STATINS, aspirin, antibiotics and fish oils have been shown to curb symptoms of major depression and significantly increase the effectiveness of common antidepressants.

The findings have been hailed as the most convincing evidence yet for a link between physical inflammation and the mental illness.

Researchers in China analysed the results of 30 randomised control trials into depression where non-steroidal anti-inflammatory drugs (NSAIDs) such as aspirin or ibuprofen, omega-3 fatty acids, statins, or an antibiotic normally used to treat acne were tested alone or in combination with antidepressants.

The study, published today in the BMJ’s Journal of Neurology, Neurosurgery & Psychiatry, found “significant antidepressant effects” for all four agents when compared with a placebo. The effects were even stronger when combined with antidepressants.

Professor Alan Carson, a consultant neuropsychiatrist and academic based at Edinburgh University’s Centre for Clinical Brain Sciences, edits the journal.

He said the study is an “important piece of the jigsaw” in understanding how severe depression develops.

It comes after a string of observational studies have found elevated levels of inflammatory proteins in the blood of people suffering from major depression.

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Prof Carson said: “This is a story that’s been slowly developing on the backburner for about 20 years, but over the last five it’s become quite a hot topic. There is evidence from a range of different sources that suggest the inflammatory mechanisms in the body are relevant to the development of depressive illness.

“For example, if you have rheumatoid arthritis or something like multiple sclerosis, the rates of depression increase about eight-fold. People have never known quite how to interpret that because it might just be about being ill.

“But what has become more persuasive is that the treatment of hepatitis B has involved using immunological treatments - an interferon - and it has as a side effect really quite significant depression. You put people on this and, for a proportion, their mood just drops.”

Long-term studies, such as the Whitehall study of more than 10,000 civil servants which began 1967, have previously found a rise in inflammatory proteins among those who later developed depression, suggesting it could be used as a predictor of who is most at risk.

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Prof Carson said the theory sheds light on the physiological mechanism by which stressful experiences such as bereavement, which trigger an inflammatory response in the body, can ultimately lead to depression.

He said: “One has to be careful not to oversell it and say that’s depression all understood, but I think it’s an important piece of the jigsaw. You get false dawns in research, and people chase a hare that doesn't end up going anywhere.

"But I think there is enough strong, cumulative evidence now to say that this is probably genuine.”

A record number of people in Scotland are taking antidepressants, with prescriptions up nearly 50 per cent in a decade.

The authors of the BMJ study noted that on their own antidepressants taken alone are "often ineffective and have side effects, such as nausea, insomnia, weight gain, metabolic disorders, cardiovascular toxicity, and even suicide". 

New treatments which are safe and effective "are urgently needed", they said. 

The only adverse events reported in the anti-inflammatory trials were gestrointestinal problems, although these only occurred when statins were used.

However, the BMJ researchers said more, larger studies were needed and noted that none of the available trials had lasted beyond12 weeks, meaning long-term effectiveness could not be evaluated.

They added: "Anti-inflammatory agents show promising effects for major depressive disorder [MDD]. However, owing to the chronic course of MDD, quality of life and adverse events should be further investigated in high-quality randomised clinical trials with long-term follow up."