Stress does bad things to the heart. New studies have found higher rates of cardiac problems in veterans with PTSD, New Orleans residents six years after Hurricane Katrina and Greeks struggling through that country's financial turmoil.

Disasters and prolonged stress can raise "fight or flight" hormones that affect blood pressure, blood sugar and other things in ways that make heart trouble more likely, doctors say. They also provoke anger and helplessness and spur heart-harming behaviors like eating or drinking too much.

"We're starting to connect emotions with cardiovascular risk markers" and the new research adds evidence of a link, said Dr. Nieca Goldberg, a cardiologist at NYU Langone Medical Center and an American Heart Association spokeswoman.

She had no role in the studies, which were discussed Sunday at an American College of Cardiology conference in San Francisco.

The largest, involving 207,954 veterans in California and Nevada ages 46 to 74, compared those with PTSD, or post-traumatic stress disorder, to those without it. They were free of major heart disease and diabetes when researchers checked their Veterans Administration medical records from 2009 and 2010.

Checked again about two years later, 35 percent of those with PTSD but only 19 percent of those without it had developed insulin resistance, which can lead to diabetes and hardening of the arteries.

Doctors also saw higher rates of metabolic syndrome — a collection of heart disease risk factors that include high body fat, cholesterol, blood pressure and blood sugar levels. About 53 percent of veterans with PTSD but only 37 percent of those without it had several of these symptoms.

The numbers are estimates and are not as important as the trend — more heart risk with more stress, said one study leader, Dr. Ramin Ebrahimi, a cardiologist at the Greater Los Angeles VA Medical Center and a professor at UCLA. It shows that PTSD can cause physical symptoms, not just the mental ones commonly associated with it.

"Twenty or 30 years ago PTSD was a term reserved for combat veterans. We have come to realize now that PTSD is actually a much more common disorder and it can happen in veterans who did not undergo combat but had a very traumatic experience" such as losing a friend, he said.

That goes for others who suffer trauma such as being raped, robbed at gunpoint or in a serious accident, he said. Nearly 8 million Americans have PTSD, the National Institute of Mental Health estimates.

They include survivors of Hurricane Katrina. Tulane Medical Center doctors led a study of their hospital's patients that suggests heart attack incidence is three times higher in New Orleans than it was in the two years before the 2005 storm.

Heart attacks made up 2.4 percent of admissions in the six years after the storm compared to just 0.7 percent before it. The post-storm patients were more likely to be unemployed or uninsured, to smoke, and to have depression, anxiety or high cholesterol, resarchers found.

 A third study found that heart attacks rose sharply in the Messinia area of southwestern Greece since January 2008, the start of that country's financial crisis. Researchers compared medical records of more than 22,000 patients admitted to the General Hospital of Kalamata — the only hospital with a cardiology department in the region.

There were 1,084 heart attacks in the four years after the crisis began compared to 841 in the four years before it, even though the population and its demographics remained the same.

Heart attack incidence rose 40 percent among women, who have higher unemployment rates than men and tend to be more responsible for child care — a double burden of stress, said the lead researcher, Dr. Emmanouil Makaris.

Chris Graythen / Getty Images

LAPLACE, LA - AUGUST 29: Rescue workers transport residents trapped by rising water from Hurricane Isaac in the River Forest subdivision on August 29, 2012 in LaPlace, Louisiana. The large Level 1 hurricane slowly moved across southeast Louisiana, dumping huge amounts of rain and knocking out power to Louisianans in scattered parts of the state. (Photo by Chris Graythen/Getty Images)

It’s the question so many of us have while watching news coverage of a hurricane or tropical storm like Isaac: Who are these people who don’t leave home even as an angry storm is advancing – and what are they thinking?!

The short answer: For some, the up-and-leaving idea isn’t as easy as it sounds to those of us watching from a safe and dry distance. Actually, a 2009 article published in the journal Psychological Science sought to examine the reasons some people won’t evacuate, despite the urging or even mandates of city and state officials, by asking a group who would know: Hurricane Katrina survivors who weathered the storm at home.

“It seems like asking ‘Why didn't people leave?’ presumes that that's the best option for everyone to make,” says Hilary Bergsieker, who worked with Nicole Stephens, now of Northwestern University, on the study. The fact is, many people lack the resources to escape. Having no money, no mode of transportation and no friends or family in safe places means no choice but to weather the storm. 

In the case of Katrina, those who evacuated before the storm hit were mostly white, mostly middle class; on the other hand, those who stayed were mostly black, mostly working class. The “leavers,” as the Psychological Science paper terms those who fled before the storm, had privileges that they probably took for granted: more education, more money, reliable access to transportation, social networks that extended farther away from the hurricane-hit area, and more access to news reports to warn them of the storm’s severity.

