December 9, 2021 // Editor's note: This story has been updated to clarify that this study shows an association between climate change and kidney disease, but not that climate change causes such disease.
A number of cities in Brazil can already see and measure the potential effects of climate change on human health, reports a study recently published in The Lancet Regional Health – Americas.
Scientists studied 2,726,886 hospitalizations for kidney disease in Brazil between 2000 and 2015 and found that 7.4% of total hospitalizations could be directly attributed to the increase in ambient temperature.
Conducted by Bo Wen, a PhD candidate, and other researchers from Monash University in Melbourne, Australia, as well as scientists from the University of São Paulo, the study is the first to assess the relative risk and rate of hospitalizations due to temperature-related renal diseases in almost 80% of the country's population using a dataset from the Brazilian Unified Health System (Sistema Único de Saúde, SUS).
The authors found that for every 1°C increase in daily mean temperature the relative risk of renal disease increased by 0.9%, after adjustment for several variables and comparison with the historical data series.
"Follow‑ups have shown that when Brazilian cities go out of their respective thermal comfort ranges, the most vulnerable segments of the population — children and the elderly — are at greater risk of having to go to the hospital to treat a renal disease," said one of the authors, Paulo Saldiva, MD, PhD, a researcher at the Institute of Advanced Studies and professor of pathology at the University of São Paulo in Brazil.
Specifically, children aged 0-4 years comprise the most affected group, with a 3.5% increase in relative risk for each 1°C increase in temperature. Females were the next most affected group (1.1%), followed by individuals over 80 years of age (1.0%). Cases were classified into three categories: glomerular diseases, renal tubulo-interstitial diseases, and kidney failure.
Researchers found differences were also dependent on patient location: the risk of hospitalization for renal disease was higher in the north (2.2%), which tends to be hotter and more humid, than the southeast (0.7%).
"This nationwide study provides robust evidence that more policies should be developed to prevent heat-related hospitalizations and mitigate climate change," they conclude.
Effects of Heat on Vulnerable Populations
The researchers note in their article that previous studies have been conducted in developed countries and were relatively small, preventing them from evaluating whether associations with ill health varied by sex, age, and region.
Large temperature variations, such as those experienced when going from the hot sun during the day to shivering cold at night, have an impact on the body, and on the kidneys in particular, that can persist for 2 days, they explain.
Children are particularly vulnerable because the body's ability to regulate temperature isn't fully developed at a young age.
"Preterm babies need to be put in an incubator because their thermoregulation mechanisms are developing. It is the same as when a young child with an ear infection or tonsillitis has a fever. They aren't capable of fine-tuning it, something that they will be capable of doing in time," noted Saldiva. Children also have a higher body-surface-area-to-mass ratio than adults, leaving them more exposed.
Females are also more vulnerable to heat because, proportionally, they have more body fat due to evolutionary factors, Saldiva explained. Variations in estrogen also interfere with the flexibility of blood vessels and with the thermoregulatory center.
And in the elderly, the "biological thermostat" that controls body temperature is affected by factors such as subcutaneous fat atrophy, which leads to loss of protection against temperature changes. Changes in the brain can also cause autonomic responses to become slower. For example, it is common for the elderly to lose their subjective sensation of thirst during a heatwave as they have an impaired ability to detect osmotic concentration.
All these situations force the kidneys to work harder.
"The kidneys absorb a large amount of fluid throughout the day, especially during periods of dehydration. If you measure the partial pressure of oxygen in kidney tissue, you will find that it is one of the lowest in the body. That is because this organ uses a lot of energy, a lot of oxygen," Saldiva explained.
"And the more the organ works, the more energy it consumes. Indeed, observations made on workers in the Antilles, southeast Asia, and even in some cases in northeast Brazil, have indicated that the type of exhausting work done in intense heat and causes excessive sweating can cause kidney failure in young people," he noted.
One such report, which estimated there has been a surge of kidney failure deaths blamed on heat exposure in around 50,000 younger people, was discussed at a kidney disease meeting in 2017, as reported by Medscape Medical News.
Brazil: A Natural Laboratory
The researchers chose to study Brazil because, thanks to SUS records, it has good health-related data as well as diverse regional climates, which range from tropical to cool temperate.
They characterized the relationship between ambient temperature, renal disease, and increase in corresponding hospitalizations and emergency room visits, and adjusted for variables including age, sex, and region.
A significant number of Brazilians suffer from arterial hypertension and diabetes that is not properly managed, all of which add to the burden of comorbidities in the population and to social disparities.
"Brazil presents us with a natural laboratory in terms of the relationship between the environment and social inequality," Saldiva summarized.
The study was the work of many individuals, he stressed, including authors from China as well as an expert in biometeorology, Micheline Coêlho, PhD, who is a researcher at the University of São Paulo and is studying medicine at Monash University, a leading center in the field of environmental epidemiology focusing on climate.
Like Saldiva and the other authors, Coêlho is part of the international Multi-Country Multi‑City (MCC) Collaborative Research Network.
The MCC studies 470 cities worldwide to see whether consistent changes in climate vary according to latitude and examine whether changes in climate affect rates of illness and death.
"The MCC has already published many articles in prestigious journals, but Latin America almost never appears. We decided to set up work in parallel, also taking advantage of the data and conditions that we have in Brazil...to increase this representation," said Saldiva.
This story originally appeared on the Portuguese edition of Medscape.
Lead Image: Dreamstime
Medscape Medical News © 2021 WebMD, LLC
Send comments and news tips to email@example.com.
Cite this: Climate Change Associated With Kidney Disease - Medscape - Dec 08, 2021.