Stopping Amazon deforestation leads to lower hospital cases

Trees and forests are often described as lungs of the earth due to their important role removing pollutants like carbon dioxide from the environment. It's becoming clearer that forests help to make us healthier too.

New research from the University of Bonn in Germany and Universidade Federal de Minas Gerais in Brazil has analyzed local health outcomes after conservation measures in the Amazon.

It found that these measures led to a reduction in the hospitalization and death rate due to respiratory health problems in the local population.

The positive impact on people's health was due to a reduction in forest fires. The conservation measures reduced fine particulate concentrations in the air—a main vector for adverse health effects of fire smoke.

"The relationship between the fire outbreak and the smoke travelling somewhere and people inhaling it and then getting health problems is pretty straightforward," said the study's lead author Yannic Damm, University of Bonn, Germany.

Fewer forest fires saw fewer deaths, hospitalizations

Amazonian wildfires are a persistent topic on South America's environmental agenda. 2024 saw Brazil's worst wildfires in 14 years.

Across the border in Bolivia, land clearing was blamed in part for fires that burned through a record 10 million hectares. 

The researchers wanted to understand what impact deforestation policy changes might have on health outcomes in the Amazon.

They first calculated whether fires and air pollution decreased after policies introduced in 2007 and 2009 to stop traders purchasing soy and cattle products grown on deforested land.

The study investigated a 100km zone surrounding the border of the Amazon biome across the states of Maranhão, Tocantins, Pará, Mato Grosso and Rondônia. 

A reduction in forest fires was observed in the years after the introduction of these policies. It resulted in sizeable drops in concentrations of pollutant gases like carbon monoxide, nitrogen and sulfur dioxides.

They then compared hospitalizations for a range of diseases associated with air pollution to the reduction in fires and particulate readings.

Within the Amazon region, they estimated improved conservation outcomes led to a decrease in around 18,000 hospitalizations and avoided around 680 deaths per year due to smoke and fire-related health problems.

To verify their estimations, they benchmarked these intakes against those for sexually transmitted infections (which shouldn't be influenced by fire rates) and found these remained stable within the same time period.

How do forest fires damage health outcomes?

Cleared tropical forests can result in hotter and drier conditions that leave regions more prone to hotter and more intense wildfires — either from natural or human causes.

Wildfire smoke — and air pollution generally — contains fine particulate matter, sometimes called PM2.5, intermixed with a cocktail of toxic gases.

PM2.5 are particulates smaller than 2.5 micrometers, that's smaller that a tiny bacterial cell. Larger PM10 are 10 — slightly bigger than a red blood cell.

Such is their size that they are easily absorbed into the bloodstream through the lungs, leading to potential health problems in the short and long term.

Smoke exposure can aggravate conditions like asthma and reduce lung function. Chronic problems emerging from prolonged exposure can include an increase in the rate of heart and respiratory diseases.

Smoke isn't the only health risk caused by deforestation

While forest fires and respiratory health outcomes are more likely in areas impacted by deforestation, the practice of tree felling can also increase the likelihood of transmissible disease.

That's because forest clearance reduces habitat for other plants and animals, which may bring them into closer contact with humans.

This becomes problematic when animals become reservoirs for diseases caused by viruses, bacteria, or parasites.

"When you deforest an area, it's not always associated with an increase in infectious disease, but in many cases it can lead to spillover of pathogens from wildlife to people and their domestic animals," says Nicole Lynn Gottdenker, a disease ecologist at the University of Georgia, US.

When habitat removal translates to changes in ecological communities, it might be easier for "reservoir" animals to make contact with humans.

Multiple studies have shown malaria transmission in the Amazon is linked to deforestation. One study found a 1% increase in monthly Amazon tree felling was associated with a 6.3% increase in malaria cases.

Forest loss can also directly impact humans and make them more vulnerable to pathogens.

"Often, people become displaced and marginalized and are often the most hit by these pathogens and these transmission in infectious diseases" said Gottdenker.

Studies are showing that policies aimed at reducing deforestation and habitat loss can  lower the chances of so-called zoonotic spillover events, which include recent examples of the SARS-CoV-2 virus (the cause of COVID-19) and Mpox.

Edited by: Fred Schwaller

Sources:

Damm, et al., Health benefits of reduced deforestation in the Brazilian Amazon. Commun Earth Environ 5, 693 (2024).https://doi.org/10.1038/s43247-024-01840-7

Arisco et al.,  Ecological change increases malaria risk in the Brazilian Amazon, Proc. Natl. Acad. Sci. U.S.A. 121 (44) e2409583121, (2024).https://doi.org/10.1073/pnas.2409583121 (2024)