Nobody likes getting sick, and cold and flu season can feel like an obstacle course. Probiotics are best known for digestion, but your gut bacteria also play a big part in how your immune system works. Here is how that connection works, what the research says about probiotics and colds, and which strains have been studied most.
Why do gut bacteria matter for immunity?
Your body is home to trillions of microorganisms, mostly bacteria, along with yeasts and viruses, living on your skin, in your mouth and above all in your gut. You may have read that we are "only 10% human." That old figure has been revised: a 2016 analysis estimated about 38 trillion bacteria in the body, roughly the same number as human cells, with a total mass of about 0.2 kg.
These microbes do real work. Some bacteria help digest food, destroy disease-causing cells or produce vitamins. And because the gut is where your body meets the outside world every day, through everything you eat and drink, it is also a major immune hub.
How is the gut connected to the immune system?
The gut-associated lymphoid tissue represents almost 70% of the entire immune system, and about 80% of antibody-producing plasma cells reside there. Its job is to let nutrients in and keep harmful material out, and to tell the difference between a threat and a meal.
Your gut bacteria help with that job. Probiotics are thought to work by interacting with immune cells in the gut lining and influencing inflammatory gene expression, by competing with less friendly microbes for space and food, and by helping maintain the gut barrier. When the community is balanced, it supports normal immune function. When it is disrupted, by antibiotics, a poor diet or chronic stress, that support can weaken. Our article on chronic stress and gut health explains how stress plays in.
Can probiotics help you get fewer colds?
The best summary of the evidence is a 2022 Cochrane review of 23 trials and nearly 7,000 children, adults and older people. It found that probiotics may reduce the number of people who get at least one upper respiratory infection by about a quarter, may shorten episodes by about a day, and likely reduce antibiotic use for these infections. The certainty of the evidence was low to moderate, and most studies used one or two specific strains for three months or more.
That is a meaningful but modest effect. Probiotics are a support for your immune system, not a guarantee against catching a cold.
Which probiotic strains have been studied for immunity?
Effects are strain-specific: if one kind of Lactobacillus helps, another kind will not necessarily do the same. A few strains have been studied more than most:
Lactobacillus rhamnosus GG (LGG)
In a randomized trial of 742 hospitalized children, those given LGG in a fermented milk drink had a significantly lower risk of gastrointestinal and respiratory tract infections than children given a placebo drink.
Lactobacillus paracasei
Strains of L. paracasei are among the strains most often used in the trials included in the Cochrane review of probiotics for upper respiratory infections.
Lactobacillus acidophilus NCFM
In a study of 326 children aged 3 to 5, six months of L. acidophilus NCFM twice daily reduced fever incidence by 53% and coughing by 41% compared with placebo, and combining it with Bifidobacterium lactis Bi-07 had even larger effects.
How to support your immune system year-round
Probiotics work best on top of the basics: enough sleep, a varied diet rich in plants and fiber, regular movement, and stress management. Fermented foods count too; see 3 Keys to a Healthy Microbiome.
If you want a daily probiotic, Trust Your Gut Probiotic + Prebiotic Daily Essential contains 16 billion CFU from 6 strains researched for their potential to support digestion and the immune system, plus organic prebiotics. For something you do not have to swallow, Pre + Probiotic Pixies melt in your mouth, and Pre + Probiotic Pixies for Kids are made for ages 4 and up. Read more about the biggest benefits of probiotics.
If you are immunocompromised, seriously ill or pregnant, or considering a probiotic for a young child with health conditions, talk to your doctor first.
