A new Danish study has found that people who have been hospitalized for a serious infection are at a higher risk for suicide. Researchers think that perhaps it has to do with the inflammation in the brain as a result of the infection, though there a few possibilities.
The study examined the Danish national registry, combing through records of 7.2 million people from 1980 to 2011. Using this information, it was found that those who had been hospitalized for infections had a 42% increased risk for death by suicide compared to those who were hospitalized for other reasons. 
However, this study doesn’t demonstrate a cause and effect, but researchers already know that inflammation can cause depressive symptoms. The researchers even found that 1 in 10 suicides might be linked to infections.
The results, which were published in JAMA Psychiatry, might give weight to the theory that depression is a disease rooted in inflammation. This theory has been proposed by several smaller studies, and this larger study strengthens the theory.
In fact, a 2015 study published in the Annals of Gastroenterology found that of those who were given medication that prompted brain inflammation, one third to one half of them developed symptoms of major depression. 
However, it is important to note that the majority of people who have died by suicide do not have a history of inflammatory infections. Likewise, most people with inflammatory infections do not die by suicide.
“The numbers indicating an increased risk for suicide after severe infections are high, perhaps surprisingly high even for us working with this subject,” said Lena Brundin neurobiologist at the Van Andel Research Institute and Michigan State University who was not involved in the study.
Researchers note that the longer someone had an infection, the higher their risk was for suicide, possibly confirming that the longer the inflammation continues, the more depressive symptoms manifest.
“Provided that the association between infection and the risk of death by suicide was causal, identification and early treatment of infections could be explored as a public health measure for prevention of suicide. Still, further efforts are needed to clarify the exact mechanisms by which infection influences human behavior and risk of suicide,” researchers wrote of the study.
An editorial connected with the study concluded with:
“The findings in the article by Lund-Sørensen suggest that 10.1% of suicides could be attributable to the effects of a severe infection. It will be important to understand how milder and long-term infections contribute to depression and suicidality … Future research is warranted in this area and might indicate that individuals with depressive and suicidal behavior can benefit from the detection and eradication of such pathogens.”
 Live Science
Anna Scanlon is an author of YA and historical fiction and a PhD student at the University of Leicester where she is finishing her degree in modern history.