Yet again research indicates a strong link between physical and mental health.

A comprehensive new study now shows that people who have had an autoimmune disease are 45 percent more likely to develop depressions and other conditions.

Similarly, the risk of developing a mental disorder is 62 percent higher than in the general population if you have suffered a serious infection.

Researchers used massive register

The new study was headed by Michael Eriksen Benros, PhD, a senior researcher at the National Centre for Register-based Research at Aarhus University, Denmark.

We know that some of the symptoms that you get with infections are very similar to those you get when you’re depressed, You get tired, lose your energy and your mood is affected. This indicates that some of these symptoms remain after the infection has passed. Michael Eriksen Benros

The study is based on medical data from 3.56 million Danes. Around 90,000 of these have had either a depression or bipolar disorder.

”Unlike anywhere else in the world, in Denmark we have the opportunity to follow the medical history of the entire population by combining hospital records with psychiatric records,” says Benros.

Similar symptoms

Exactly how infections and autoimmune diseases correlate with depression at the molecular level is not entirely clear.

But the researchers have some suggestions about how the two are statistically linked:

The idea for this present study actually came from some animal studies, which showed that animals get depression-like symptoms when they are injected with bacteria that activate their immune system. Michael Eriksen Benros

”We know that some of the symptoms that you get with infections are very similar to those you get when you’re depressed,” says Benros. “You get tired, lose your energy and your mood is affected. This indicates that some of these symptoms remain after the infection has passed.”

Many possible explanations

Previous research has also shown that many people who take medication that stimulates the immune system develop depressive symptoms.

”The idea for this present study actually came from some animal studies, which showed that animals get depression-like symptoms when they are injected with bacteria that activate their immune system.”

According to the researcher, mouse trials have also shown that the animals develop depressive and psychosis-like symptoms when they are given specific antibodies that are produced in some autoimmune diseases.

The immune system is the common denominator

One thing that infections and autoimmune diseases have in common is that the immune system is involved in both.

When you are infected with a bacterium, the immune system responds and kills it.

If you have an autoimmune disease, the immune system responds to something inside the body, which is otherwise not dangerous. It is, however, unclear whether the correlation can be attributed to the immune system.

”Another possiblity is that you may be genetically predisposed to both depression and the two diseases,” says Benros.

------------------------

Read the Danish version of this article at videnskab.dk

Translated by: Dann Vinther

Scientific links

Related content