There even seems to be a "dose-response" relationship: the more urban your environment, the more likely it is to induce serious psychiatric illnesses.
So it's worse for your mental health to live in the inner city compared with the suburbs which, in turn, are worse than a rural location.
But why? The most intriguing theory is that alienation from nature induces psychological dysfunction. This "biophilia hypothesis" received a substantial fillip when a report in the British Medical Journal showed that seriously depressed patients improved remarkably when they swam with dolphins. These patients had stopped their antidepressants for a month before starting the "dolphin therapy". The study, which was conducted in Honduras but run by Professor Michael Reveley of the University of Leicester, found that interacting with animals not only produced dramatic cures of depressive symptoms in three-quarters of the subjects, but that they took effect in less than two weeks, substantially quicker than the one month it usually takes antidepressants to start working.
The biophilia hypothesis can be traced back to Erich Fromm, an influential left-wing psychoanalyst who came to prominence in the 1950s. He argued that an unconscious driving force in modern western societies was a desire to compensate for our sense of a lack of "authentic self". As a result, we appear to identify with the lifeless, and are superficially attracted to whatever is devoid of life - that is, objects rather than living creatures or plants. In 1976 he published a remarkably prescient book, To Have or To Be? Modern capitalism, he wrote, forces us to choose between "having", which derives meaning in life from material possessions, and "being", which is rooted in "love" and "shared experience". He foresaw that the dominance of "having" was driving the world to the edge of not just ecological, but social and psychological disaster. He prophesied that only a turn to "being" could save us from ourselves and coined the term "biophilia" to describe this new orientation towards a love of life as embodied in nature.
Dr Raj Persaud is consultant psychiatrist at the Maudsley Hospital in south London and Gresham professor for public understanding of psychiatry. His latest book is The Motivated Mind (Bantam Press). Email: firstname.lastname@example.org