Nearly a quarter of a century after the 9/11 attacks in New York City, first responders continue to face steep health consequences for their exposure to particulate matter in the aftermath of the World Trade Center’s collapse. More than 10,000 people who were in the area have been diagnosed with cancer, with an incidence 30% higher than in the general population, and more first responders have died from long-term health issues associated with the collapse than during the attack.
The toll continues to grow. A new study published on Wednesday in JAMA Network Open found a significant increase in early-onset dementia among 9/11 first responders compared to the general population.
The study enrolled about 5,000 9/11 responders who were younger than 60 at the start of the study, and who didn’t have dementia symptoms or other neurological or cardiovascular conditions. Researchers followed them for an average of five years between 2014 and 2023 — and in that time, 228 responders were diagnosed with dementia.
Incidence of dementia among people under 65 is rare, occurring in 1.2 people per 1,000 between the age of 30 and 64. But the study group’s rate of early-onset dementia is nearly 40 times higher. “We would have expected one to two, maybe three cases at the very most, and so seeing several hundreds was something of a surprise,” said Sean Clouston, an epidemiologist in the Department of Family, Population, and Preventive Medicine at Stony Brook University and the paper’s lead author.
The high incidence is even more striking, he said, because most of the people involved in the cohort were highly educated, and performing highly skilled jobs — a group that tends to see lower incidence of dementia compared to the general population.
The findings align with recent research associating exposure to particulate matter, a type of air pollution containing debris and liquid particles so small that they can be inhaled, with greater risk of dementia. They also revealed a correlation between the level of a responder’s exposure to dust and debris and the likelihood of a dementia diagnosis.
At the beginning of the study, responders evaluated the severity of their exposure to particulate matter on a detailed questionnaire. It assessed their exposure to fine particulate dust and potentially neurotoxic debris (based on the location and type of work they conducted), duration of work, and the use of personal protective equipment. Based on their responses, researchers divided their exposure into five categories of increasing severity.
The study found dementia diagnoses increased in proportion with the severity of the exposure. Of 89 respondents with severe exposure, 12 were diagnosed with dementia. But only three out of 342 respondents with low exposure — including responders who used protective equipment such as hazmat suits and respirators — received diagnoses.
The lower incidence of dementia in responders wearing PPE has important real-life implications, said Roberto Lucchini, a professor of occupational and environmental health sciences at the Robert Stempel College of Public Health and Social Work at Florida International University, who was not involved in the study.
“We have situations of exposure to these kinds of toxic substances and all these hazards in a variety of situations, including natural disasters … or destruction of buildings — collapses or demolitions or earthquakes,” said Lucchini, who studies post-9/11 particulate matter exposure in Florida, where he follows retired responders who have moved to the area from New York and New Jersey. “Situations where you can have that type of exposure are unfortunately quite frequent from a global perspective,” he said.
The findings support a growing body of evidence on the effects of air pollution and dust on the risk of neurodegenerative diseases, and could provide support for recommended interventions and precautions. “For the most part, we don’t give guidance to people to wear masks on the job because they might eventually get dementia,” said Clouston. “If you’re doing a job with a lot of dust exposure, maybe that should be some of the consideration.”
The mechanisms that link exposure to dementia need further investigation, said Clouston. “There’s still more research to be done about the precise mechanism,” he said. “But the current theory is that the dust or the neurotoxic chemicals have some way to enter the brain.”
There are limits to the study, the main one being that its measures of exposure are based on what people remember doing and where — memories that can be incomplete and subject to recall bias. In more recent situations, such as a condo collapse in Surfside, Florida, researchers have been able to assess the level of exposure directly, said Lucchini. But this was not possible on 9/11.
On the other hand, he pointed out, a study on the World Trade Center’s first responders can be particularly valuable when researchers assess the impact of events that include building collapses, combustion, and challenging first response circumstances. “We can expand this conversation, unfortunately, to any conflict like Gaza or Ukraine, where you also have demolitions, you have chemicals, you have a lot of hazards for human health,” said Lucchini. “We know a lot about that from the military, because they do a lot of studies to protect the soldiers. But there’s almost no study about the general population impacted by exposure in the war zones.”