Extreme weather events, such as hurricanes and other natural disasters, are becoming more and more frequent. These events have also been taking an increasingly grim toll on survivors’ mental and physical health — including the non-humans animals that thrive in disaster-stricken areas.

What’s new — In a new study published in the journal Proceedings of the National Academy of Sciences, researchers analyzed changes to genes involved in the immune system in a group of rhesus macaque monkeys (Macaca mulatta) residing on the Puerto Rican island of Cayo Santiago before and after Hurricane Maria devastated the nation.

“We wanted to study aging after Hurricane Maria to see whether we found support, at the molecular level, for this idea that extreme adversity — particularly from natural disasters — can accelerate parts of the aging process,” Marina Watowich, lead author on the study and a graduate student in the SMack Lab at the University of Washington, tells Inverse.

They found that adult macaques that lived through Hurricane Maria experienced accelerated aging, showing changes in their DNA corresponding with monkeys two years older than them. When scaled to humans’ current average lifespan, that difference in gene expression translates to a whopping seven to eight years of human life.

The changes in DNA correspond with “natural changes in immune gene expression that occur with age,” Noah Snyder-Mackler, a co-author on the study and an assistant professor at the Center for Evolution and Medicine at Arizona State University, tells Inverse.

Why it matters — While the study was done in macaques, the findings could have troubling health implications for humans experiencing increased natural disasters in the coming years.

The scientists also found the hurricane may have disrupted the expression of “molecular chaperone” genes involved in protein folding; irregularities in protein folding have been implicated in age-related diseases like Huntington’s and Alzheimer’s disease. Previous research, the study notes, has found associations between susceptibility to these diseases and extreme adversity.

“There have long been connections made between surviving extreme disasters or traumas and prematurely developing cardiovascular and other diseases,” Watowich says.

“Like human populations faced with natural disaster, the monkeys in this study experienced habitat degradation, changes to their social relationships, and, of course, the stress of living through a terrifying, life-changing event,” Jenny Tung, an associate professor of evolutionary anthropology at Duke University, tells Inverse.

Tung was not a co-author on the paper but contributed data to the study’s analysis and has worked with Snyder-Mackler before.

She also notes many physiological and evolutionary similarities between macaques and humans, so “this type of research can therefore provide a lot of insight into what happens in our own species when confronted with disasters.”

The paper’s conclusions are also relevant for another sobering reason: Climate change-related natural disasters like hurricanes are on the rise, exposing millions more Americans to costly and potentially deadly flood risk by 2050.

Watowich stresses that the study’s findings highlight how we must mitigate “damages from severe weather-related events as much as possible so that when disaster strikes, everyone can recover quickly.”

How they made the discovery — The researchers had a hunch: By inflicting prolonged and severe stress, natural disasters like hurricanes would speed up aging in bodies on a molecular level.

However, because natural disasters are hard to predict, conducting studies on their health effects is also challenging.

But the researchers received a rare opportunity: the ability to study the same group of animals before and after Hurricane Maria. Scientists have studied the 1,800 free-ranging rhesus macaques on Cayo Santiago for years, providing a treasure trove of invaluable data on what they were like before the hurricane struck.

“We wanted to study aging after Hurricane Maria to see whether we found support, at the molecular level, for this idea that extreme adversity — particularly from natural disasters — can accelerate parts of the aging process,” Watowich says.

Immune cell genes change or get “expressed” differently as animals and humans naturally age. So, to test whether macaques experienced accelerated aging after Hurricane Maria, the researchers analyzed how the natural disaster may have similarly affected immune cell expression in specific genes.

The researchers compared samples taken one to four years before the hurricane to samples taken one year afterward. The scientists then tested for hurricane-associated differences or genetic signatures in immune cells using RNA sequencing — a method that helps analyze gene expression.

Finally, the researchers used human genetic age predictors to estimate the amount of accelerated aging that occurred in the primates. The results were alarming.

What it means — According to the study, the findings “support the idea that the peripheral immune system is altered following an extreme adverse event,” thereby helping to explain how natural disasters exacerbate health issues and increase mortality.

But there’s still a lot researchers don’t understand. For one, they aren’t totally sure why these biological, age-associated changes are occurring in primates after Hurricane Maria.

They suspect the hurricane itself did not damage the body’s immune cells. Instead, “the lasting damage to the environment” on the island of Cayo Santiago led to chronic stress and accelerated aging in the macaques.

“This chronic activation of the stress response can wear down the body and lead to long-term immune changes similar to those that happen during aging,” Snyder-Mackler says.

What’s next — If there’s a “silver lining” to the grim findings, Snyder says it lies in the difference in aging between primates on the island. While many macaques experienced faster aging, others did not.

“What makes some monkeys more resilient to the negative effects of the hurricane?” he asks. Future research will tackle this question “to inform how to help humans recover and protect their health after experiencing a natural disaster.”