The research "brings to attention an unrecognised problem," said Dr. Alexander Neumeister, director of the molecular imaging program for anxiety and mood disorders at New York University School of Medicine.
Crucial to treat both problems
It's crucial to treat both PTSD and diabetes when they're interconnected in women, he said. Otherwise, "you can try to treat diabetes as much as you want, but you'll never be fully successful," he added.
PTSD is an anxiety disorder that develops after living through or witnessing a dangerous event. People with the disorder may feel intense stress, suffer from flashbacks or experience a "fight or flight" response when there's no apparent danger.
It's estimated that one in 10 U.S. women will develop PTSD in their lifetime, with potentially severe effects, according to the study.
"In the past few years, there has been an increasing attention to PTSD as not only a mental disorder but one that also has very profound effects on brain and body function," said Neumeister, who wasn't involved in the new study.
Among other things, PTSD sufferers gain more weight and have an increased risk of cardiac disease compared to other people, he said.
The new study followed 49,739 female nurses from 1989 to 2008- aged 24 to 42 at the beginning- and tracked weight, smoking, exposure to trauma, PTSD symptoms and type 2 diabetes.
People with type 2 diabetes have higher than normal blood sugar levels. Untreated, the disease can cause serious problems such as blindness or kidney damage.
Over the course of the study, more than 3,000 of the nurses, or 6 percent, developed type 2 diabetes, which is linked to being overweight and sedentary.
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Twice as likely to develop diabetes
Those with the most PTSD symptoms were almost twice as likely to develop diabetes as those without PTSD, said study co-author Karestan Koenen, professor of epidemiology at Columbia University Mailman School of Public Health in New York City.
The study doesn't prove that PTSD directly causes diabetes, although Koenen said the study's design allows the researchers to "know that PTSD came before type 2 diabetes."
Since PTSD disrupts various systems in the body, such as those that manage stress hormones, "it may be that something about PTSD changes women's biology and increases risk" of diabetes, she said.
Use of antidepressants and higher body weight accounted for almost half the increased risk, Koenen said.
"The antidepressant finding was surprising because as far as we know, no one has shown it before," she said. "Much more research needs to be done to determine what the finding means."
Obesity explains some, but not all, of the relationship, she said.
Neumeister said there could be a connection from PTSD to overeating to diabetes, but he believes the situation is more complex than it sounds.
"Many PTSD patients are on the overweight end of the spectrum, and that's true for both men and women," he said. "We don't understand this link." Some factor, perhaps genetic, could make people more prone to both conditions, he said.
Read: 1 in 4 stroke survivors suffers from PTSD, study finds
What about men?
"Our findings are consistent with findings for male veterans," Koenen said. "Studies need to be done in men in the general population, but based on these data we would expect findings to be similar."
For now, Neumeister said doctors should pay more attention to the possible causes of diabetes.
"Physicians in general don't ask enough questions, but when they do, they forget to ask questions about psychological factors that potentially contribute to medical problems."
The study appears in the Jan. 7 issue of JAMA Psychiatry.
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