Researchers have found that every third person who is diagnosed for the first time with a mood disorder had been admitted to hospital with an infection prior to the diagnosis. The study, appearing in the journal JAMA Psychiatry, is the largest of its kind, following more than 3 million Danes between 1977 and 2010. It involved researchers from Aarhus University (Denmark), the University of Copenhagen, and Johns Hopkins University.
Researcher Michael Eriksen Benr�s, from Aarhus University, says the results lend strength to the idea that the immune system is intimately linked to mental health. That notion adds another facet to the “hygiene hypothesis” that links a variety of autoimmune conditions to an inflammatory response caused by the loss of healthy bacteria in the gut.
“Our study shows that the risk of developing a mood disorder increases by 62 percent for patients who have been admitted to hospital with an infection. In other words, it looks as though the immune system is somehow involved in the development of mood disorders,” said Benr�s.
The new findings place a question mark over our understanding of the blood-brain barrier which is supposed to protect the brain. Other recent studies have identified factors, such as diet, that appear to affect the permeability of this barrier.
Benr�s believes the increased risk of mood disorders can be explained by infections penetrating the barrier. “Normally, the brain is protected by the so-called blood-brain barrier, but in the case of infections and inflammation, new research has shown that the brain can be affected on account of a more permeable blood-brain barrier,” he suggests.
“We can see that the brain is affected, whichever type of infection or autoimmune disease it is. Therefore, it is important that more research is conducted into the mechanisms which lie behind the connection between the immune system and mood disorders,” he concluded.
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