Heat and health of occupational workers: a short summary of literature

Abstract Globally, occupational workers suffer various health impacts due to extreme heat. In this short review, we examine the literature discussing health impacts of heat on occupational workers, and then discuss certain individual and institutional measures needed to address the problem. Though the available literature in the recent decade discusses health impacts of heat on workers as various heat-related illnesses, we found very few studies examining how occupational workers suffer from issues concerning cardiovascular health, neurological health, respiratory health, and mental health. In this regard, we highlight the need for more studies to examine how occupational workers exposed to extreme heat conditions suffer from fatal health issues like cardiovascular attack, brain stroke, and other ailments impacting vital organs of the body. Occupational workers across the world should be made aware of measures to protect themselves from extreme heat. Further, countries should develop occupational heat safety guidelines with statutory effect.


Introduction
Occupational workers are categorized as one of the most atrisk groups threatened by heatwaves.The potential consequences of occupational heat stress on workers, workplaces, and global economies in the context of climate change are substantial. 1The impact of heat exposure can be particularly harsh on outdoor workers such as those engaged in agriculture, construction, mining, manufacturing sectors, and also on armed forces personnel and firefighters. 2Therefore, it is important to address the burden of heat on workers because global projected increases in mean temperatures and heatwaves may aggravate the risk of adverse heat health effects and exacerbate disparities. 3Against the backdrop of existing research on the occupational heat-health problem, our study highlights that studies of extreme heat impacts on workers must consider not just heat-related illnesses but also long-term health consequences impacting cardiovascular health, neurological health, respiratory health, and mental health.Our study also suggests certain individual and institutional reforms to protect workers from heat-related illnesses and long-term health consequences.

Materials and methods
For this Opinion summary, we used the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) approach to systematically search literature in the PubMed database.We used "occupational heat exposure" as a key search term to identify the literature.

Inclusion and exclusion criteria
First, we included peer-reviewed publications written in English that examined the health impacts of heatwaves in occupational workers.Second, we included publications that discussed evidence-based suggestions, strategies, and measures to address the occupational heat-health problem.As we were interested in the more recent evidence, we included only papers published between January 1, 2012 and December 31, 2022.We excluded review articles and commentaries for this study.The schematic of the search strategy is shown in Figure 1.The full list of studies obtained and excluded at various stages is given in Appendix S1 along with author names and DOIs/links.

Results
We categorized the evidence as per inclusion criteria into 2 groups: (1) literature that discussed the effects of heatwaves on occupational workers and how occupational heat exposure is a problem for workers from available evidence; and (2) literature on evidence-based suggestions, strategies, and measures to address the occupational heat-health problem.

Heat as a health hazard for workers: summarizing global evidence
Thirty-five studies from across the world discussed heat as a health hazard for workers in various settings.Table 1 summarizes the evidence for informal occupational workers who do not have access to labour protections or social protection including construction workers, those engaged in mining activities, agricultural workers, and other industrial laborers, and also for professional workers.

