Agricultural workers who experience high levels of heat exposure and volume depletion over the course of a work shift – a change in body mass due to inadequate hydration and strenuous labor – are at danger of acute kidney injury (AKI), and workers paid by the piece face a higher risk, concludes new research from UC Davis.

The study is the first in the United States to examine the association of occupational heat exposure and volume depletion on kidney function to the knowledge of UC Davis COEH Director and Principal Investigator Marc Schenker, distinguished professor of Public Health Sciences and Medicine.

According to the paper published in the January 2017 issue of the journal, Occupational and Environmental Medicine, the development of AKI may lead to further kidney damage, including chronic kidney disease, as it is unlikely that workers know they are damaging their kidneys while working in the fields.

In a study of 283 agricultural workers at 15 locations in the Central Valley of California, researchers measured levels of serum creatinine in blood samples taken pre-and post-shift. Heat exposure measurements were estimated by changes in core body temperature. They estimated volume depletion in workers by measuring changes in body mass over the work shift.

Their analysis took into account traditional risk factors such as age, diabetes, hypertension, and a history of kidney disease and occupational risk factors including years employed as a farmworker, method of pay, and farm task.

Researchers identified 35 participants with incident AKI over the course of a work-shift, or more than 12 percent of the study sample. They found workers who experienced high levels of heat exposure and those paid by the piece instead of hourly were most vulnerable.

“Surprisingly, we found a dose-response inverse relationship of weight classification and AKI, wherein those classified as obese had lower odds of developing AKI than those classified as normal weight,” report the authors, who suggest these participants may have modified or reduced their work load. Of note, obese workers had lower rates of being paid by the piece – a practice that motivates workers to boost their earnings by skipping rest and hydration breaks – behaviors that are protective of heat exposure and AKI.

Lead author Sally Moyce concludes that although occupational regulations are in place to protect employees from heat-related illness, farmworkers who experience high levels of heat exposure and who are paid by the piece are at increased risk of AKI. She points out, by addressing these risk factors, incident AKI associated with heat exposure and piece-rate work may be prevented. Schenker notes that the long term consequences of AKI in these workers are unknown as this was only a short term study.

In addition to Schenker and Moyce, a graduate student in the Betty Irene Moor School of Nursing, co-authors include COEH Research Associate Diane Mitchell; Tracey Armitage, statistician, UC Davis; Daniel Tancredi, director of the Statistics and Data Management Core of the UC Davis CounterACT Center of Excellence; and Jill G. Joseph, professor, Betty Irene Moore School of Nursing.

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