Clues Found in Nicaraguan Sugar Cane Worker Kidney Disease Epidemic

photo of sugar cane workers cutting sugar caneNew York, NY – The epidemic of kidney disease among young Central American agricultural workers may be the result heat stress and volume depletion, according to new research published today in the National Kidney Foundation's American Journal of Kidney Diseases.

In Nicaragua and El Salvador, age-adjusted mortality rates from kidney disease are among the highest in the world. According to researchers, in these countries, the prevalence of kidney disease (defined as eGFR<60 mL/min/1.73m2) in affected communities is 12%-18% in the general population and 14%-26% in men with age-specific rates among younger men up to 15 times higher than in the United States.

“It’s a public health emergency, but we still don’t fully understand why this is happening,” said Rebecca Laws, PhD, a Postdoctoral Associate at Boston University School of Public Health and lead author on the study. “Most researchers believe the causes are multifactorial, and it is at least in part related to occupation, given the severe toll that kidney disease is taking on heavy manual laborers in the region.”

For the study, researchers followed 284 sugarcane workers in seven different jobs from one company in northwestern Nicaragua. Blood and urine samples were collected from participants before and near the end of the six-month harvest season. Those workers who had the most labor-intensive jobs, cane cutters, had increased urinary NGAL and IL-18, both biomarkers of kidney injury.

“These individuals have the most physically strenuous jobs in a high-heat setting,” said Dr. Laws. “They are also being paid by the amount they cut. It’s a system that can increase physical strain.”

While self-reported hydration didn’t seem to offer any protective benefit to sugarcane workers overall, when stratified by job, researchers observed a protective effect of consuming an electrolyte solution among cane cutters and seed cutters. This indicates there are ways to prevent kidney injury among laborers in high-heat settings. 

“At this point we don’t know for certain that heat stress and volume depletion are causal, but we can say that electrolyte supplementation appears to reduce risks of kidney damage in occupations that expose workers to heat stress and volume depletion,” said Dr. Laws.

“This study will hopefully promote more research on whether hydration status has a significant impact on progression of kidney disease,” said Thomas Manley, director of scientific activities for the National Kidney Foundation. “Studies on the benefit of water intake for those with kidney disease have been mixed.  It certainly seems intuitive that persistent physical stress and dehydration could negatively impact kidney function, but further work on the relationship of hydration and kidney disease is needed.”

The authors note there are some limitations to this study, as they didn’t directly measure heat or exposure to chemicals. Job category was used a surrogate for exposure. There is also the possibility of environmental and genetic factors at play. These are all avenues of inquiry that will be studied by Dr. Laws and her team in the future.

“We’re planning a longitudinal study in Nicaragua and El Salvador in sugarcane and other industries to further investigate kidney disease in this region,” Dr. Laws said. “We are also doing a cross sectional study in adolescents and children to find other potential sources of kidney damage in this population.”

This research was partially funded by the Comité Nacional de Productores de Azúcar (CNPA) and the World Bank. Funders did not have the opportunity to review or influence the content of the paper prior to publication.

The National Kidney Foundation is the leading organization in the U.S. dedicated to the awareness, prevention and treatment of kidney disease. For more information, visit www.kidney.org.