Around one in 13 people in Britain suffers from anxiety or depression and last year the NHS issued 64.7 million prescriptions for antidepressants, double the amount given out a decade ago.
Current treatment is largely centred around restoring mood-boosting chemicals in the brain, such as serotonin, but experts now think an overactive immune system triggers inflammation throughout the entire body, sparking feelings of hopelessness, unhappiness and fatigue.
It may be a symptom of the immune system failing to switch off after a trauma or illness, and is a similar to the low mood people often experience when they are fighting a virus, like flu.
A raft of recent papers, and unexpected results from clinical trials, have shown that treating inflammation seems to alleviate depression.
Likewise when doctors give drugs to boost the immune system to fight illness it is often accompanied by depressive mood – in the same way as how many people feel down after a vaccination.
Professor Ed Bullmore, Head of the Department of Psychiatry at the University of Cambridge, believes a new field of ‘immuno-neurology’ is on the horizon.
“It’s pretty clear that inflammation can cause depression,” he told a briefing in London to coincide with this week’s Academy of Medical Sciences FORUM annual lecture which has brought together government the NHS and academics to discuss the issue.
“In relation to mood, beyond reasonable doubt, there is a very robust association between inflammation and depressive symptoms. We give people a vaccination and they will become depressed. Vaccine clinics could always predict it, but they could never explain it.
“The question is does the inflammation drive the depression or vice versa or is it just a coincidence?
“In experimental medicine studies if you treat a healthy individual with an inflammatory drug, like interferon, a substantial percentage of those people will become depressed. So we think there is good enough evidence for a causal effect.”
“There is evidence to suggest it should work,” added Prof Bullmore.
The immune system triggers an inflammatory response when it feels it is under threat, sparking wide-ranging changes in the body such as increasing red blood cells, in anticipation that it may need to heal a wound soon.
Scientists believe that associated depression may have brought an evolutionary benefit to our ancestors. If an ill or wounded tribal member became depressed and withdrawn it would prevent a disease being passed on.
However a link has taken so long to establish because until recently scientists believed the brain was entirely cut off from the immune system, trapped behind a ‘Berlin Wall’ known as the blood brain barrier.
But recent studies have shown that nerve cells in the brain are linked to immune function and one can have an impact on the other. Around 60 per cent of people referred to cardiologists with chest pain do not have a heart problem but are suffering from anxiety.
Figures also show that around 30 per cent of people suffering from inflammatory diseases such as rheumatoid arthritis are depressed – more than four times higher than the normal population.
Likewise people who are depressed after a heart attack are much more likely to suffer a second one, while the lifespan for people with cancer is hugely reduced for people with mental illness.
“You can’t separate the mind from the body,” said Prof Sir Robert Lechler, President of the Academy of Medical Sciences.
“The immune system does produce behaviour. You’re not just a little bit miserable if you’ve got a long term condition, there is a real mechanistic connection between the mind, the nervous system and the immune system.
“Our model of healthcare is outdated. We have a separation. Mental healthcare is delivered by mental health professionals, psychiatrists, mental health nurses and so on, often in separate premises from where physical health care is delivered and that is simply wrong and we need to find ways to ever more closely integrate and train amphibious healthcare professionals who can straddle this divide.”
Research has also shown that people who have suffered severe emotional trauma in their past have inflammatory markers in their body, suggesting their immune system is constantly firing, as if always on guard against abuse.