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A recent study published in JAMA Network Open has found that individuals who responded to the September 11, 2001, World Trade Center attacks and were heavily exposed to dust and debris were significantly more likely to develop dementia before the age of 65. The more intense the exposure—particularly for those working directly on the debris pile without protective equipment—the greater the risk. Responders with minimal dust exposure or those who wore personal protective gear had much lower rates of dementia.
The researchers wanted to understand whether the type and severity of exposure during the World Trade Center cleanup were linked to long-term brain health. Previous studies had identified signs of cognitive decline and brain changes in responders, including memory issues and brain shrinkage, which are often early signs of dementia. Although dementia before age 65 is rare in the general population, the team suspected that the combination of extreme environmental hazards and lack of protection may have increased the risk for this group. They also wanted to see whether wearing protective gear could reduce that risk.
“Over the past ten years, there has been increasing recognition that fine particulate matter and airborne pollutants can enter the brain,” said study author Sean Clouston, the director of Public Health Research and a professor at Stony Brook University. “At the same time, we have been finding that WTC responders are suffering from high levels of cognitive impairment that is unusual for their age and educational background. This study was the first to try to explain that difference and link it to the types of exposures that responders reported when they were on-site.”
To explore this, the researchers analyzed data from 5,010 responders who were under 60 years old at the time of their first cognitive assessment. All participants had worked or volunteered at the World Trade Center site during the response and recovery efforts between September 2001 and July 2002. They were tracked over a period of up to 8 years, starting in 2014, and underwent repeated cognitive assessments. Participants were excluded if they had previous neurological conditions, traumatic brain injuries during 9/11 work, or existing dementia at the beginning of the study.
Researchers collected detailed information about the responders’ activities at the disaster site, including where they worked, what tasks they performed, and whether they were exposed to dust, smoke, or fumes. They also recorded whether the responders used personal protective equipment such as masks or suits.
Based on this information, the research team developed a five-level scale to rate each person’s exposure severity, from low to severe. People in the lowest group either wore protective gear or reported no direct contact with dust, while those in the highest group worked in the most hazardous conditions—like digging through rubble on the debris pile—without consistent use of protective equipment.
To measure dementia, the researchers used standardized tests of memory, problem-solving, and attention. Participants had to show consistent declines across multiple assessments, along with signs of difficulty managing daily tasks, for a dementia diagnosis to be made. The diagnosis was also cross-checked to rule out other medical causes. The team adjusted their findings for other factors that could influence dementia risk, such as age, education level, cardiovascular health, smoking and drinking history, and genetic predisposition.
During the follow-up period, 228 responders developed dementia before turning 65. While the general population sees about 1 to 2 cases of early-onset dementia per 1,000 person-years, the average among these responders was about 14.5 cases. The rate varied greatly depending on exposure severity. In the lowest exposure group, only about 3 cases occurred per 1,000 person-years. But in the most severely exposed group, the rate rose to over 42 per 1,000 person-years.
Even after adjusting for age, medical history, and other factors, the link between exposure severity and dementia remained strong. Responders in the highest exposure group were nearly ten times more likely to develop dementia than those in the lowest group. The risk increased steadily across each step of the exposure scale. Importantly, wearing protective gear appeared to significantly reduce the likelihood of developing dementia, even among those who worked in hazardous conditions.
“I was somewhat surprised at how well protected some people were,” Clouston told PsyPost. “For example, we found that people who reported working in personalized protective equipment had rates of early-onset dementia that were similar to what you see in the general population.”
For the general public, these findings serve as a warning about the potential dangers of breathing in toxic dust and debris.
“Hopefully, the average person is not exposed to these types of severe and traumatic exposures,” Clouston explained. “However, one point that is important to the average person may be that some things that you do without thinking, like cleaning up debris and ash after a wildfire in your neighborhood, may be more dangerous than you think. Thankfully, this work and others suggests that wearing protective gear can have both a short-term benefit in causing less lung damage, and a long-term benefit in protecting against dementia before age 65 years.”
To confirm their results, the researchers ran additional analyses using machine learning to classify exposure risk, and the outcomes remained consistent. They also tested whether the results held up in smaller groups with genetic data, in people who had recovered from COVID-19, or when taking into account missing or incomplete data. Across all scenarios, the link between higher exposure and higher dementia risk remained.
However, the study does have limitations. The sample was drawn from a group of responders who participated in a federal health monitoring program, and nearly all were English-speaking, which may limit how broadly the results can be applied. Also, exposure levels were based on self-reports collected years after the fact, and there is currently no medical test to measure how much dust or chemicals an individual actually inhaled at the site.
“We don’t yet know exactly what the causal mechanisms are, so that means we can’t say whether it is due to a specific exposure at the WTC sites or if it’s a general exposure,” Clouston noted. “That means that we don’t know if the WTC site is dangerous because a jet burned or because there was just fine air pollution in the air in general. Future research is still needed to answer that question, but it’s important to know when trying to understand risk from future exposures.”
“We still need to better understand whether WTC exposures result in a known condition or in a new disease. We also need to better understand both the point of entry and the active agent at the exposure event.”
The study, “Incidence of Dementia Before Age 65 Years Among World Trade Center Attack Responders,” was authored by Sean A. P. Clouston, Frank D. Mann, Jaymie Meliker, Pei-Fen Kuan, Roman Kotov, Lauren L. Richmond, Tesleem Babalola, Minos Kritikos, Yuan Yang, Melissa A. Carr, and Benjamin J. Luft.
