AILSA CHANG, HOST: The attacks on the World Trade Center had a lasting impact on the lives of many. Researchers studying survivors, witnesses and recovery workers say the trauma of that day increased the rates of mental illnesses like PTSD and depression. As NPR's Rhitu Chatterjee reports, many struggled with the symptoms for years.
RHITU CHATTERJEE, BYLINE: Kristina Lozano was 16 when the attacks took place just eight blocks away from her high school.
KRISTINA LOZANO: The first time the first plane hit, I was actually in homeroom, where they take attendance. And then by the time the second plane hit, I was in English class.
CHATTERJEE: She remembers the school building shaking and being hit by debris, and she remembers walking across the Manhattan Bridge with a friend afterwards, trying to get home safely.
LOZANO: By the time we had made it to the bridge, walking perhaps half way, one of the towers had finally gone down. And I never forget that - just everybody just running.
CHATTERJEE: In the weeks and months that followed, Lozano struggle to sleep and was easily startled.
LOZANO: Any little noise, honestly, that was loud, like maybe an airplane passing by - kind of being a bit paranoid.
CHATTERJEE: Paranoid, anxious and eventually depressed.
LOZANO: I began to really doubt myself, my abilities just in terms of performing in school - kind of not really caring as well. And I was just really living almost like on autopilot.
CHATTERJEE: Lozano is among many people in and around New York City who experienced symptoms of mental illness after 9/11. Dr. Sandro Galea is the dean of the School of Public Health at Boston University. But back then, he was at Columbia University and led the first long-term study of the mental health impacts of the attacks among residents of New York, New Jersey and Connecticut.
SANDRO GALEA: What we found at the beginning was about a doubling of the baseline rate of depression, post-traumatic stress disorder in the general population.
CHATTERJEE: He also found that some people were at a higher risk of having symptoms.
GALEA: Groups that had lost loved ones or had lost possessions or had been closer to the event were more likely to have post-traumatic stress disorder or depression.
CHATTERJEE: While many recovered in about six months, Galea says about a third continued to struggle over the next three years. Today, 20 years later, many are still struggling. That's according to findings from the World Trade Center Health Registry, which has continued to check in on the health of over 70,000 people. Robert Brackbill is the director of research at the registry.
ROBERT BRACKBILL: Each time we do a survey, it's between 8- and 10%, you know, that have sufficient symptoms that indicate post-traumatic stress disorder.
CHATTERJEE: And among people who were closer to the event - for example, those who worked in the towers or rescue and recovery workers - he says the rate of PTSD is even higher, about 17- to 18%. Brackbill's colleague Mark Farfel is the director of the registry.
MARK FARFEL: This disaster of 9/11 in New York City has had long-term impacts and significant impacts on both the responders and the civilian survivors.
CHATTERJEE: He says people enrolled in the registry often have more than one mental and physical health condition, making it harder for them to recover quickly.
FARFEL: So for example, PTSD often co-occurs with depression, and that magnifies the impacts of the disaster.
CHATTERJEE: But Farfel says many who sought mental health care did recover, like Kristina Lozano, the then-16-year-old who walked across Manhattan Bridge after the attacks. She says enrolling in the registry and responding to its health service opened up a door to seeking help.
LOZANO: I sought help in college, got therapy. And therapy was a huge eye-opener for me.
CHATTERJEE: An eye-opener and a path to recovery. Today, Lozano works as a life coach. With the 20th anniversary of 9/11 just around the corner, she says she feels emotional but no longer anxious or depressed.
Rhitu Chatterjee, NPR News.
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