were the population groups most vulnerable to extreme heat exposure. Location-specific interventions and policy suggestions include developing early warning systems, creating heat-health plans, changing housing conditions and implementing heat-health awareness campaigns. In summary, this review demonstrates that, while heat-health relationships in Africa are complex, extreme temperatures are associated with high mortality and morbidity, especially amongst vulnerable populations. As temperatures increase across Africa, there is an urgent need to develop heat-health plans and implement interventions. Future studies must document intervention effectiveness and quantify the costs of action and inaction on extreme heatrelated mortality and morbidity. Significance: Empirical evidence shows that the relationship between heat and human health is complex in the African This complexity has implications for the development of interventions and policies for heathealth on the continent. This review is important for African policymakers, practitioners and others who support Africa’s adaptation to climate change. Through this review, a compendium of Africa-specific and relevant empirical information is aggregated and made readily available to various interested and affected parties.
Occupational heat stress poses a major threat to worker health and safety that is projected to worsen with global climate warming. To manage these adverse effects, most industries rely on administrative controls (stay times and work-to-rest allocations) that are designed to limit the rise in body core temperature in the 'average' individual. However, due to the extensive inter- and intra-individual variation in thermoregulatory function, these administrative controls will result in some individuals having their work rate and productivity unnecessarily restricted (false positives), while others may be subject to rises in heat strain that compromise health (false negatives). Physiological monitoring has long been touted as a more effective approach for individualized protection from excessive heat stress. This has led to extensive interest in the use of wearable technology for heat stress management from both the scientific community and manufacturers of wearable devices, which has accelerated in the past decade. In this review, we evaluate the merits of the recent and emerging approaches to manage occupational heat strain with wearable physiological monitors. Against this background, we then describe the issues that we perceive to be unresolved regarding the use of wearable heat strain monitors and the research efforts needed to address those issues. Particular emphasis is directed to the efficacy of existing physiological indicators of heat strain, how to define upper limits for those indicators and the efforts required to rigorously validate emerging wearable heat strain monitoring devices.
Exercise performance and capacity are impaired in hot, compared to temperate, conditions. Heat adaptation (HA) is one intervention commonly adopted to reduce this impairment because it may induce beneficial exercise performance and physiological and perceptual adaptations. A number of investigations have been conducted on HA but, due to large methodological differences, the effectiveness of different HA regimens remain unclear. (1) To quantify the effect of different HA regimens on exercise performance and the physiological and perceptual responses to subsequent heat exposure. (2) To offer practical HA recommendations and suggestions for future HA research based upon a systematic and quantitative synthesis of the literature. PubMed was searched for original research articles published up to, and including, 16 February 2016 using appropriate first- and second-order search terms. English-language, peer-reviewed, full-text original articles using human participants were reviewed using the four-stage process identified in the PRISMA statement. Data for the following variables were obtained from the manuscripts by at least two of the authors: participant sex, maximal oxygen consumption and age; HA duration, frequency, modality, temperature and humidity; exercise performance and capacity; core and skin temperature; heart rate, stroke volume, cardiac output, skin blood flow, sweat onset temperature, body mass loss, sweat rate, perception of thirst, volitional fluid consumption, plasma volume changes; sweat concentrations of sodium, chloride and potassium; aldosterone, arginine vasopressin, heat shock proteins (Hsp), ratings of perceived exertion (RPE) and thermal sensation. Data were divided into three groups based upon the frequency of the HA regimen. Performance and capacity data were also divided into groups based upon the type of HA used. Hedges' g effect sizes and 95 % confidence intervals were calculated. Correlations were run where appropriate. Ninety-six articles were reviewed. The most common duration was 7-14 days and the most common method of HA was the controlled work-rate approach. HA had a moderately beneficial effect on exercise capacity and performance in the heat irrespective of regimen; however, longer regimens were more effective than shorter approaches. HA had a moderate-to-large beneficial effect on lowering core body temperature before and during exercise, maintaining cardiovascular stability, and improving heat-loss pathways. Data are limited but HA may reduce oxygen consumption during subsequent exercise, improve glycogen sparing, increase the power output at lactate threshold, reduce lactate concentrations during exercise, have a trivial effect on increasing extracellular concentrations of Hsp, and improve perceived ratings of exertion and thermal sensation. HA regimens lasting <14 days induce many beneficial physiological and perceptual adaptations to high ambient temperatures, and improve subsequent exercise performance and capacity in the heat; however, the extent of the adaptations is greatest when HA regimens lasting longer than 14 days are adopted. Large methodological differences in the HA literature mean that there is still uncertainty regarding the magnitude and time course of potential adaptation for a number of physiological and perceptual variables.
The effects of high ambient temperatures and heatwaves on health outcomes are well established, yet their impact on nutritional status remains poorly understood. This systematic review and meta-analysis aimed to synthesize current evidence on the association between elevated temperatures and anthropometric indicators in the general population. The protocol was registered in PROSPERO (CRD42024555573), and a systematic search of electronic databases was conducted in September 2025 using terms related to "high temperatures," "heatwaves," and "anthropometric indicators." Twenty studies were included, comprising 2,943,695 participants, predominantly children under five years of age, mainly from Sub-Saharan Africa. Studies demonstrated methodological heterogeneity, with mixed findings for height-for-age (HAZ) and weight-for-age (WAZ), but generally indicated an inverse relationship between high temperatures and anthropometric outcomes. In adults, elevated temperatures were associated with both underweight and obesity, highlighting complex effects on nutritional status. Meta-analyses in children revealed reductions of 0.12 SD in Weight-for-Height Z-scores and 0.03 SD in HAZ per 1°C increase in average temperature. While effect sizes at the individual level appear to be modest, the population-level implications could be considerable given the widespread and increasing exposure to heat. These findings suggest a potential link between thermal stress and nutritional status, underscoring the need for longitudinal and geographically diverse studies to further clarify causal pathways, identify vulnerable groups, and inform evidence-based climate-adaptive public health strategies aimed at mitigating the potential nutritional consequences of rising temperatures.
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