The Surprising Link between Infections And Suicide
According to a study published online on August 10 in JAMA Psychiatry, getting an infection that requires hospitalization has been linked to a 42% increased risk of dying by suicide. This finding raises questions about the mechanisms involved and the links between getting an infection that requires hospitalization and having an increased risk of suicide. Some possible explanations point to biological mechanisms such as neuroinflammation and immune alterations and how they may have an effect on suicidal behavior. Another possibility is that suicidal behaviour is a side effect of treatment for the infection, perhaps arising from changes to gut flora caused by antibiotics.
While psychiatric disorders and previous suicide attempts are stronger predictors of suicide, hospitalization with infection accounted for a population-attributable risk of 10.1%. That means that 1 in 10 suicides could be prevented if infections were eliminated entirely.
Putting the Focus on Biology not Psychology
Many researchers have studied psychological and behavioral predictors of suicide however few have studied biological factors, such as infection. After controlling for many factors such as age, sex, and socioeconomic status, researchers found that the risk of suicidal behaviour increased in a “dose-dependent” manner with the highest incidence of suicide among those with more hospitalizations due to infections. The amount of time spent in the hospital for infection treatment was also associated with an increased suicide risk.
The highest risk of suicide was among patients with hepatitis. This is consistent with previous studies that have shown that patients with hepatitis present a higher suicidal ideation and behavior that the general population. Hepatitis is an inflammatory disorder caused by a virus.
Bacterial infections were only associated with a slightly higher risk for suicide compared to viral infections, an association that was not significantly significant. This suggests that the cause may be linked to the immune response itself rather than a side effect of antibiotic treatment. Still, given the effects of antibiotic treatment on the microbiome, those microorganisms that share our body, it can’t be ruled out completely.
There are many potential mechanism linking infections to suicidal behavior. Some infections infect the brain directly however most affect other parts of the body and may affect the brain indirectly. For example, influenza B virus and the parasite Toxoplasma gondii have both been linked to suicidal behavior. The latter has also been shown to be associated with impulsivity and aggression in psychiatric patients and healthy adults alike.
Most would have expected that a history of psychiatric issues would explain away the correlation. Surprisingly, this study found that even when controlling for a history of psychiatric issues, there was still a 30% increase in risk of suicide, even among those with no history of any psychiatric illnesses.
People who have recently attempted suicide have been shown to have increased levels of inflammation. It was perhaps thought that this was a consequence of the suicide attempt and not necessarily a condition that preceded it. Researchers speculate that an infection may alter the immune system in such a way that may play a role in suicidal behaviour. Evidence points to an inflammation-induced depression. An editorial by Brundin and Grit, noted that infections trigger inflammation and thus may activate inflammatory mechanisms leading to depression and suicidal symptoms.
While we can’t know for sure that there is a causal link between infection and suicide, we do know that inflammation is present in patients with depression and, in particular, in patients with suicidal ideation and behavior. We know that inflammation affects the brain and can cause depressive symptoms. What we don’t know is where this inflammation originates from.
One of the most troubling conclusions about a possible link between infection and suicidality is that infections can be of low grade and long term and still be associated with an increased risk of suicide.
This research should help pave the way for novel treatment studies to determine the effects of different therapies on depression and suicidality. For example, the treatment of chronic infections with antibiotics along with anti-inflammatories could be considered in psychiatric patients already at an increased risk of suicide.
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