How probiotics help the immune system

There's mounting evidence that improving your gut health with probiotics (and prebiotics and postbiotics) can boost your body's immune health and reduce the impact of viral infections such as colds and 'flu.

🕒 5 min read

If you're looking to improve your immune system before heading into peak cold and 'flu season, you could start by trying to improve the health of your gut. Or more specifically, the trillions of microorganisms that make up the gut microbiome (which includes bacteria but also fungi, parasites and viruses.)

When we're healthy these bugs live peacefully side by side in the small and large intestines, and help to perform crucial roles in the body, including digesting food, synthesising vitamins such B and K and bolstering immunity. The gut connects to the immune system through a series of pathways known as the gut-immune axis.

A healthy gut microbiome containing a delicate balance of the diverse beneficial bacteria that live in the gastrointestinal tract is vital for healthy immunity, and this relationship is a bidirectional one. In short, the health of your immune system can affect your gut, and the state of your gut microbiome can have a direct effect on your immune system.

This is perhaps unsurprising when we consider that the body's digestive system contains over 70% of the body's immune cells, so if you are prone to getting frequent colds, coughs, flus or stomach bugs, it could be that your gut bugs are out of balance and need some attention.

The gut-immune axis

The precise mechanisms by which the gut influences the immune system are not yet fully understood, but we do know that immune cells in the gut interact with the microbiome and are directly influenced by our diet and lifestyle.

The foods we eat affect the diversity and composition of bacteria, and the key is to eat a varied and healthy diet, as dietary diversity is known to lead to microbial diversity.

If there is a disturbance in the balance of the microbiota, due to illness, poor diet, lack of sleep, dehydration, chronic stress or prolonged use of medications, particularly antibiotics, you would be at greater risk of a weakened immune system and therefore disease.

Studies show that good-quality sleep is linked to a greater diversity of species of gut microbiota, and too much ultra-processed food can also have an impact.

Dysbiosis

If the balance of gut bugs becomes imbalanced, creating a condition known as dysbiosis, this can contribute to inflammation in the body and potentially, over time, leading to the development of conditions such as Inflammatory Bowel Disease (IBD), asthma and autoimmune conditions including rheumatoid arthritis or lupus.

Put simply, this inflammatory response does little to support your overall health or immunity and is going to make it harder for your body to fight disease, infection and viruses.

Diet and the microbiome

Diet is one of the main modulators of the gut microbiota, and eating a well-balanced diet rich in plenty of fruit and vegetables, healthy fibre and lean protein can help to balance the bacteria in your gut.

Probiotic and prebiotic foods and supplements have also been shown to have a beneficial effect on your gut microbiome.

What exactly are probiotics?

Probiotics are live microorganisms that appear to have health benefits when eaten, and have been shown to modify and restore the balance of bacteria in the gut.

Found in fermented foods such as live unsweetened yogurt, aged cheeses, sourdough bread, kefir (a fermented milk drink), miso (fermented soybeans), pickled vegetables like gherkins and other fermented foods like sauerkraut and kimchi, these are 'good' bugs that add to the diversity of bacteria in your intestinal tract.

They can also be found in supplement form. Generally, the higher the strain count of bacteria in your chosen supplement the better for creating a colony of good gut bugs.

Find out more about probiotics.

What about prebiotics and postbiotics?

Prebiotic foods, such as onions, garlic, leeks, asparagus, Jerusalem artichokes, mushrooms, chicory root, cabbage and apples, can make probiotics even more effective.

The prebiotic fibres found in many of these foods act as a kind of fertiliser for the probiotics, helping to 'feed' and strengthen the probiotic bacteria. You can also find prebiotics in supplement form, including those containing inulin: a natural fibre found in chicory root.

Research is also focusing on the role of postbiotics, which are left behind after your body has digested probiotic bacteria and prebiotic bacteria in the gut, and how they can help maintain a healthy immune system. A study on older adults has found that postbiotics may also help strengthen immunity and protect against infections like the common cold. Find out more about postbiotics.

The effects of probiotics on cold and 'flu

Several studies show probiotic supplements, especially those containing Lactobacillus and Bifidobacterium, appearing to improve the body's immune response, helping it to be better prepared to fight off infections such as the common cold.

A Cochrane Review found that probiotics performed better than a placebo in reducing Upper Respiratory Tract Infections (URTIs), and also reduced the duration of an episode by nearly two days if participants did fall ill.

Anecdotally, increasing numbers of health professionals are reporting that since taking probiotic supplements regularly they have had no, or fewer, viral infections. The research seems to support this, with evidence showing that people who regularly take probiotics are sicker for fewer days if they do end up ill.

There is also research to suggest that taking probiotics in combination with prebiotics before getting your annual 'flu jab could increase its effectiveness. Evidence also shows how gut microbes help the lungs to control respiratory viral infections – with prebiotics and probiotics suggested as possible preventative approaches and treatment strategies.

What to look for in a probiotic supplement

When choosing a probiotic, the general advice is to choose one with as many live bacterial strains as possible, particularly the most researched varieties such as Lactobacillus, Bifidobacterium and Bacillus. You should look for a supplement with at least one billion (but ideally up to 50 billion) colony-forming units or CFUs – the number of bacteria per dose.

Be aware that heat can kill off the microorganisms in your probiotics, however, so store them in a cool place to extend their shelf life, and don't take them along with a hot drink. Be patient, too – allow up to 30 days to feel the effects of the probiotic.

Shop Healthspan probiotic supplements.