A non-optimal temperature is any outdoor or ambient temperature that falls above or below the ideal range where human health, body function, and survival risk are best maintained.
Non-optimal temperature — as used in the Global Burden of Disease (GBD) refers to both acute cold and acute heat exposures that deviate from a theoretical minimum risk exposure level, and it is now recognized as one of the top five attributable risk factors for CKD-related disability-adjusted life years (DALYs), accounting for approximately 4.4% of the global CKD burden.
It includes both extreme cold and extreme heat.
A departure from a local “minimum mortality temperature,” which is the specific baseline range where health risks are lowest.
Increases risks for heart attacks, strokes, breathing trouble, and overall illness.
Global Impact: Accounts for a large share of worldwide weather-related deaths, with a high portion linked to cold snaps.
Vulnerability: Affects older adults, outdoor workers, and people with chronic health conditions the most.
Historically, cold has contributed a greater share of the CKD mortality burden than heat — in 2019, the age-standardized mortality rate attributable to low temperature was approximately 1.05 per 100,000 versus 0.10 per 100,000 for high temperature.
However, the burden attributable to high temperature has been rising rapidly, particularly in tropical and low socio-demographic index (SDI) regions, and is projected to accelerate with climate change.
Epidemiologic Evidence
For each 1°C increase in annual average temperature there is an associated with a 0.23 percentage-point increase in diagnosed CKD prevalence and an additional 1.37 ESKD cases per 100,000 population.
Heat wave days were positively associated with both outcomes, with stronger associations at higher temperature thresholds and longer durations, and in high-poverty and nonmetropolitan counties.
For every 1°C increase in temperature, kidney-related morbidity increased by 1% and kidney-related mortality increased by 3%, with the greatest morbidity risk for urolithiasis.
Heatwaves amplified these effects, with low-intensity heatwaves increasing kidney morbidity by 5.9% and high-intensity heatwaves by 7.7%.
A Taiwanese cohort study found that patients with heat injury had a dramatically increased risk of CKD and ESRD compared to controls.[5]
Pathophysiological Mechanisms
Dehydration and hyperosmolarity: Volume contraction activates vasopressin and the aldose reductase/polyol pathway, generating oxidative stress in renal tubular cells
Subclinical rhabdomyolysis: Physical exertion in heat causes myoglobin release, leading to tubular injury
Urate crystalluria: Heat stress and dehydration elevate serum urate, promoting crystal deposition in renal tubules
Direct thermal injury: Elevated core temperature causes renal ischemia, oxidative stress, and inflammatory cascades with proximal tubular cells being particularly vulnerable
Potentiation of toxin-mediated injury: Volume contraction enhances reabsorption of nephrotoxins in the proximal tubule.
Non-optimal temperature is a central hypothesis in the epidemic of CKDu (CKD of non-traditional causes), which disproportionately affects young male agricultural workers in tropical regions of Central America, Sri Lanka, and India.
These patients characteristically lack diabetes, hypertension, or glomerulonephritis, and kidney biopsies show chronic tubulointerstitial nephritis. A meta-regression found that each 1°C increase in temperature in CKDu-endemic regions was associated with an 8% increase in CKD risk.
Other non-traditional risk factors include drinking well water, malaria, low water intake, and agrochemical exposure.
The GBD 2023 analysis noted that the more rapidly progressive and deadly course of CKDu may account for increasing age-standardized CKD deaths and DALYs in tropical and subtropical regions, and that climate change — through rising average temperatures and more frequent extreme weather events — is likely to cause a further rise in CKD attributed to non-optimal temperature.
Groups at highest risk from temperature-related kidney disease include males, agricultural workers under 50, adults ≥65 years, individuals of low socioeconomic status, residents of rural/tropical/subtropical regions, and patients already on hemodialysis (who have impaired thermoregulation).
Among hemodialysis patients, each 1°C increase in daily maximum temperature was associated with a 7.5% increase in all-cause mortality.
Under high-emission climate scenarios, the global age-standardized incidence rate of CKD could increase by nearly 148.5% by 2100, driven in part by maximum temperature variability.
There is a need for heatwave early warning systems, improved hydration strategies for outdoor workers, and early CKD screening in vulnerable populations.