Most people are familiar with probiotics as “good bacteria” that support a healthy digestive tract. One area that’s gaining more awareness is how they also play important roles in supporting our immune health too. From birth, the microbiome, the community of microbes in our digestive tract, starts to develop and it communicates with our immune system, helping it grow and develop as we do. Some of this communication is local, with immune cells and nodes in our intestinal lining, but there’s also indirect communication at a distance through signaling molecules and various substances that get absorbed into our bloodstream and carried elsewhere.
Probiotics support immune health by:
- Helping with maturation of the innate (first response) immune system early in life*
- Discouraging growth of pathogenic bacteria and other “bad” microorganisms*
- Supporting the intestinal lining as a barrier to pathogens and entry point for nutrients*
- Using chemical signaling to support the health and response of immune system*
- Creating short-chain fatty acids by fermenting fiber (more on why this matters below)*
An example of how probiotics influence our immune health outside of the gut can be found in a number of meta-analyses of clinical trials on probiotics for respiratory infections. One meta-analysis1 pooled results of 20 studies that involved both children and adults. Lactobacillus and Bifidobacterium species of probiotics were shown to reduce the duration of illness and severity of symptoms for respiratory infections due to cold and flu. Two other meta-analyses2,3 also came to the same conclusion: that probiotics are more effective than placebo in reducing the effects of respiratory infections.
Action at a Distance
This begs the question: how can little bacteria in the gut exert immune effects in the lungs, which they have no way of reaching?
To answer this, let’s take a closer look at what exactly these little critters are doing for us in the intestines. Probiotics act on both the innate (what we’re born with) and acquired immune systems and have the potency to decrease the severity of infections in the gastrointestinal and upper respiratory tracts.* So, they act both locally and at a distance by communicating with our immune system.
Probiotics have been found to4:
- Modulate the “cross-talk” between our native bacteria and the mucosal immune system (sort of an ongoing, dynamic dialogue to keep our gut immune system in balance)
- Stimulate type 1 interferon production (this has anti-viral properties)
- Help maturation and regulation of dendritic cells, which aid homeostasis and appropriate immune response systemically.*
Dendritic cells are like messengers between the innate and adaptive aspects of our immune system. They help prime the response of adaptive immune cells to specific antigens (found on pathogens) and teach tolerance towards non-pathogenic molecules/microbes. They help balance our immune response and probiotics support their health and growth.
- Create short-chain fatty acids (SCFA) from fiber. SCFAs like butyrate modulate our immune response, downregulating excess inflammation.*
- Help to increase lymphocytes of the adaptive immune system (probiotics like B. infantis for example)*
- Increase Natural Killer cells and antigen specific B cells (Natural Killer cells sound like ones you don’t want to mess with if you’re a microbe – they’re especially good at taking out virally-infected cells)*
- Help to clear infections quickly while repairing and reducing inflammatory damage*
Many of these effects have system-wide reverberations. Messages and molecules from the gut spread systemically to support immune health in a wider circle – like with the response to respiratory infections we looked at earlier.
Immune System Equilibrium
Our immune system is all about balance. Knowing when to react strongly to infectious microbes and when to ignore something (like pollen). Sometimes this doesn’t work as well as we’d like. People get auto-immune diseases where the immune system attacks our own cells and tissue. Sometimes cancer cells or microbes evade our immune system and don’t trip any alarms until they’ve multiplied and taken root. Research is showing more and more that probiotics, from birth, play a key role in how our immune system grows and develops and responds to the challenges of life.
1. King, S., Glanville, J., Sanders, M., Fitzgerald, A., & Varley, D. (2014). Effectiveness of probiotics on the duration of illness in healthy children and adults who develop common acute respiratory infectious conditions: A systematic review and meta-analysis. British Journal of Nutrition, 112(1), 41-54.
2. Wang Y, et al. Probiotics for prevention and treatment of respiratory tract infections in children: A systematic review and meta-analysis of randomized controlled trials. Medicine (Baltimore). 2016 Aug;95(31):e4509.
3. Hao Q, Dong BR, Wu T. Probiotics for preventing acute upper respiratory tract infections. Cochrane Database Syst Rev. 2015 Feb 3;(2):CD006895.
4. Kanauchi O, Andoh A, AbuBakar S, Yamamoto N. Probiotics and Paraprobiotics in Viral Infection: Clinical Application and Effects on the Innate and Acquired Immune Systems. Curr Pharm Des. 2018;24(6):710-717.
5. Frei R, Akdis M, O’Mahony L. Prebiotics, probiotics, synbiotics, and the immune system: experimental data and clinical evidence. Curr Opin Gastroenterol. 2015 Mar;31(2):153-8.