Increasing global temperatures and water shortages are two of the biggest climate change challenges facing the world, but the potentially deadly impacts of extreme heat on human health are already being felt in parts of the world.

How can we protect the health of people working in extreme temperatures?

Sugarcane workers in Central America are suffering from excessive heat exposure and, over the last 30 years, tens of thousands of them have died prematurely from chronic kidney disease of undetermined cause (CKDu) - a disease linked to excessive heat exposure and dehydration suffered at work.

With the worst cases occurring in Nicaragua, the phenomenon is seen across Central America, as workers in El Salvador, Costa Rica and Mexico fall prey to this insidious killer that strike hardest at those toiling in the fields under a blazing sun. The condition hits workers in the sugarcane industry particularly hard, with no treatment available once it has taken hold and limited healthcare facilities available in many of the affected countries.

“We don’t know what’s causing the condition to strike so many sugarcane workers; it’s not associated with toxins or pesticides and is clustered in lowland regions where temperatures are higher and work is very strenuous,” comments Dr Rebekah Lucas, Lecturer in Physical Activity and Health in the University of Birmingham’s School of Sport, Exercise & Rehabilitation Sciences (SportEx).

“The condition is so prevalent in ex-sugarcane workers that there is a clear link to this line of agricultural work. Cutting cane has the highest rates of pay, but workers push themselves beyond safe limits. Some companies screen their employees for health conditions, but this can push workers into less regulated areas of work.”

Dr Lucas is a member of the international team of scientists responding to this terrible condition. The Adelante Initiative is taking place at Ingenio San Antonio (ISA), a large sugarcane mill in Nicaragua, where an expert team has spent the last three years studying a cohort of 700 workers. The research team is studying how access to water and rest in shade, together with better equipment, might improve work conditions and prevent CKDu among workers while preserving their productivity.

The scientists started in with 2017 with a preliminary assessment of cross-harvest changes in biomarkers for cane cutters, seed cutters, irrigation workers and others, before developing a pilot intervention program for cane and seed cutters. They also designed interventions for other industries and worked with industry regulators to incorporate the project’s learnings into certifications and industry standards.

“I’m proud to work on the Adelante Initiative, which is making a real difference to protecting the health of workers in an agricultural sector whose employees are particularly affected by soaring temperatures,” comments Dr Lucas. “CKDu takes time to progress and during the time we have been working with our cohort of workers, we have seen a consistent decline in kidney injuries after our interventions have been put in place.

“The project’s success has been achieved through looking at health and safety practice at ISA through the lens of workers’ health. We’ve been able to change behaviours by talking to workers and showing them that they wouldn’t lose productivity – and wages – by adopting safer working practices.”

The project is funded through La Isla Network, a Non-Governmental Organisation dedicated to ending CKDu among workers and their communities worldwide. Workplace safety interventions and policy change drawn from the Adelante Initiative have enabled the project team to develop toolkits that can be used to protect other workers at risk from the condition – not just in Central America, but around the world in places like Sri Lanka.

“We’re hoping to be able to secure additional funding that will allow us to further investigate heat and dehydration as causal factors in CDKu,” adds Dr Lucas. “We want to see an end to this disease; raising awareness of the condition whilst improving workplace standards for people across the Global South.”

Dr Lucas is also a key team member on a different SportEx research project working with the US Army exploring the impact of high temperatures on the body’s ability to effectively use carbohydrates in food during prolonged and strenuous exercise.

During such exercise, the body relies on carbohydrate fuel stores located in muscle and liver to support energy production and allow the muscles to keep working. These carbohydrate stores are small and when depleted, fatigue can occur.

Many sportspeople eat or drink carbohydrate-containing foods or drinks during exercise to provide an additional source of energy and delay the onset of fatigue. When exercise is performed in hot conditions, the body’s capacity to use carbohydrate fed during exercise for energy – known as exogenous carbohydrate oxidation - appears to be reduced.

Led by Dr Gareth Wallis, Associate Professor in Exercise Metabolism, the three-year project sees SportEx researchers working with the US Army Research Institute of Environmental Medicine (USARIEM) to develop nutrition strategies to combat this drop in effective conversion of carbohydrates during the body’s exposure to extreme environments.

This is a particular problem for military personnel deployed in areas of extreme temperature, as the heat places even more demands on the body’s existing carbohydrate reserves – making the capacity to use carbohydrate fed during exercise even more important.

“Heat impairs the body’s ability to use carbohydrates – whether they come from ration packs, performance drinks or energy bars; ironically, these are often the moments when fatigue is setting in and the need for an energy boost from carbohydrates is greatest,” explains Dr Wallis.

“Our research will explore the physiological mechanisms behind this. One hypothesis that we will be testing is that the body’s ability to absorb carbohydrates is linked to blood flow in the intestine. Extreme temperatures prompting movement of blood away from this part of the body to cool the skin could account for reduced energy drawn from consumed carbohydrates.”

The research team will also explore the benefits of heat acclimatisation techniques on how the body assimilates carbohydrates in high temperatures. Using SportEx acclimatisation chambers on the Birmingham campus, a volunteer cohort of around 20 amateur athletes will undergo a nine-day heat acclimatisation programme.

Testing will run over two-and-a-half years with heat acclimatisation taking place in winter and spring in order to give the most accurate measure of its impact. Heat, humidity and oxygenation can be varied in the chambers, as researchers measure breath, blood, muscle samples and more to pull together a comprehensive physiological profile of the athletes’ progress.

“We’re looking forward to tackling the research challenge that lies ahead, as the findings of our research could have implications for people in occupations that can require strenuous physical effort in hot conditions such as military personnel, firefighters and athletes,” comments Dr Wallis.

“Indeed, it’s not inconceivable that our research could one day provide further help to vulnerable workers such as the sugarcane cutters of Central America in maintaining their productivity whilst protecting their health.”


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