"Middle- and upper-class Americans are more geographically mobile and have more experience traveling nationally and internationally. I think that the familiarity with moving or traveling would contribute to the ability to make a plan for how to evacuate,” says Stephens, who is an assistant professor at the Kellogg School of Management at Northwestern. "On the other hand, if you have spent most of your life in the same community, then you would likely feel more attachment to your home and feel less comfortable as well as less equipped to quickly uproot yourself in response to evacuation orders." 

Even if a person does have the resources at hand to make an escape, it might be unthinkable to leave behind a tightknit community like those you’d find in many parts of coastal Louisiana and Mississippi.

Slideshow: Isaac moves inland

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A downgraded Isaac floods coastal communities and forces new evacuations, but levees still hold.

Launch slideshow

“There's sort of the physical resources factor, but there's also the psychological factors. That's your world; that's all you know,” says Bergsieker, who is now an assistant professor of psychology at the University of Waterloo in Ontario, Canada. And, as the thinking goes, if your neighbor tells you he’s staying, then you might stay, too – after all, if something happened to him, who would be there to take care of him if you leave? Some of the 79 Katrina survivors interviewed in the 2009 study did have the resources to go, but they didn’t have the heart to leave.

Ariella Cohen moved to New Orleans in 2007, so she wasn’t there when Katrina hit. But in 2008, when Hurricane Gustav started moving toward her city, she decided to stick it out, despite the city's mandatory evacuation order.

“I had friends who had stayed through Katrina, and I had heard all their stories about it, and so I think I also inherited all their jadedness, too,” says Cohen, who wrote about her Gustav close encounter for the website Next American City. “You know, just kind of that New Orleanian attitude of, ‘Whatever! We’re going to stay here. Do you want another beer?’” On a more serious note, her rationale for staying was: 'I’m young, I’m able-bodied and relatively fit. What if someone older and weaker needs me?' “I was, like, 27 at the time, so I was young and strong, and I would be able to help people if the time came,” says Choen, now 31, who lives in Philadelphia, where she works as an editor for the same site that published her 2008 essay.

Mistrust of outsiders – as in, people who aren’t from your community who are claiming to know more than you do about your own home by telling you to leave it – can play a part, too. “This is where you've always been your whole life, and suddenly people on the radio are telling you you have to leave? That may seem like a much more dangerous choice than to stay with people from your church, or people from your block,” Bergsieker says.

Besides, those who live in a hurricane-prone area hear these warnings all the time. It can be easy to stay in denial about an impending storm’s ferocity when the local news station has cried “hurricane” so many times before. (Sometimes that tack pans out: In Cohen’s lucky case, Gustav bypassed New Orleans.)

Read this far and still think anyone who’d ignore a hurricane evacuation mandate must be just plain crazy? That sounds about right. A second piece of the study asked both Katrina relief workers and regular folks to describe the “leavers” and the “stayers” in three words. The leavers were called independent, self-reliant, responsible, hard-working, conscientious. The stayers, on the other hand, were described mostly in negative terms: Passive. Crazy. Lazy. Irresponsible. Careless. Hopeless. 

Take a dive into the comments section on this NBCNews.com story on Isaac, and the sentiment sounds about the same. Like this one: "What part of MANDATORY EVACUATION do these people NOT UNDERSTAND!" (Bold text and gratuitous use of the caps-lock key are the commenter's own.) Or this: "You were told to evacuate! Now you should be on your own and not expect others to put themselves in harms way!"

In the study, relief workers and others alike acknowledged that many of the stayers might have lacked the financial resources to leave, and yet they still used mostly negative terms to describe them. That disconnect is what Stephens was interested in exploring in the 2009 article, which argues that maybe people who “choose” to dig in their heels and remain in their communities, even when a storm’s a-comin’, actually don’t feel like they ever had a choice. Whether for financial or psychological motives, they're staying. 

 “In retrospect, definitely I was a bit naïve. Natural disasters don’t go by the logic of human psychology,” Cohen acknowledges. “I think that there’s a lot of it that’s hard to conceive – like, it’s hard to conceive of your own death, it’s difficult to conceive of natural disaster. It just seemed unbelievable that another storm could hit the city hard. And so I stayed.”

Keep up with NBCNews.com health editor Melissa Dahl on Twitter.

Related stories:

• More evacuations as Isaac dumps rain on Gulf
• The long road back from Katrina
• Horrible memories for New Orleanians