A device that sends an electric current into nerve fibres found in the ears could help millions of people with depression.

The gadget, which can be used at home, works by transmitting mild currents through clips fixed to skin on the ears.

This stimulates a nerve connected to an area of the brain that regulates mood. Research shows that using the device for an hour a day can help patients who have not responded to anti-depressant drugs.

The current generated is too low to cause discomfort but enough to stimulate tiny branches of the vagus nerve found in the auricular concha - the shell-like cavity in the middle of the ear that leads to the ear canal. Experts at the China Academy of Medical Sciences in Beijing studied 49 patients suffering from mild to moderate depression.

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The patients were taken off their anti-depressants two weeks before the test so as not to skew the findings. They were then given a hand-held device to send a mild current through clips attached to both ears twice a day for a month.

The results, published in the journal Biological Psychiatry, showed zapping the vagus nerve significantly reduced patients' scores on the Hamilton Rating Scale - a system used by psychiatrists to measure the severity of a patient's depression.

Anything between zero and seven is considered normal, while 20 or over is classed as moderate to severe. The treatment slashed average scores from 28.50 to 15.

In a report on the findings, researchers said: 'We found this type of vagus nerve stimulation can significantly reduce the severity of depression in patients."

Psychiatrist Professor Danny Smith, of Glasgow University, welcomed the findings, saying: "This looks potentially promising. It's non-invasive and could benefit large numbers of people. But this is a small trial and more research will be needed."