People with depression or bipolar disorder have an imbalanced gut microbiota

Breaking new ground 9. sep 2021 4 min Professor Maj Vinberg, Postdoctoral fellow and doctor Klara Coello Written by Kristian Sjøgren

Increasing evidence suggests that the composition of gut microbiota is associated with the risk of developing an affective disorder such as bipolar disorder or depression. A study in Denmark investigated potential beneficial and harmful bacteria of the gut in patients with affective disorders.

Can people eat their way to mental health or depression?

Indications are increasing that affective disorders such as bipolar disorder and depression are associated with the composition of our gut microbiota.

Our upbringing, environment, genes and eating habits all influence our gut bacteria. A new study in Denmark examined the composition of gut bacteria among people with affective disorders and reveals that these people have relatively few beneficial bacteria and presence of harmful bacteria  compared with healthy individuals.

“The study emphasises the complex association between the composition of our gut microbiota and affective disorders, and our findings suggest that deviation from a healthy microbiome increases the risk of developing affective disorders. In the future, if we can better understand this association, we can explore new treatment methods and hopefully help people with these potentially incapacitating disorders earlier and more effectively,” explains a researcher behind the study, Maj Vinberg, Clinical Professor, Department of Clinical Medicine, University of Copenhagen and Mental Health Services Centre Nordsjælland.

Maj Vinberg collaborated on the study with Klara Coello, a postdoctoral fellow and doctor based at Mental Health Services Centre Copenhagen.

The research has been published in Progress in Neuropsychopharmacology and Biological Psychiatry.

Previous studies associated affective disorders and gut bacteria

Maj Vinberg has led several studies that have investigated the association between affective disorders and an imbalanced composition of gut microbiota.

She investigated the presence of beneficial and harmful bacteria in the intestines of twins, one of whom had either depression or bipolar disorder and the other did not.

This research was the subject of a previous article.

In another study, Klara Coello and Maj Vinberg found that people newly diagnosed with bipolar disorder more often had Flavonifractor bacteria in their gut compared with healthy controls. Flavonifractor bacteria can reduce the body’s stores of quercetin, which has both anti-inflammatory and antioxidant properties.

In the new study, the researchers collected data from the two previous studies to investigate further whether the quantities of specific types of bacteria in the intestines are associated with mental health.

“There are very few studies of the composition of gut microbiota among people with affective disorders, and we therefore decided to carry out this larger study to determine whether we could replicate our previous findings,” says Maj Vinberg.

Examined the gut bacteria of 347 people

The researchers determined the abundance and prevalence, respectively, of two types of bacteria among 347 people.

· The Christensenellaceae family of bacteria is positively associated with health and regulates the accumulation of fat in the body.

· The Flavonifractor genus is negatively associated with health by promoting inflammation and enhanced oxidative stress.

Of the 347 trial participants, 176 had either bipolar disorder or depression, 70 were parents, siblings or children of people with affective disorders and 101 were healthy controls.

Stool samples were examined for the abundance of Christensenellaceae and the prevalence of Flavonifractor.

Major differences in the composition of gut bacteria

The patients with bipolar disorder or depression more often had Flavonifractor in their gut bacteria than healthy controls.

Conversely, the healthy controls had higher counts of the healthy Christensenellaceae in their gut.

“The combination of more Flavonifractor and less Christensenellaceae is also consistent with the fact that people with affective disorders are twice as likely as the general population to develop type 2 diabetes and cardiovascular disease – and at a significantly younger age than the general population.” Explains Klara 

The researchers also examined oxidative stress, which is associated with poor health. People with Flavonifractor in their gut microbiota generally had higher oxidative stress in the body.

Maj Vinberg explains that the direction of causation is still an open question – whether an unhealthy composition of gut bacteria leads to an increased risk of developing affective disorders or whether affective disorders can influence the bacteria in the gut.

However, in the twin study, the researchers found that the presence of Christensenellaceae in the participants’ gut microbiota had a hereditary component. This indicates that an unhealthy composition of gut bacteria may emerge before affective disorders develop. The healthy close relatives slightly more often had Flavonifractor and had slightly fewer Christensenellaceae, but these differences were not statistically significant.

“Genetic factors are one of the big questions researchers are exploring across many diseases. But this is so complex that we do not have an answer yet,” explains Maj Vinberg.

Smoking can push the gut microbiome over the edge

The study also indicates that smoking may influence the risk of having unhealthy gut bacteria, having fewer Christensenellaceae and more often having Flavonifractor in the gut microbiota.

This indicates that smoking may not inherently trigger affective disorders but may be the straw that breaks the camel’s back.

“Although people may already have several predisposing factors for developing affective disorders, whether they smoke or not seems to matter. Being predisposed and an active smoker may contribute to adversely affecting the microbiota that is already not functioning optimally, and this may create interaction between genes and the environment that promotes affective disorders,” says Maj Vinberg.

Can we eat our way to health or disease?

Conversely, the gut microbiome may also protect people from developing affective disorders.

According to Maj Vinberg, having a healthy and strong microbiome could protect people from developing affective disorders.

These individuals may be able to tolerate many factors that might otherwise predispose them to developing affective disorders.

“There is considerable focus on how to achieve a health-promoting composition of gut bacteria. You can promote a healthy composition by eating a varied diet including lots of vegetables and prebiotic fibre, but we do not yet know to what extent this prevents or mitigates disease. Several trials are underway on transplantation of the gut microbiome between humans, and animal trials for treating anxiety and depressive disorders are promising. In addition, research is being carried out into whether probiotic supplements can make a difference. Although we know that the gut and the brain communicate through chemicals, hormones, the immune system and nerves, this is a complex field. Elevated stress hormone can also affect the gut microbiota negatively, and we can therefore also imagine that improving sleep and activating the parasympathetic nervous system can benefit gut microbiota and promote health. These are the long-term perspectives, but we still lack data for understanding the relationship between the composition of gut bacteria and affective disorders and using this in clinical practice,” explains Klara Coello.

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