Where is the world's most stressful city?

Research has shown that city-living has been linked to depression and anxiety - but what is it, exactly, that makes urban life so stressful? And what can be done to make the world's cities more habitable?

"Sitting constantly in dilapidated cars wrecks their spines, and the ceaseless shouting that goes on in the streets of Cairo destroys their nervous systems," Khaled Al Khamissi wrote in his 2007 book Taxi, a collection of conversations with 58 of Cairo's 80,000 taxi drivers. "The endless heavy traffic drains them psychologically and the struggle to make a living " strains the sinews of their bodies."

It's a depressing portrait of life in Egypt's bustling capital. Could it be that Cairo, the "mother of the world", is one of the most stressful places on the planet? Or does it all depend on how you make your living there?