Although clinical research on how the body fights viral infections is not a new field of interest, the current global pandemic has brought a broader audience and a renewed sense of interest in the latest scientific evidence. While probiotic supplements should certainly not be considered a treatment or cure for viral infection, it appears there may be some connection between a well-balanced population of gut bacteria and a strong immune system that is well supported to fight viral invasion.

Science has shown that species and populations of gut bifidobacteria (strains of which are used in probiotic supplements) naturally decrease with age, and this factor may be linked to the gradual decline of the immune system and associated higher risk of infection [1]. We do have some ability to manipulate our immune systems through diet and lifestyle choices however, and balancing the gut may be a great place to start.

What are probiotics?

Probiotics are living microorganisms (bacteria and yeasts) that are beneficial to the digestive system when consumed through foods or supplements. The name is quite literal, as these organisms are “pro”, in that they support and promote “biotics”, a Latin-derived word for living things. The fundamental difference separating a probiotic from harmful bacteria is their symbiotic, or mutually beneficial, relationship with your body. The human gastrointestinal tract contains trillions of gut bacteria and yeast cells, collectively known as “gut flora” or the gastrointestinal microbiome, made up of more than 500 different bacterial species. This is the largest accumulation of bacteria in any organ system. Beneficial bacteria in the digestive tract have the ability to interact and communicate with immune cells, intestinal cells, and neurons in the body to influence digestive health, immune health, and overall well-being. For the gastrointestinal system to function properly, gut flora must be in balance. 

Taking a daily probiotic supplement or eating probiotic foods can help to make sure your gut is constantly acquiring new, beneficial species of microbes as toxic, harmful bacteria are flushed from the digestive tract. Over time, the established populations of good bacteria will take root, multiply independently, and the effects of this change can be measured throughout the body.

How do probiotics help the body fight a virus?

When a virus enters the body, its DNA is programmed to invade the host’s cells. In some cases, such as with coronavirus, there is a particular cell type that the virus targets, as it binds a certain protein made by those cells. Coronavirus, for instance, binds an enzyme made by cells in the lungs and small intestine. Once viruses have invaded, they kill the host cells, inducing inflammation, and paving the way for bacterial infection and potential failure of the invaded organ. A race ensues between the virus’ ability to kill host cells and the host’s ability to stop the damage. 

Probiotics can help by supporting the body’s natural ability to shut down viral damage by enhancing innate immunity, regulating adaptive immune responses, and modulating pathogen-induced inflammation [2]. When the gut is lined with beneficial, probiotic bacteria, the growth of toxins and potentially harmful bacteria is limited, as there is only so much surface area for adherence inside the intestinal walls. In addition, probiotics have been associated with the increased production of protective antibodies, alongside the boosted production of immune cells such as natural killer cells, and the modulated function of dendritic cells, macrophages, and T and B lymphocytes [2-4]. Natural killer cells are the first to respond to viral invasion, while the other immune cells are involved in the long-term fight or “adaptive immune response” to an invader. 

Probiotics have also been linked with reduced inflammatory cytokine production in response to both viral infection and allergens, showing a possible anti-inflammatory effect [2]. 

Should I wait until I’m sick to take probiotics?

Two meta-analyses recently published by the York Health Economics Consortium (YHEC) and Cochrane reported that probiotic supplementation reduced the incidence and duration of respiratory tract infections (ranging from mild colds to flu-like symptoms), the number of antibiotic courses patients were prescribed, and the days that patients were absent from work [5]. In these studies, participants were assigned to a daily regimen of taking a probiotic supplement or a placebo over the course of a year, so the effects should be recognized as strengthened immune defense, not as a treatment for an established disease.

Respiratory tract infections as a result of viral infection are not a new phenomenon, nor are they associated with only one type of virus. And in fact, quite a bit of research has been dedicated to the connection between gut health and respiratory health over the years. Again, probiotics should not be considered a treatment for any disease, but they can support your body’s natural preventative systems against disease and may be especially supportive in the case of respiratory infection of viral origin. Probiotics are safe to take if you are fighting an infection, but balancing your gut microbiome is typically a gradual process. Research suggests that an established probiotic regimen is probably more effective in supporting the processes that protect your body from the onset of symptoms. Give your body a head start by taking a daily probiotic supplement while you are feeling healthy and strong to support your natural defenses should you become exposed to a virus.


  1. Kato, Kumiko, et al. “Age-related changes in the composition of gut Bifidobacterium species.” Current microbiology 74.8 (2017): 987-995.
  2. Yan, Fang, and D. B. Polk. “Probiotics and immune health.” Current opinion in gastroenterology 27.6 (2011): 496.
  3. Reid, Gregor, et al. “Potential uses of probiotics in clinical practice.” Clinical microbiology reviews 16.4 (2003): 658-672.
  4. Ouwehand, Arthur C., Seppo Salminen, and Erika Isolauri. “Probiotics: an overview of beneficial effects.” Lactic acid bacteria: genetics, metabolism and applications. Springer, Dordrecht, 2002. 279-289.
  5. Lenoir-Wijnkoop, Irene, et al. “Probiotics reduce healthcare cost and societal impact of flu-like respiratory tract infections in the USA: An economic modeling study.” Frontiers in pharmacology 10 (2019): 980.