A new population-based study published in The Lancet has found that Tamil Nadu’s agricultural workers face a growing risk of kidney disease linked to heat exposure, dehydration and long outdoor work hours.
Conducted between August and December 2023, the Chronic Kidney Disease of unknown etiology (or uncertain cause) CKDu – AGRI study surveyed agricultural workers across all five agro-climatic zones of the State — the North-East, North-West, Western, Cauvery Delta, and Southern regions. Using a stratified multi-stage cluster sampling method, researchers studied 3,350 farm workers from 125 villages, collecting data on occupation, health and environmental exposures.
Heat and kidney injury
The researchers observed a striking seasonal variation in kidney function. During August — one of Tamil Nadu’s hottest months — 17.4% of participants had an estimated glomerular filtration rate (eGFR) below 60 mL/min/1.73 m². When tested again in December, kidney function had returned to normal in most.
“These were asymptomatic, sub-clinical episodes of acute kidney injury,” says R. Sakthirajan,co-author of the study, senior assistant professor, Institute of Nephrology, Madras Medical College. “Because all assays were done in a single reference laboratory, the variation almost certainly reflects physiological stress rather than measurement error.”
The team point out that these transient injuries are linked to repetitive heat and dehydration stress during fieldwork — a pattern also documented in Central America and Sri Lanka. “We plan to follow participants across different seasons to track kidney markers, hydration, and individual heat exposure,” adds Sudharshini Subramaniam, co-author of the study, associate professor, Institute of Community Medicine. “This will help confirm whether repeated seasonal stress leads to chronic kidney disease over time.”
Risk factors
The study found an overall CKD prevalence of 5.31%, with nearly half of these cases classified as Chronic Kidney Disease of Unknown aetiology (CKDu) — that is, not linked to diabetes, hypertension or heart disease. The burden was significantly higher in the North-East (7.68%) and Southern (6.4%) zones compared to the North-West (2.16%).
The Universal Thermal Climate Index (UTCI) used to model heat exposure showed levels above 38°C for more than four hours per day – an indicator of “very strong heat stress” across the North-East and South in August. Workers with CKD spent an average of 36.18 hours a week outdoors, compared to 33.42 hours among those with normal kidney function. For those with CKDu, the average was even higher, at 38.07 hours.
Risk factors included older age (above 53.5 years), male sex, hypertension, anaemia, history of renal stones, smokeless tobacco use, and long hours of outdoor work. Interestingly, factors such as potable water source, snake bite, COVID infection and alcohol intake showed no association with CKD prevalence. The prevalence was 7.9% among those without formal education, compared to 2.5% among graduates.
The prevalence of diabetes (13.4%) and hypertension (30.6%) was similar to national averages, yet two-thirds of people living with hypertension and 40% of people living with diabetes were newly diagnosed during the study, underscoring low awareness.
The researchers note that the Tamil Nadu findings mirror global CKDu “hotspots” — first reported among sugarcane and corn workers in El Salvador and later in Nicaragua, Mexico and Panama where heat and dehydration are suspected to play a key role.
Preventive measures
“Simple preventive measures can help,” says Gopalakrishnan Natarajan, co-author of the study, member secretary of TRANSTAN and former Director, Institute of Nephrology. “Following the Water–Rest–Shade protocol around 750 mL of cool water every hour and 10–15 minutes of rest each hour can protect workers from heat strain.”
The researchers also recommend flexible work hours to avoid peak heat, and the inclusion of renal function monitoring in routine occupational health checks. At a policy level, they point to the absence of heat-specific labour standards in India. “There is an urgent need to integrate heat-stress thresholds and kidney health monitoring into workplace safety frameworks,” the team notes.
Need of early detection
Only 1.6% of participants reported symptoms such as swelling, and nocturia — waking at night to urinate was the only common complaint, seen in 12.9%. “The silent profile of CKD means symptom-based diagnosis misses most cases,” says Dr. Subramaniam.
The authors recommend annual serum creatinine and urine albumin–creatinine testing for agricultural workers through existing primary health programmes. Village health nurses and multipurpose health workers could be trained to identify high-risk groups — men above 50, those with anaemia, tobacco users and those exposed to prolonged heat.
Expanding access to education and implementing tobacco-cessation measures, they suggest, may also help reduce risk. As Tamil Nadu faces hotter summers, the study urge that kidney health must become part of India’s climate and labour policy.
Published – October 30, 2025 07:57 pm IST
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