Interventions to address occupational heat-health threats
One study highlights the need to develop more effective prevention programs to reduce worker heat-related morbidity and mortality. 40Findings at a construction site in Japan indicated that heat effects on workers can be addressed by strategies that include cool drinking water availability, personal monitoring of heart rate or body water loss, providing recovery areas, voluntary breaks for workers, and providing health education for workers on heat stroke prevention strategies. 41Two studies discussed a "water, rest, shade" intervention to reduce the impact of heat stress on the health of sugarcane farmers. 42,43Two studies highlighted the importance of heat-related training programs, 7,44 of which one called for updating existing workplace heat prevention policies, targeted and mandatory high-temperature regulations, and concerted efforts from all stakeholders. 7One study called for strict adherence to a heat stress management program to minimize heat stress and strain among the workers, 21 and another highlighted preventive measures such as engineering controls and heat acclimatization programs. 29ome studies have highlighted how hydration can impact the health of workers.One study highlighted the need to correct poor hydration practices like irregular drinking patterns and nonplain f luid intake among outdoor workers as these are found to impact the severity of heat-related illnesses. 45Another study found that traditional low-cost dietary methods like consumption of buttermilk have potential to mitigate occupational heat strain by cooling the body, lowering sweat rate, improving hydration, and reducing hormonal stress. 46As the risk of raised blood pressure increases among heat-exposed workers due to nutrient losses, there may be a need to increase dietary intakes of vitamin C, potassium, and calcium. 19A study in Guatemala found that hydration could be protective to address the risk of acute kidney injury among agricultural workers exposed to heat stress. 47ccording to a study in India, female brick workers adopted a strategy of reduced walking speed to cope with physiological strain caused by extreme heat exposure. 48A multicountry study highlighted the need for a focus on work-rest cycles and ventilated clothing to mitigate the physiological heat strain experienced by workers. 49Heat monitoring at workplaces in hot tropical countries, providing shade for outdoor workers, reduction in work intensity, heat protection advice for workers in local languages, and access to clean drinking water are important to reduce occupational heat stress. 50One study highlighted the importance of mobile technology to provide heat safety education for farm workers, 51 and 2 studies discussed the development of heat-health warning systems in the occupational context for the protection of workers. 52,53scussion and future direction Whereas most of the available evidence discussed the health impacts of heat exposure on workers as heat-related illnesses including headaches, dizziness, and fainting, only 5 studies 10,11,18,22,30 discussed heat-related health disorders such as kidney disorders in workers.There is little evidence regarding the impacts of heatwaves on cardiovascular health, neurological health, respiratory health, or mental health of workers.Though there are studies that have attributed heatwaves as a major predisposing factor triggering heart, brain, lung, and mental health illnesses for the general public, we find limited evidence in the context of occupational workers.To establish extreme heat as a major risk factor for occupational workers, we need more evidence-based studies to discuss impacts on cardiological health, neurological health, respiratory health, and mental health for occupational workers.Our study suggests that research in the context of heatwaves and occupational workers must focus more on heat-related health disorders over heat-related illnesses.
Next, we highlight individual strategies to address the impact of heatwaves on workers (Figure 2).Among the individual protective strategies for workers, consumption of clean drinking water, regular hydration, accessing shade, resting whenever uncomfortable, and self-reporting of heat-related illness symptoms are predominantly emphasized.As described by a study on the benefits of traditional drinks like buttermilk that can provide a cooling effect, popularizing the consumption of local traditional drinks that have an effective hydration and cooling effect could be beneficial for workers.
