All got a bit better, as might be expected, but those who swam with dolphins showed a significantly greater improvement, the scientists reported.

Depression was measured in two ways, using accepted scoring methods, and by each measure the dolphin group did better.

They were also less anxious, but this change did not reach statistical significance.

“The effects exerted by the animals were significantly greater than those of just the natural setting” concluded Professor Michael Reveley and Christian Antonioli. Although the patients were randomly allocated to the groups, the trial was not truly double-blind since it must have been apparent to all that some were getting a treat that others were being denied.

But the researchers tried to prevent disappointment affecting the results by giving the control group a day session with the dolphins after the study was complete.

Support for the project came from the Tursiops Society, an Italian group with which Mr Antonioli is linked, which promotes ecotourism and the value of animals to human health.

One reason for the findings could be the emotions raised by the interaction with the dolphins, the researchers said.

Three months after the study ended, both groups of patients reported a lasting improvement and did not require treatment.

Another article in the British Medical Journal claims that owning a pet is linked to health and well-being, particularly for older people and for those who are recovering from a major illness.

The psychologist June McNicholas said that research has suggested that pet ownership is linked with a reduced risk of heart disease, lower use of GP services and a lower risk of asthma and allergies in young children.

“People do not own pets specifically to enhance their health; rather, they value the relationship and the contribution their pet makes to their quality of life” the article says.

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