Background Performing strenuous physical activity in a heat environment with high air pollution has been associated to kidney injury in healthy individuals. The aim of this study was to evaluate the acute effects on the kidney of manual harvesting of sugarcane and supervised streets running exercise.

Methods We evaluated 49 male sugarcane workers, three months after harvesting beginning, before and after a daily work shift, and 39 male Brazilian army recruits, six months after performing street running five days a week, before and after a 7.5km (45 min) street running. Urine and blood samples were assessed for inflammatory markers, kidney biomarkers and renal function. Glomerular filtration rate (GFR) was estimated by CKD-EPI equation. Particulate matter (PM_2.5) and environmental temperature at sugarcane field during working days, and at street circuits during races, were monitored. Continuous variables are described by mean±SD or median(IQR).The differences between post and pre values are presented with their 95% confidence interval. Analyses were performed with SPSS (v21) software.

Results PM_2.5 concentration and temperature were higher in sugarcane field: 101.0 μg/m³ (IQR: 31.0–139.5) and 29.7°C (24.1–34.0) compared to urban environment: 62.0 μg/m³ (37.5–103.0) and 22.2°C (20.9–23.5). Sugarcane cutters were older (41.3±10.6×19.1±1.0 years). There was significant and similar reduction of GFR in harvesters and recruits:-15.0 [95%CI:-18.3;-11.7]mL/min/1.73m² after shift work, and -14.1 [-18.1;-10.1] post-run, respectively; similar increase in serum creatinine (0.17[0.13;0.21] and 0.13[0.10;0.16]mg/dL) and in urinary KIM-1 (119.6[-1.5;240.6] and 427.1[168.7;685.5]pg/mL). There was increase in serum NGAL (8.9[2.5;15.2]ng/mL after shift work and 2.7[-18.5;23.9] post-run) and in blood monocytes (42.4[2.0;82.7]/mm³ after shift work and -52.6[-120.7;15.4] post-run) observed only in sugarcane cutters, and blood neutrophils increase in both groups, which was higher in cutters: 1846[1349;2343] vs 400[150;649]/mm³ in recruits.

Conclusion Burned sugarcane harvesting and street running were associated with acute decline in kidney function, increase in biomarkers of renal injury and systemic inflammation, with more marked changes in sugarcane workers. These alterations are likely associated with the extraneous physical work, heat stress, air pollution and dehydration. The two groups evaluated showed differences that make it difficult to compare them. However, we were able to show the impact that physical activity in adverse conditions had on the studied outcomes. The effects of a daily repetitive kidney stress and inflammation are unknown, but may evolve to chronic disease in vulnerable individuals. Measures should be taken to improve the working conditions of sugarcane cutters, including cessation of burning of sugarcane, establishment of breaks and better hydration at work.