Here's a prediction from the World Health Organization that may surprise you: Depression will become the most common global illness during the next 20 years.
"Depression is much more common compared to some other diseases that you hear about – HIV as well as cancers," said Doctor Shekhar Saxena with the WHO's department of mental health.
There are several causes of depression. Some are environmental; others are biological. The international organization Medecins Sans Frontieres or Doctors Without Borders has taken the lead in treating depression in a slum in Rio de Janeiro.
Just driving in and out of Complexo do Alemao, or the German's Complex, you soon get the idea that while the sprawling collection of shanty towns has been quieter recently, life here is far from routine.
"I think for me one of the things that actually shocks me the most is the point to which things, because the conflict has been going on for so long and you have a complete absence of the state, at a certain point things which are shocking become normal," says Tyler Fainstat.
Fainstat currently leads the Medecins Sans Frontieres operation in Brazil, which last year began working inside Complexo do Alemao providing emergency, medical, and psychological assistance at a small community health center.
"You see young boys with enormous weapons which you would normally expect to see in the war in Iraq; and you see people selling drugs out in the open; and you see a situation where the system of governance is one which is what they call the parallel power, meaning not the state but basically run by the drug gangs," he said. "The interesting thing for me is that it's not that people ever are able to cope with it, but that it becomes normal and it becomes the reality there, and people are no longer shocked by what they see."
The conflict between drug gangs and police often puts Complexo do Alemao in the headlines, and inside the favela -- for safety reasons -- the movements of reporters were restricted to the health center.
Residents like Vivianni tell of some terrifying experiences. "There was one time with my son ... my flip-flops got caught and I had to shout to him, 'Run, run get out of here' because I couldn't get away and there were bullets flying everywhere."
Vivianni sought help for depression at the health center. While many of her problems are related to her personal situation, she says living in a conflict situation does make things worse.
"If you ask anyone here they all have a similar story, not just me," she said. "For good or bad everyone needs help regardless of whether they have depression as serious as mine or just a slight case. It's normal for people to get sad from time to time but I think everyone, especially when they have seen this type of conflict, everyone should look for help – psychological help."
The Medecins Sans Frontieres team has effectively stepped in to fill a gap left by the state. Psychologist Douglas Khayat says one area where they try to help is dealing with people afraid to talk about relatives killed by drug traffickers, or what he calls the army group.
"They cannot talk about that anywhere because if the person was killed by the army group, where they can talk? They cannot announce this to the police. They cannot access justice. That's a real problem. They can come to us and they can talk and they feel confident because we have our presence in there. We put ourselves in the same conditions as them."
Douglas says the continuing threat of violence has a real impact on the mental health of their community.
"People they start to develop a kind of permanent tension, anxiety disorders, depression. And the kids you can see have learning problems and aggressiveness. You have a whole range of symptoms which you can really connect to the social situation."
Back at the Medecins Sans Frontieres clinic, Vivianni says despite all her emotional problems and the challenges of living in such a troubled neighborhood, the counseling she receives has helped rebuild her self respect.
"Depression is a delicate disease and not very well understood. I have developed confidence which was one of the key issues for me. Because of this I can talk about my problems and I feel I have improved considerably. I learned to respect my limits. I learned all this here."
Given the scale of the problem there's a limit to what a small of team of doctors and psychologists can do. But for those they have been able to help, the work of Medecins Sans Frontieres in this troubled shanty town appears to have made a real difference.
PRI's "The World" is a one-hour, weekday radio news magazine offering a mix of news, features, interviews, and music from around the globe. "The World" is a co-production of the BBC World Service, PRI and WGBH Boston.