Sugar Cane Fields
© Jacopo Werther/Daniel Ramirez/Wikimedia Commons
Path between the sugar cane.
Does global warming cause kidney disease? According to a study published in the American Journal of Kidney Diseases, the root cause of a mystery illness which has killed 10s of thousands of sugar cane workers in Central America might be chronic dehydration, as a result of frequent hard, manual labour in extreme heat.

According to the study;
... Despite limited resources, we documented widespread decreased kidney function in coastal communities related to years of work on coastal sugarcane/cotton plantations. The high prevalence of eGFR <60 mL/min/1.73 m2 in the coastal communities, 18% of men aged 20-60 years, indicates the severity of the epidemic in a region where there is little to offer to patients and where CKD often progresses to ESRD and death. It is noteworthy that decreased eGFR also is related to cardiovascular morbidity and mortality. The risk of premature death from cardiovascular disease at CKD stages 3-4 is higher than that for reaching ESRD.38, 39 This study from El Salvador, as well as the recent Nicaraguan studies,23, 24, 25 provides important clues for etiologic studies, particularly heat stress.

It is urgent to assess the causes of this severe public health problem with properly designed etiologic and clinical research. A thorough medical workup including kidney biopsies and histopathologic examinations from a small group of affected individuals in rather early stages of CKD is needed to confirm the interstitial nature of the disease and provide clues with regard to pathogenesis. Etiologic research would use random samples from a proper study base and repeated measurements of all pertinent exposures with emphasis on heat exposure, environmental and water pollutants (particularly pesticide residues and heavy metals), and amount of water intake during work and rest.

Precautionary preventive actions must be implemented already at this stage, providing sufficient water and rest for workers in hot environments. There is a threat that global warming will dramatically increase populations exposed to hard work in hot climates. If heat stress is a causal factor for CKD, this disease will be an added health risk related to climate change.
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One of my first jobs was working in a poorly ventilated rubber and plastic moulding factory in Australia. During summertime, under the blazing Australian sun, the temperature outside frequently reached 104F (40c). Inside the factory the temperature often exceeded 120F (50c). Due to the poor ventilation, the air inside the factory was humid, and was thick with a haze of poisonous chemicals - sulphates, organo-chlorides, ketones, a thoroughly nasty cocktail of toxic substances. Undoubtedly anyone working in that environment sustained at least some organ damage, including most likely to our kidneys - we all absolutely stank of chemicals when the end of shift bell rang.

Why didn't we suffer high mortality rates, like the workers in this study?

For starters, we were properly hydrated - the one thing the company did right was to ensure we were receiving the correct amount of well balanced rehydration electrolytes, rather than whatever random concoction people working in third world cane fields receive. On the hottest days, someone would circulate with drinks every few minutes.

The other factor, is we were using machines. The work was boring, and physical, but it wasn't hugely strenuous. Nothing like the level of physical exertion required to work cane fields, without the benefits of modern technology.

If physical work in extreme heat is causing the mystery kidney disease, the simplest solution is surely to help workers in poor countries buy modern equipment, such as a few fossil fuel powered tractors and harvesters, to reduce the need for extreme manual exertion in harsh conditions.