As the health impacts of heatwaves on occupational workers working outdoors continue to worsen globally, there is a need for institutional measures by developing statutory and legislative provisions to address the challenge.Some countries in West Asia have incorporated mandatory work bans as a part of "workplace safety and health guidelines" when temperatures breach certain maximum thresholds.For example, Qatar's rules on workers prohibit work in outdoor workspaces from 11:30 am to 3:00 pm, between June 15 and August 31, and regardless of the time, all work must stop if the wet-bulb globe temperature (WBGT) rises beyond 32.1 • C in a particular workplace 54 ; Saudi Arabia and UAE enforce a 3-month ban on working under the sun between noon  10 Thailand Kidney disease among workers Crowe et al (2022) 11 Costa Rica Kidney injury and aggravating the risk of chronic kidney disease among agricultural workers Venugopal et al (2019) 12 India Inhibiting DNA repair systems and damaging the DNA among industrial workers Venugopal et al ( 2016) 13 India Heat-related illnesses and urogenital symptoms Xiang et al (2016) 14 South Australia Heat-related illnesses Sadiq et al (2019) 15 Nigeria Heavy sweating, tiredness, dizziness, and headaches among agricultural workers Fortune et al (2013) 16 Ontario, Canada Increased concentration of heat-related illnesses Wagoner et al (2020) 17 North Mexico Increased incidence of dehydration among agricultural workers Wesseling et al (2016) 18 Nicaragua Greater risk of heat stress, dehydration, and poor renal function among sugarcane workers while construction workers and subsistence farmers also face the risk Tang et al (2016) 19 China Increased blood pressure among heat-exposed steel workers due to vitamin C, potassium, and calcium losses Sahu et al (2013) 20 India Lower heart rate recovery due to heat exposure indicating cardiovascular strain among the rice harvesters Dang et al (2014) 21 Texas, United States Increase in postshift blood bicarbonate, blood urea nitrogen, creatinine, and urine specific gravity among the workers at an aluminum smelter Moyce et al (2017) 22 California, United States Acute kidney injury and heat strain symptoms among agricultural workers Petitti et al (2013) 23 Maricopa County, Arizona, United States Heat-associated deaths among those associated with construction/extraction and agriculture activity Dally et al (2020) 24 Southwest Guatemala Average daily wet-bulb globe temperature >30 • C increased risk of occupational injuries and dehydration among agricultural workers Spencer et al (2022) 25 Gambia Headache, dizziness, nausea, and chills among pregnant women farmers Pradhan et al (2019) 26 Qatar Increased cardiovascular mortality among Nepali migrant workers based in Qatar Wang et al (2022) 27 China Exposure to occupational heat stress is associated with carotid atherosclerosis among male steelworkers Habib et al (2021) 28 Lebanon At least 1 of heat stress-related health symptoms (fainting or dizziness, nausea, weakness, confusion, muscle cramps, hot dry skin, and chills) among bakery workers Seng et al (2018) 29 Singapore Heat stress symptoms among workers in rice vermicelli manufacturing factories Dally et al (2018) 30 Guatemala Evidence for the link between impaired kidney function, increased heat exposure, and agricultural worker productivity Riccò et al (2020) 31 Northern Italy Increased daily rates of occupational injuries in agricultural workers from northern Italy Hinchliffe et al (2023) 32 Spain No evidence for an association between heat exposure and colorectal cancer risk Hinchliffe et al (2023) 33 Canada, France, and Spain No evidence for an association between heat exposure and prostate cancer risk Raval et al (2018) 34 Ahmedabad, India Heavy sweating, intense thirst, dry mouth, loss of work capacity, loss of coordination, breathlessness, chest pain, loss of appetite, red eyes, headache, and stomach acidity among traffic police Watkins et al (2021) 35 United Kingdom Increased cytokine levels suggestive of systemic inf lammation with a risk of cardiac events among fire service instructors Al-Otaibi et al (2022) 36 Al-Khobar, Saudi Arabia Increased heart rate, respiratory rate, and core body temperature and biochemical changes among bakers Al-Otaibi et al (2022) 37 Al-Khobar, Saudi Arabia Abnormal hematological parameters-high hemoglobin and low platelet values among bakers Zhou et al (2014) 38 Jinan, China Physiological and psychological health impacts on bus drivers Erickson et al (2019) 39 United States Higher prevalence of heat-related symptoms among disaster responders and 3:00 pm, 55,56 and Bahrain enforces a ban for 2 months. 57We suggest other countries could also adopt measures such as work bans during extreme heat conditions.When deaths occur among the workers, there must be reforms to update death records to highlight the cause of mortality as heat exposure. 26urther, occupational heat safety guidelines of all countries globally must contain provisions to provide cooling appliances to bring temperatures down at work places.There must also be mandatory checks on measures to ensure adequate ventilation and maintain ambient temperatures at work places during heatwave conditions.The guidelines also highlight the importance of "work appropriate clothing" like the use of light cotton clothing in hot working conditions.It is also important to recognize heat stroke as an industrial accident to ensure that affected workers are eligible for compensation.In the future, it is also important for countries to study occupational heat safety guidelines and legislation of countries that adopt best practices and have shown positive results in addressing the problems of occupational workers during heatwaves.

Figure 1 .
Figure 1.PRISMA f lowchart of studies included in the summary review.

Figure 2 .
Figure 2. Strategies to address heat impacts on the health of workers.

Table 1 .
Evidence of workers reporting heat-health problems.