Depression is now the “leading cause of disability worldwide”, a new report has revealed.

The research, published by the World Health Organisation (WHO), found that more than four per cent of the world’s population suffers from depression, costing the global economy around £1 trillion a year.

It says that depression, a mental illness which affects people of all ages, can often leave people unable to cope at work, leading to a loss of productivity.

Dr Dan Chisholm, of WHO’s Department of Mental Health and Substance Abuse, said: “Depression is the single largest contributor to years lived with disability. So it’s the top cause of disability in the world today.”

Their study further found that depression is 1.5 times more common among women than men, and is more likely to affect young people, pregnant or post-partum women, or the elderly.

Dr Chisholm said: “The pressures on today’s youth are like no other generation perhaps.

“Another target group is women who are pregnant or have just given birth. Depression around that period is actually extremely common, around 15 per cent of women will suffer not just ‘the blues’, but a diagnosable case of depression.”

For those in retirement, he says, losing responsibility of a job or the death of a partner makes elderly people more susceptible to physical diseases and mental disorders such as depression.

WHO has recently launched a campaign to tackle the stigma and misconceptions surround depression, called “Depression: Let’s Talk”.

“We feel that is a key first step, that if we want to bring mental health, depression and other mental disorders out of the shadows, we need to be able to talk about it,” Dr Chisholm said.