Occupational heat stress and volume depletion may be contributing to an epidemic of chronic kidney disease (CKD) in Central America referred to as “Mesoamerican Nephropathy” that disproportionately affects young male agricultural workers, especially sugarcane cutters, according to a new report.
Investigators collected blood and urine specimens from 284 sugarcane workers at a company in northwestern Nicaragua before and near the end of the 6-month sugarcane harvest season. They looked at changes in levels of urinary kidney injury biomarkers normalized to urine creatinine level, including neutrophil gelatinase-associated lipocalin (NGAL), interleukin 18 (IL-18), N-acetyl bD-glucosaminidase (NAG), and albumin. They also calculated serum-creatinine-based estimated glomerular filtration rate (eGFR).
Field workers experienced increases in NGAL and IL-18 levels that were 1.49 and 1.61 times as high, respectively, as in non-field workers, Rebecca L. Laws, PhD, MPH, of the Boston University School of Public Health, and colleagues reported online ahead of print in the American Journal of Kidney Diseases. During the harvest, cane cutters and irrigators had the greatest increases in NGAL levels, whereas cane cutters and seeders had the greatest increases in IL-18 levels.
Results also showed that electrolyte solution consumption was associated with lower mean NGAL and NAG levels among cane cutters and lower mean IL-18 and NAG levels among seed cutters. The researchers observed no overall effect of hydration among all workers.
Additionally, on average, workers with the largest increases in NGAL and NAG levels during the harvest had declines in eGFRs of 4.6 and 3.1 mL/min/1.73 m2, respectively.
“Our results are consistent with tubular injury and support the hypothesis that in these workers, repeated subclinical kidney damage may lead to clinically apparent CKD over time,” the authors concluded. “Our findings suggest that for high-risk jobs such as cane cutting, using electrolyte solutions for rehydration during the workday may protect against kidney injury.”
The investigators explained that NGAL is highly upregulated and released into plasma and urine following distal tubule injury. IL-18 is produced by immune and non-immune cells and is excreted in urine following ischemic proximal tubule injury. NAG is shed into urine following proximal tubule injury and indicates structural damage.
Dr. Laws’ team examined workers in 7 job categories: cane cutter, seeder, seed cutter, agrichemical applicator, irrigator, driver, and factory worker. Of these, cane cutters had the greater risk of kidney injury during the harvest, according to the researchers.
“These workers had consistently greater increases in both NGAL and IL-18 levels during the harvest season, suggesting more substantial kidney injury than for workers in other jobs, although irrigators and seeders showed some evidence of injury as well,” Dr. Laws and her colleagues wrote. “Cane cutters have the most physically strenuous sugarcane job; furthermore, they are paid based on their daily work output, a compensation structure that may increase physical strain.”