Researchers at the University of Oregon have been monitoring epidemics of chronic kidney disease of non-traditional origin (CKDnto) in Central America (particularly among manual labourers), Sri Lanka and India that are potentially associated with physically demanding work in a high temperature environment.[i]
Despite ‘growing concern’ that workers in the US are suffering with CKDnto, there are limited reports of cases ‘related to’ occupational heat exposure. It is unclear if this is due to a lack of appropriate study on CKDnto, or whether the wide-ranging climate, accessibility to healthcare and protective working conditions (e.g. air conditioning) have obscured a relationship. Alternatively, it could be an issue of underreporting.
There appears to be a ‘significant gap’ in the literature, with no study to-date having investigated whether ‘in situ occupational heat exposure increases markers of kidney injury among US workers’. However, the Occupational Safety and Health Administration (OSHA) recognises that millions of workers (outdoor and indoor) are exposed to heat stress, so a link with CKDnto is theoretically ‘plausible’. What is more, Flouris et al (2018) recently reported that 15% of individuals who frequently work in hot environments worldwide present with chronic or acute kidney disorders.[ii]
There is no scientific consensus on whether heat stress is the primary causal agent of injury, accelerates the existing underlying pathology (e.g. traditional risk factors of kidney disease), or increases susceptibility to other injurious exposures (e.g. environmental/chemical nephrotoxins), but it is possible that heat stress acts as a catalyst, in the context of physically demanding work, by increasing core temperature. Regardless of the exact biological mechanism, current evidence supports the hypothesis that heat stress can induce low-grade kidney injury, or overt acute kidney injury (AKI) [or acute tubular necrosis (ATN)] and that repeated injuries may progress to the eventual development of CKDnto.
Going along with this hypothesis, the University of Oregon team conducted a narrative mini review to preliminarily identify populations of workers at greater risk of ill health. Inspecting the available literature, they characterised the demographics, environmental conditions, physiological strain (increased core body temperature, heart rate and dehydration) and work durations in US industries typically affected by occupational heat exposure, such as farming, wildland firefighting, landscaping, and utilities.
In the Regulatory, Integrative and Comparative Physiology journal (part of the American Journal of Physiology),[iii] they admitted to finding ‘surprisingly limited’ evidence characterising work in hot conditions, supporting the need for further investigation.
That being said, there were signs that ‘some workers in the US may experience conditions that are similar to those in countries with workers that have high rates of CKDnto’.
If work in heat is not causing adverse health conditions in the US at present, the study authors expect that it will do in the near future.
Indeed, the National Academies of Sciences, Engineering and Medicine submits that heat waves are getting ‘longer, more extreme and more frequent’, thanks to climate change – or more specifically – global warming.[iv]
Lead Author, Chris Chapman, also warns that the US should be ‘paying attention’ to CKDnto incidence because a large percentage of the population exhibit lifestyle-based risk factors prone to trigger kidney disease, including obesity, high blood pressure and diabetes. The nation could foreseeably be disproportionately impacted.
With global temperatures forecast to rise in time, the UK may likewise have to contend with escalating cases injury affiliated with acute exposure to extreme heat. This was a topic we explored in edition 189 of BC Disease News (here) and CKD was discussed.
The Health and Safety Executive lists UK workers in glass and rubber manufacturing plants; mines; compressed air tunnels; conventional and nuclear power plants; foundries and smelting operations; brick-firing and ceramics plants; boiler rooms; bakeries and catering kitchens; and laundries as being vulnerable to ‘heat stress’.[v]
[i] University of Oregon, ‘WORKING IN INTENSE HEAT MAY RAISE RISK OF KIDNEY DISEASE’ (20 July 2021 Futurity) https://www.futurity.org/kidney-disease-heat-temperature-2598842/> accessed 22 October 2021.
[ii] Flouris AD et al., Workers' health and productivity under occupational heat strain: a systematic review and meta-analysis. Lancet Planet Health. 2018 Dec;2(12):e521-e531. <https://www.thelancet.com/action/showPdf?pii=S2542-5196%2818%2930237-7> accessed 22 October 2021.
[iii] Chapman CL et al., Occupational heat exposure and the risk of chronic kidney disease of nontraditional origin in the United States. Am J Physiol Regul Integr Comp Physiol. 2021 Aug 1;321(2):R141-R151. <https://www.researchgate.net/profile/Jason-Glaser/publication/352704764_Occupational_heat_exposure_and_the_risk_of_chronic_kidney_disease_of_non-traditional_origin_in_the_United_States/links/615c6661c04f5909fd807ac4/Occupational-heat-exposure-and-the-risk-of-chronic-kidney-disease-of-non-traditional-origin-in-the-United-States.pdf> accessed 22 October 2021.
[iv] ‘Global warming makes heat waves hotter, longer, and more common’ (23 August 2021 National Academies) <https://www.nationalacademies.org/based-on-science/global-warming-makes-heat-waves-hotter-longer-and-more-common> accessed 22 October 2021.
[v] 'Heat Stress' (HSE) <https://www.hse.gov.uk/temperature/heatstress/index.htm> accessed 22 October 2021.