As temperatures rise, so does risk of kidney disease, study finds

The impacts of burning fossil fuels are not only being felt in the environment, but are also affecting human health. The most known and studied trends to date have been on the direct links between fossil fuel combustion and respiratory illnesses, especially in urban areas. But a new study points to a broader-range and longer-term impact that’s no less severe: the correlation between higher temperatures, caused by carbon emissions, and the incidence of kidney disease.

A group of international scientists including researchers from the University of São Paulo (USP), carried out an unprecedented study that crossed data on high temperatures and the rise in cases of patients with kidney problems. The researchers found that the perspiration caused by high temperatures and the consequential dehydration play a vital role in the development of kidney disease.

The study, by scientists in Brazil and Australia, focused on records from Brazil’s national public health system, or SUS, in 1,816 Brazilian cities. It showed that from 2000-2015, more than 200,000 cases of kidney disease were directly related to changes in the climate. Effectively, for every 1° Celsius (1.8° Fahrenheit) rise in temperature, the estimated risk of hospitalization for kidney problems lasting up to seven days rose by 0.9%.

“We already knew that temperature had an effect on kidneys because doctors have always known this. However, there had never been a study this size done on the topic,” said study co-author Micheline de Sousa Zanotti Stagliorio Coêlho, a mathematician and meteorologist at the University of São Paulo (USP).

Fellow author Paulo Hilario Nascimento Saldiva, a professor at USP’s medical school, said previous studies already show increased frequency of kidney disease among, for example, farm workers like sugarcane harvesters in Central American countries. “We already knew that it wasn’t just the heart and lungs that are affected by the heat,” he said.

Now, this study confirms these findings. “Crossing data clearly shows the negative impact of high temperatures on the renal system as well,” Coêlho said.

Children, women and the elderly at highest risk

The researchers found increased perspiration caused by high temperatures and the resulting dehydration play a vital role in the development of kidney disease. The kidneys’ main functions include removing impurities and toxins from the body, regulating water and maintaining the balance of minerals like sodium, potassium and phosphorus, and releasing hormones that maintain blood pressure and regulate the production of red blood cells.

The authors of the study, published in leading medical journal The Lancet, note that kidney disease is already considered a global public health concern. It was responsible for 2.59 million deaths in 2017, up 26.6% from 2007.

In Brazil, data from the Brazilian Nephrology Society show that more than 10 million people suffer from some type of kidney disease. In chronic cases, it’s associated with two other conditions that are common in the Brazilian population: high blood pressure and diabetes.

The study analyzed data from 2.7 million cases of kidney disease at public hospitals in Brazil (within the public SUS system) over the past 16 years. It found that the risk of hospitalization as a result of warmer temperatures was higher in women, children under the age of 4, and people over 80.

Saldiva said the risk to very young children could be explained by the fact that, in general, their natural “thermostats,” or ability to regulate body temperature, are not fully developed; in the case of older people, this same ability is beginning to show signs of wear and tear. Older people become dehydrated more easily because they don’t feel the sense of thirst as strongly. In women, meanwhile, the thermoregulation system is different than that in men, due to their naturally higher percentage of body fat for pregnancy and breastfeeding, which makes them more vulnerable to heat.

“They also have a greater propensity to develop other autoimmune diseases like lupus, which is likely to damage the kidneys,” Saldiva said.

Overloading the public health system

While a 0.9% increase in hospitalization of patients for kidney problems due to rising temperatures may seem low number, when extrapolated across a large population, like in Brazil, the attributable risk becomes high, the study authors say.

This then has a direct impact on the public health system, Saldiva said. The International Society of Nephrology reports that 90,000 Brazilians are on dialysis today, double the number from 10 years ago. And the cost of the procedure has more than doubled, from $340 million in 2000 to $713 million in 2009.

“Dialysis is expensive, the medications are expensive. Both for the health system and for families,” Saldiva said. “People suffering from kidney disease have greater chances of dying young or retiring early because of disability, which puts even more pressure on the social security system in Brazil.”

The study identifies Brazil’s north and northeast regions as the areas most affected by this jump in hospital admissions associated with global warming. In the southeast, while temperature peaks are more frequent, there’s greater variation in temperature throughout the day, whereas in the northern regions the heat is constant and prolonged, which affects kidney function over the long term.

“And once again, we see that the poorer population in the north and northeast will suffer more. The humbler and more vulnerable are the ones that will pay the higher price,” Coêlho said.

Global warming and human health

Saldiva said the study’s findings underscore the urgency of dealing with climate change impacts immediately, instead of seeing it as a problem that can still be staved off.

“Global warming is now. Our bodies are already responding to it with illnesses. The impacts of the climate crisis stretch beyond flooding, landslides and epic droughts. Climate change is costing us now!” Saldiva said. “People’s health depends on our not destroying the environment. Human health is a part of the ecosystem.”

The World Health Organization (WHO) estimates that between 2030 and 2050, the climate crisis will be responsible for 250,000 deaths each year due to malnutrition, malaria, diarrhea and heat stress. In what it already calls “the greatest health threat that humanity has ever faced,” the WHO says developing countries like Brazil will be less prepared to deal with the problem.

 
Citation:

Wen, B., Xu, R., Wu, Y., Coêlho, M. D., Saldiva, P. H., Guo, Y., & Li, S. (2022). Association between ambient temperature and hospitalization for renal diseases in Brazil during 2000-2015: A nationwide case-crossover study. The Lancet Regional Health — Americas, 6, 100101. doi:10.1016/j.lana.2021.100101

Banner image by Fernando Frazão/Agência Brasil.

This story was reported by Mongabay’s Brazil team and first published here on our Brazil site on Nov. 23, 2021.