Then one night, distraught, he called his wife, Maria.

“I don’t know where I am,” he told her. He had driven 15 to 20 miles north of his suburban home outside Manhattan — an area he’d known for years — but suddenly needed his wife to give him directions.

Cancer, respiratory ailments, mental health conditions and musculoskeletal disorders have long been linked to work at the site of the World Trade Center attack, and medical costs for them have been covered by the World Trade Center Health Program since it was established by an act of Congress and signed into law by President Barack Obama in 2011.

Only recently, however, have scientists begun to find that cognitive impairment and dementia are also afflicting first responders at rates far higher than in the general population. The revelations are pushing physicians and advocates to be more vocal about lobbying the World Trade Center Health Program, overseen by the Centers for Disease Control and Prevention, to include dementia among illnesses covered.

“I’m hoping they will,” said Benjamin Luft, the director of a program at Stony Brook University that cares for and monitors the health of first responders. “They have a systematic process in which they evaluate the scientific data. We’ve spent a huge amount of time and effort to establish that exposure to the neurotoxins and dust could cause these problems and so should be eligible for coverage.”

Luft was the senior author of a study published this summer involving more than 5,000 first responders who have undergone regular testing for over a decade. Those with the highest exposure to the dust and potentially neurotoxic debris at the World Trade Center, he found, were over 14 times more likely than those with the lowest exposure to be diagnosed with dementia before the age of 65.

Ray Dorsey, a professor of neurology at the University of Rochester, said tiny grains of ordinary dust, called fine particulate matter, can enter the nose and reach the brain to cause damage.

“The nose is the front door to our brain,” Dorsey said. “Dust and chemicals set up shop in the smell area of our brain, then spread to the parts of the brain important for memory.”

Recent studies have found that air pollution from factories, automobiles and forest fires can all increase the risk of dementia. “And you couldn’t get worse air pollution than being at that World Trade Center site,” Dorsey said.

On the morning of 9/11, Beyrer was stationed at a firearms training center in the Bronx. Within minutes of the first plane flying into the World Trade Center, he and other officers set off in a van, arriving before either of the buildings had collapsed.

“We were the only guys at that time who had the long guns,” he recalled. Told to station himself a couple of blocks away to provide security, he was enveloped in white-out conditions when the first building fell.

“It was terrible,” he said. “It was completely dark with dust.”

After some 48 hours on and around the mound of debris without a mask or any other protective equipment, Beyrer returned home covered in white soot.

“He took a shower and told me to take those clothes, throw them outside, get rid of them,” Maria Beyrer said. “Then he got dressed and went back out. He was there for six months, 12 hours a day.”

Although light face masks were eventually distributed, he said, “they didn’t really help. I guess they were better than nothing.”

Told by Luft that his months of exposure probably played a role in his cognitive symptoms, the Beyrers have made accommodations. She does the driving, for instance, when they’re together.

But whether it was dust alone that increased the risk of dementia in first responders, or harmful chemicals that piggy-backed on the dust, is impossible to disentangle, at least for now, said a co-author of the study led by Luft, which was published in the journal JAMA Network Open.

“We focused on dust in this study because that is what people could see,” said Sean Clouston, the director of research and a professor in the department of family, population and preventive medicine at Stony Brook Medicine. “They knew if they had or had not been exposed to it. But there were fumes from chemicals, jet engine fuel, burning computers, asbestos, heavy metals. There’s a whole bucket of things people were exposed to.”

The longer responders spent on the site, and the less protective gear they wore, the higher their risk of developing early dementia, the study found. Using a metric called “person-years” (by multiplying the number of responders times the amount of time they spent at the site), they found that for those who had the lowest exposure, the incidence rate of dementia was 2.95 per 1,000 person-years. But even those who had “mild” exposure had a greatly increased risk: 12.16 per 1,000 person-years.

The next highest level of exposure, labeled “moderate,” carried only slightly more risk, at 16.53 per 1,000 person-years. Those with “high” exposure, however, had an incidence rate of 30.09 per 1,000 person-years, while responders with “severe” exposure had a rate of 42.37 per 1,000 person-years.

“The fact that they’re showing a dose-response effect makes me more confident in the results,” said Caroline Tanner, a neurologist at the University of California at San Francisco who was not involved in the study. “It’s usually very hard to know exactly how much exposure people have to fine particulate matter. It’s remarkable that they could measure it and show a higher risk of dementia as the exposure went up. It’s an extremely well-done study.”

An earlier study by Clouston and Luft offered a possible explanation for why exposure to the World Trade Center site would be linked to dementia. In a paper they published last year in the journal Molecular Neurobiology, they reported that the longer responders spent at the site, the more inflammation they had in their hippocampus (the seahorse-shaped brain area that plays a crucial role in memory) and cerebral white matter (the nerve fibers that connect neurons to each other).

The years it has taken for cognitive deficits to develop among responders is one reason that the World Trade Center Health Program, overseen by the CDC, does not cover dementia or milder cognitive disorders.

Anthony Gardner, spokesman for the World Trade Center Health Program, said in a statement that the program’s leaders are aware of the study by Clouston and Luft and are reviewing the findings. In fact, he said, the program partly funded it.

But, he said, the program has a high scientific standard for adding any condition to the list of those covered by the program. “Meeting this standard generally requires consistent findings among several high-quality large studies of persons representing different groups,” he said. “To date, the program has not received a valid petition to add dementia or other cognitive conditions to the list of WTC-related health conditions.”

Benjamin Chevat, the executive director of 911 Health Watch, an independent group that monitors World Trade Center programs and advocates for changes when necessary, said the study of dementia risk will need to be replicated by other researchers to meet the requirements of the federal program.

“It would be great if this condition could be added tomorrow, but regretfully science does not work at the speed we would like,” he said.

Senate Majority Leader Charles E. Schumer (D-N.Y.) said that he helped to establish and fund the World Trade Center program so responders and survivors get the care they need. “We pushed for robust research funding for the program and wrote a process that allows for the program to follow the research to add conditions that are supported by scientific evidence,” he said. “I very much support this process and the research running as quickly as possible.”

Sen. Kirsten Gillibrand (D-N.Y.) said the study’s finding of a 14-fold increased risk of early-onset dementia is “extremely alarming.”

“It’s essential that the CDC and medical community analyze this further in order to determine whether to add it to the list of conditions covered by the [World Trade Center Health Program],” she said.

Regardless of whether dementia and other cognitive issues are recognized by the program, Tanner said, an important lesson can already be drawn from the study of dementia in World Trade Center responders.

“The big take-home from this paper is that people who used personal protective equipment were protected from the worst effects,” she said. “That should apply to people in any industry where they run the risk of exposure to fine particulate matter. It applies certainly to firefighters. And for those of us who live downwind from a forest fire, maybe we should be asking about public health measures that can protect people when we know the air quality is poor.”

Beyrer’s cognitive symptoms, which have stabilized in the past couple of years, are hardly the only effects he has lived with since serving at Ground Zero. He suffered for years with lung, stomach and sleep problems, and half of his left lung had to be removed because of a noncancerous growth, which doctors told him was probably due to something he breathed in at the site. But despite it all, Maria insists they are among the lucky families who sent a loved one to respond to the World Trade Center attack.

“He still has problems sleeping,” she said. “But we are one of the fortunate ones. We’re able to manage. Whereas people have lost their parents, lost their children.”

As Tom Beyrer sees it, “There are times when it’s not okay. But I did what I had to do. Me and my friends. That was our job.”