PURPOSE: The extent to which groundskeepers experience heat strain, dehydration, and accompanying declines in kidney function during work in hot-humid conditions is unknown.
METHODS: Hydration, cardiovascular, and internal body temperature measures were assessed in 20 groundskeepers (18 men; mean±SD age=38±8 y, body mass index=32±8 kg/m2) during work on 2 summer days. Before (PRE) and after (POST) the work shift, resting blood pressure (BP) and heart rate (HR) were measured and urine and blood samples were collected. At POST, fluid intake was recalled for the previous 24 h. Gastrointestinal temperature (TGI) was recorded every 5 min via ingestible telemetric sensor.
RESULTS: Average highest daily wet bulb globe temperature=39.1±3.5 °C. In 45% of subjects, PRE BP>130/80 mm Hg on Day 1 (D1) and Day 2 (D2). Highest HR and TGI achieved across both days were 143±15 bpm and 37.7±0.3 °C, respectively. On D1 and D2, urine specific gravity (USG; 1.021±01) and urine color (UCOL; 6±1) did not change PRE to POST (all P>0.28), but subjects began the workday “underhydrated” (concentrated urine but normal serum osmolality (Sosm)]—62% had USG≥1.020 and 95% had UCOL≥4 despite Sosm=292±5. Fluid intake=2.3±1.6 L during work and consisted of 70% water and 25% sugar sweetened beverages. No subject lost ≥2% of body mass on D1 or D2. For 6 subjects, estimated glomerular filtration rate at PRE was ≤60 mL/min/1.73m2 averaged across D1 and D2. Although serum creatinine did not change statistically from PRE to POST across days (all P>0.18), 5 subjects had increases ≥0.3 mg/dL, signifying an acute kidney injury (AKI).
CONCLUSIONS: While hyperthermia was not prevalent, subjects began and ended the workday underhydrated. Hypertension, obesity, and low water intake may have contributed to the overall low kidney function and AKIs observed. Using urine color as a self-assessment tool could be a beneficial intervention improve hydration status and kidney function.Funded by NIOSH
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