From NPR. The article is titled “Could Depression Be Caused By An Infection?” I think this title is really incomplete, because they implicate bacteria, viruses, and protazoa, and the relationships between each of these and inflammation and autoimmune disease. The quotes below also suggest that the gut biome, as part of the immune system, must necessarily also be involved.

“The truth of the matter is that there is probably a subset of people who get depressed in response to inflammation,” says lead author Dr. Charles Raison, a psychiatry professor at the University of Arizona. “Maybe their bodies generate more inflammation, or maybe they’re more sensitive to it.”

How infection and other causes of inflammation and overly aggressive immune activity may contribute to depression and other mental illnesses — and whether or not it’s actually depression driving the inflammation — is still being investigated, and likely will be for some time. But plenty of leading psychiatrists agree that the search for alternative pathologic explanations and treatments for psychiatric disorders could help jump-start the field.

“I’m not convinced that anti-inflammatory strategies are going to turn out to be the most powerful treatments around,” cautions Raison. “But I think if we really want to understand depression, we definitely have to understand how the immune system talks to the brain. I just don’t think we’ve identified immune-based or anti-inflammatory treatments yet that are going to have big effects in depression.”

But the University of Toronto’s McIntyre has a slightly brighter outlook. “Is depression due to infection, or is it due to something else?” he asks. “The answer is yes and yes. The bottom line is inflammation appears to contribute to depression, and we have interventions to address this.”

McIntyre notes that while the science of psychiatry has a long way to go, and that these interventions haven’t been proved effective, numerous approaches with minimal side effects exist that appear to be generally anti-inflammatory, including exercise, meditation and healthy sleep habits.

Clearly, trying to maintain the gut biome that is best for each individual will go a long way toward not just physical health, but also mental health.