Does air pollution raise the risk of brain bleeds over time? University of Utah study

Yahoo

12-07-2025

The type of air pollution common in wildfires and smoggy inversions — PM2.5 — may be linked to rare but serious and sometimes deadly brain bleeds.
New research from University of Utah Health has for the first time linked the small particulate matter pollution to ruptured brain aneurysm, which is more formally called aneurysmal subarachnoid hemorrhage. The resulting brain tissue damage can be severe enough to leave patients paralyzed or in a coma, if they survive it.
The study is published in the journal npj Clean Air. The 'npj' indicates it's part of the Nature Partners Journal portfolio.
The findings are preliminary, said lead researcher Dr. Robert Rennert, a neurosurgeon and assistant professor of neurosurgery at the University of Utah. But it's compelling and shows that pollution from a wildfire or smog can have an impact even several months later.
PM2.5 pollution is made up of tiny particles or droplets that are easy to breathe in and can damage lungs and contribute to risk of ischemic strokes. A university news release says PM2.5 pollution particles are 30 times finer than human hair.
Rennert said earlier research has shown negative health effects from the pollution, including increased risk of ischemic and hemorrhagic stroke, as well as neurological, cardiovascular and pulmonary diseases.
'People in the past have naturally thought that there may be a link between air pollution exposure and risk of bleeding from an intracranial aneurysm. These aneurysms occur in 3%-6% of the adult population,' he said.
That type of brain bleed kills about a third of the time, while a like share suffer very severe neurologic injuries," per Rennert.
The study involved a retrospective look at 70 adult patients University of Utah Hospital treated over the course of five years for that type of brain aneurysm. The researchers went backwards from the medical event, looking at close to 13,000 data points to see what the PM2.5 levels were in the days, weeks and months before a brain bleed occurred. Rennert said they wanted to see whether the pollution itself changed each patient's risk of having the hemorrhage.
All of the patients in the study lived within 36 selected ZIP codes within the Salt Lake, Ogden, Provo and surrounding valleys.
Rennert said he thought the research team would find that the patients would have the hemorrhage soon after a spike in PM2.5 pollution. Instead, the brain bleeds occurred between 90 and 180 days after high air pollution levels.
'Over the entire study period, recurring spikes of (the brain bleed) were often seen three to six months after PM2.5 cyclic elevations, suggesting a delayed adverse effect of PM2.5 exposure,' the study reported.
While he said that was unexpected and makes drawing connections more challenging, the researchers believe that the pollution kicks off inflammation, which weakens the blood vessel and makes it more vulnerable to hemorrhage in a process that takes some time.
When they controlled for other factors that have been 'variably linked' to aneurysm in the past, including temperature, season and barometric pressure, he said only the latter on the day of bleeding was found to be associated.
The research team plans to further study how PM2.5 impacts brain health not only locally, but in a larger geographic region and they hope to involve multiple centers in future research. They also want to understand the 'mechanisms and risks of air pollution on cerebrovascular disease more broadly,' as a news release puts it. They'll start with their theory that it's due to inflammation.
Rennert said the working theory is that the pollution kicks off inflammation that does damage, then barometric pressure somehow triggers the aneurysm to bleed. 'I would say that the barometric side is not as well understood, but that is the hypothesis.' He added that a 'long-standing body of literature shows that inflammation within an aneurysm wall is associated with its risk of rupture over time. I and others are interested in pathways to mitigate that inflammation and potentially decrease the risk of an aneurysm rupturing if you do have one.'
Ultimately, they hope people including policymakers will consider the danger of air pollution and do something about it. Among ideas they offer are giving people an incentive to use public transportation, creating stricter rules around pollution levels and dedicating more funding to environmental studies.