You've seen them sleeping on city streets and huddled over grates, or maybe in doorways: Boston's homeless. And for those who opt not to go to shelters, who sleep outside exposed, there is a term for it. It's called “sleeping rough.” And here in Massachusetts, those who “sleep rough” die at a rate of nearly three times of those living in shelters, and almost ten times the rate of the general population in Massachusetts. That's according to a new study published this week in JAMA Internal Medicine, from the American Medical Association. Dr. Jill Roncarati of Harvard's T.H. Chan School of Public Health is the lead author of the study. She spoke with WGBH All Things Considered anchor Barbara Howard about the study. The following transcript has been edited for clarity.

Barbara Howard: It shouldn't be surprising that people are going to die when they're sleeping outside. Do they freeze to death?

Jill Roncarati: No, it's not from freezing to death. It's from common causes of death - cancer and heart disease were the most common causes of death that we saw.

Howard: 53 is the mean age of death?

Roncarati: Yes, it is.

Howard: Well cancer and heart disease - is that because this population smokes more?

Roncarati: It is one reason why. We saw a lot of lung cancer, and head and neck cancer. And heart disease can also be related to substance abuse and smoking as well.

Howard: Other causes included cirrhosis of the liver and drinking issues?

Roncarati: Yes, that was another leading cause of death

Howard: There’s still substance abuse and alcoholism among those who seek shelter, but they die at a lower rate.

Roncarati: One of the reasons may be related to the rules and regulations inside a shelter. For some people, it's as simple as not being able to smoke a cigarette in the middle of the night.

Howard: Your study shows that those who sleep outside tend to be white and male.

Roncarati: In Boston, yes.

Howard: But no idea really at this point why?

Roncarati: We're not exactly sure why. That warrants further research.

Howard: What kinds of things would you like shelters to be doing?

Roncarati: I think just having an array of services available at the shelters. Having shelters with fewer rules around smoking, around drug abuse, around drinking. Maybe adopting a harm reduction model.

Howard: What does harm reduction model mean?

Roncarati: In Toronto, for example, at specific time intervals, they give people who come into the shelter a certain amount of alcohol. Almost like it was prescribed to them, to be able to drink so many ounces of alcohol over a certain amount of time.

Howard: Ten years you were tracking. You must have gotten to know the people on the street pretty well.

Roncarati: I did. I knew almost everybody who passed away during that time in the city. I directly cared for the folks that passed away. Yes, I knew them.

Howard: That must have been hard.

Roncarati: It was very hard. I remember the first person who died. I remember everything about what happened. It was a gentleman, he was very feisty, had a lot of character. He was somebody we visited almost every day. He slept outside on the waterfront, and it was during the time that the Big Dig was just about ending. And he used to think that he would be safer sleeping in between jersey barriers. And in fact, he wasn't safe sleeping there at all. One night there was a big accident that happened, and a truck rolled over on top of that area where he was sleeping. He ended up dying in the emergency room. But he was such a colorful man and still very much missed.

Howard: What was his name?

Roncarati: His name was Jack.

Howard: Well thanks for joining us, Dr. Roncarati.

Roncarati: Thank you.

Howard: That's Dr. Jill Roncarati of Harvard's T.H. Chan School of Public Health. She was the lead author on a new study out this week in the journal JAMA Internal Medicine. It shows death rates for homeless people in Boston who are living on the streets three times that of the homeless who live in shelters, and ten times the rate in the general Massachusetts population. This is All Things Considered.