Why millions of Americans find it hard to have a nice day

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Americans are not only the fattest Westerners on earth. They are also among the most depressed. Could the size of their girth have some bearing on their mental state? One in six adult Americans will suffer a serious episode of depression at some time in their lives, according to a survey by the National Institute of Mental Health in Bethesda, Maryland.

One in 15 - that is 13 million people in the US - have had serious depression within the past year lasting, on average, for four months.

The burden of misery has a huge impact on the US economy costing employers $44bn (£26bn) in lost production. That compares to only $13bn lost for those without depression, according to a separate study by the Outcomes Research Institute at Geisinger Health Systems, Danville, Pennsylvania.

Both studies are published in the Journal of the American Medical Association. Researchers from the National Institute of Mental Health found that only half of those who had depression in the past year had received treatment and in only half of them had the treatment been adequate. The survey was based on interviews with 9,000 people across the US.

The researchers found depression was twice as common in women as in men, echoing a finding from a 2001 survey in five countries in Europe. That survey showed the prevalence of depression varied hugely, with rates more than six times higher in Liverpool, at 17.1 per cent than in Santander, northern Spain (2.6 per cent).

The European study, published in the British Journal of Psychiatry, provided a snapshot of the level of depression at the time the research was carried out. The variation was widest among women and narrowest among men. Professor Christopher Dowrick, an author of the original study who has conducted further research to be published later this year, said: "It has a lot to do with the amount of social support women receive. The important factor seems to be whether they have people they can turn to when things are difficult.

He said: "One of the many good things about being in Santander, compared to Liverpool, is that there is a much stronger extended family and social support."

The American researchers from the Outcomes Research Institute found that fewer than 30 per cent of people with depression used anti-depressants and concluded that "there may be cost effective opportunities for improving depression-related outcomes in the US workforce". However, the study was funded and in part designed by Eli Lilly, makers of Prozac.

In Britain, Professor Dowrick said: "There are a lot of drivers in the system in favour of a diagnosis of depression, including the drug companies, and I think it is questionable whether the increase in diagnoses is benefiting patients."