On Nutrition

Research on the role of the gut microbiota in human health is a rapidly evolving area of science. Most of our immune cells reside in the wall of our large intestine, and our gut microbiota — the population of an estimated 100 trillion microorganisms that live in our intestines — provide us with certain benefits our bodies don’t have on their own. These include developing and regulating our complex immune system and resistance against infection. Naturally, this raises questions about the role of probiotics in immune system function — and in COVID-19 prevention.

Probiotics are live microorganisms that benefit our health when we ingest enough of them. Probiotics have been shown to have some benefits for gut health, so given the relationship between our gut and our immune system, it seems like a logical assumption that probiotics can support our immune health. In fact, there are no shortage of claims that probiotics do exactly that. But are these claims backed by science? And does supporting immune health translate to protecting us from COVID-19 or other viruses?

While “boosting” immunity was of interest long before the coronavirus pandemic hit, now it’s a Holy Grail, especially with news of new COVID-19 strains and the slow rollout of the vaccines. Here are two major points to know:

  • We do know that the probiotics we ingest through supplements, foods and beverages can support immune system health in general by helping to protect intestinal health and maintain a healthy balance of gut microbes.
  • There is also some specific evidence showing that certain probiotic supplements can reduce the risk of viral upper respiratory infections such as the common cold. This includes not just the odds of becoming infected, but the length and severity of the illness. However, that evidence isn’t very strong, and probiotics have not been studied specifically for COVID-19 prevention or treatment.

That hasn’t stopped some public health experts from pushing for giving probiotics to COVID-19 patients. Other experts have been pointing out that the argument in favor of using probiotics to fight COVID-19 is based on evidence that has nothing to do with COVID-19, specifically. They recommend not using probiotics for COVID-19 until we better understand the virus’s effects on the gut microbiota.

Specifically, the board of the International Scientific Association for Probiotics and Prebiotics (ISAPP) has stated that not all evidence on probiotics and upper respiratory tract infections is high quality — more clinical trials are needed to confirm these findings, and there are a lot of questions still to be answered. The board also stated that these studies may not be relevant for COVID-19, since it’s not just an upper respiratory infection — it’s also a lower respiratory infection and an inflammatory disease. They wrote: “We reiterate, currently no probiotics or prebiotics have been shown to prevent or treat COVID-19.”

When you consider all the research on the effects of probiotics on human health, very little of that research has focused on the human immune system. While it’s clear that gut health plays a major role in immune system function, it’s too soon to recommend probiotics as a go-to fix for enhancing immunity — especially random off-the-shelf probiotic supplements. First, we need studies of specific doses of specific probiotic strains and how they affect the real-world outcomes you care about, such as how likely you are to get sick, and if you get better faster.

Following up on Carrie Dennett’s interview with Lindo Bacon about their new book, “Radical Belonging,” a few weeks ago, Dennett will be interviewing them live on Instagram on Feb. 11 at 11 a.m. Her handle is @CarrieDennett.