Climate Change and Kidney Disease

Chronic kidney disease (CKD) is the fastest growing noncommunicable disease in the western world afflicting 1 in 7 adults (14%).  Climate and environmental changes are linked in most cases. Much of this is due to obesity related illnesses which the kidneys are a key target such as with Type 2 diabetes mellitus and hypertension. Increasing temperatures and pollution, especially with the inhalation of fine particulate matter (PM<2.5 µm), have been linked to obesity and other inflammatory associated conditions.

In 2002, a publication from El Salvador reported an abnormally high incidence of advanced CKD or end stage kidney disease (ESKD) in otherwise young, previously healthy sugarcane cutters without the traditional risk factors such as obesity, diabetes mellitus, hypertension, proteinuria, or widespread use of non-steroidal anti-inflammatory medications. After the initial publication follow up reports from Nicaragua, Costa Rica, and Guatemala reported similar findings in cane cutters.  

Initially named Mesoamerican Nephropathy, soon similar reports emerged from India, Sri Lanka, Thailand, Egypt, and Cameroon in other occupations such as rice workers, construction workers, salt workers, coconut harvesters, farmworkers, and miners. The unifying feature was long periods of intense labor in excessive temperatures with or without significant ambient humidity. This condition is now under the general term of chronic kidney disease of unknown cause (CKDu).

Initially agrochemicals such as organophosphates were suspected as a culprit. However, many studies and meta-analyses have failed to establish a link.  Risk factors include the number of harvests worked, hydration, silicate exposure, lower altitude (higher temperatures), length of workday, number of breaks, and payment by piece or volume versus hourly wage. Of note, sugarcane cutters in Brazil cut three to four times more cane per day than they did 25 years ago.

Three other factors have been implicated in the pathogenesis of this type of CKDu. They are as follow:

1. In the evenings prior to a sugar cane harvest the fields are burned to facilitate cutting, this exposes workers to silicates and fine particular matter (PM<2.5 µm) in addition to the work-related heat stress.  
2. Subclinical rhabdomyolysis with unresolved mild acute kidney injury add to previous kidney injury.  
3. The type of rehydration fluid, especially sugary fluids containing fructose, has also been implicated. Fructose is not metabolized in the same manner as glucose. Increased osmolarity and fructose activate the polyol pathway, ATP levels are reduced, uric acid is generated, leading to oxidative stress, hypoxia, and inflammation. The result is both glomerular injury and tubular injury, which if unchecked can lead to CKD and ESKD.

Measures that have demonstrated benefits have been implemented to reduce the risk of exposure to workers. They include frequent scheduled rest and shade breaks, access to appropriate electrolyte fluid replacement with low glucose concentrations, cooling centers, and rescheduling of the work hours, along with close monitoring and intervention for at-risk workers. Recent trials that have studied the addition of allopurinol to minimize kidney damage have also demonstrated a benefit.

Recently, several states have significantly weakened or banned heat-related worker education and reporting requirements as well as worker’s rest and hydration periods despite increasing heat risk. The public must be educated as to the short- and long-term risks along with the ethical implications of such shortsighted and dangerous measures.