Can Probiotics Prevent Colds and Flu?

As the weather cools down, colds, coughs and respiratory infections tend to become more common. Many people start looking for ways to support their immune system through winter, and probiotics are often suggested as one possible option.

Probiotics are best known for supporting digestive health, but the gut also has an important relationship with the immune system. This has led researchers to explore whether certain probiotic strains may help reduce the likelihood, frequency or duration of some respiratory infections — though probiotics are not all the same, and their effects can depend on the specific strain, dose, length of use and the individual taking them.

So, should you take probiotics during cold and flu season? In this article, we'll look at how gut health and immunity are connected, what the research actually says, and how to choose a probiotic worth trying this winter.

What are probiotics?

Probiotics are live microorganisms, including certain types of bacteria and yeasts, that may provide a health benefit when consumed in adequate amounts. They are often called “good” or “beneficial” bacteria because they can help support the natural balance of microorganisms in the gut.

Probiotics are available in several forms, including:

• Capsules and powders

• Probiotic yoghurt containing live cultures

• Fermented milk drinks

• Some fermented foods

Each format delivers live microorganisms in a slightly different way, and the strains included can vary widely from one product to the next. 

Probiotics are different from prebiotics. Probiotics are the live microorganisms themselves, while prebiotics are certain types of fibre that feed beneficial bacteria already living in the gut. Foods such as oats, legumes, onions, garlic and some fruits and vegetables contain prebiotic fibre.

What does your gut have to do with immunity?

It might seem strange that something happening in your digestive tract could have anything to do with catching a cold, but the connection is more direct than most people realise. Your digestive tract is home to trillions of microorganisms — collectively known as the gut microbiome — and this community does far more than just help digest food. It also plays a significant role in how your immune system functions.

The gut lining acts as a protective barrier

The lining of your gut isn't just a passageway for digestion; it's one of the body's largest barriers against harmful organisms and substances. A healthy gut lining, supported by a balanced microbiome, helps keep unwanted bacteria, toxins and pathogens from passing into the bloodstream, while still allowing nutrients through.

Gut microbes and immune cells are in constant communication 

A large proportion of the body's immune cells are actually located in and around the gut. Beneficial gut bacteria interact with these immune cells, helping to train and regulate how the immune system responds to threats. This communication can influence how effectively your body recognises and reacts to harmful organisms, including viruses responsible for colds and flu.

Several everyday factors can influence the microbiome

The balance of bacteria in your gut isn't fixed — it shifts in response to diet, illness, medication (particularly antibiotics), stress and ageing. A diet low in fibre and high in processed foods, a course of antibiotics, chronic stress or simply getting older can all reduce the diversity of beneficial bacteria in the gut, which may in turn affect how well the immune system is supported.

Read related article: What Does Your Gut Have to Do With How Fast You Age?

"Supporting immunity" doesn't mean becoming immune to infection

 This is an important distinction. A well-balanced gut microbiome may help the immune system function more effectively, but this isn't the same as being protected from getting sick. No probiotic, supplement or food can guarantee you won't catch a cold or the flu this winter. At best, a healthy gut may contribute to a more responsive immune system — one possible factor among many, rather than a shield against infection.

Can probiotics prevent colds and flu?

There is some evidence that certain probiotics may help reduce the risk or duration of acute upper respiratory tract infections. However, this does not mean that probiotics can guarantee protection against colds or influenza.

A 2022 Cochrane review, Probiotics for Preventing Acute Upper Respiratory Tract Infections, examined research comparing probiotics with a placebo or no treatment. It found that probiotics may reduce the number of people who experience at least one acute upper respiratory tract infection and may slightly shorten how long an infection lasts. However, the certainty of the evidence varied, the studies tested different probiotic strains and doses, and the researchers noted that more studies involving older adults were needed.

Upper respiratory tract infections affect areas such as the nose, sinuses and throat and include illnesses such as the common cold. Influenza, commonly called the flu, is a specific viral infection caused by influenza viruses. Evidence suggesting that probiotics may help with upper respiratory tract infections does not prove that they can prevent influenza specifically.

Probiotic benefits depend on the strain

The strain code is important because research involving one strain cannot automatically be used to support claims about another strain—even when both belong to the same species. Similarly, a study on one individual strain does not prove that every general or multi-strain probiotic will provide the same result.

Some commonly studied probiotics include:

• Lactobacillus rhamnosus GG – studied for digestive health and reducing the risk of some types of antibiotic-associated diarrhoea

• Saccharomyces boulardii – a beneficial yeast studied for antibiotic-associated and some forms of infectious diarrhoea

• Bifidobacterium animalis subsp. lactis – studied for digestive regularity, gut health and aspects of normal immune function

• Lactobacillus acidophilus – commonly included in digestive health products and studied for lactose digestion and gut balance

• Limosilactobacillus reuteri – studied for several digestive and oral health applications, with benefits depending on the specific strain

• Bifidobacterium longum – studied for digestive comfort and its interaction with the gut microbiome

These are broad examples only. The evidence may differ between individual strains, doses, product combinations and health concerns.

When reading a probiotic label, look for:

• The full genus, species and strain name

• The number of colony-forming units, shown as CFU

• Whether the CFU count is guaranteed through the expiry date

• The recommended dose

• Storage instructions, such as whether refrigeration is required

• The expiry date

A higher CFU number or a longer list of strains does not necessarily make one probiotic better than another. It is more useful to look for a clearly identified strain that has been researched for the reason you are considering taking it.

Read related article: Choosing the Right Probiotic: The Benefits of Different Strains for Your Health

Should you start taking probiotics once you feel sick?

Starting a probiotic after cold or flu symptoms appear is unlikely to provide an instant remedy. Much of the research into probiotics and respiratory infections has looked at people taking them regularly over time as a preventive measure, rather than beginning treatment once they are already unwell. 

If you already take a probiotic for digestive health or another reason, you may choose to continue following the product directions. However, starting one when symptoms appear should not replace rest, fluids, appropriate medicines or advice from a health professional.

Seek medical advice if your symptoms are not improving or are becoming worse. Do not delay care if you experience warning signs such as:

• Difficulty breathing or shortness of breath

• A persistent or very high fever

• Signs of dehydration

• Chest pain

• Confusion or unusual drowsiness

• Symptoms that continue to worsen

Probiotics are only one part of winter wellness

Probiotics may have a place in a winter health routine, but they should not be treated as the main line of defence against colds, influenza or other respiratory infections.

Supporting your health during winter, reducing your risk of infection and managing symptoms when you become unwell involves several everyday habits working together. These include:

• Staying up to date with recommended vaccinations

• Washing your hands regularly or using hand sanitiser when soap and water are not available

• Wearing a well-fitting mask in crowded indoor spaces, healthcare settings or when caring for someone who is unwell

• Covering coughs and sneezes

• Staying home when you are unwell

• Getting enough sleep

• Eating a varied and balanced diet

• Staying physically active

• Drinking enough water

• Testing or seeking medical advice when appropriate

Because colds, influenza and COVID-19 can cause similar symptoms, it may not always be easy to tell what is making you unwell based on symptoms alone. 

At-home rapid antigen tests can help narrow this down. These tests are typically designed to detect specific viruses such as influenza A, influenza B and COVID-19, with some combination tests also covering RSV and adenovirus. 

It's worth noting that they generally aren't testing for "the common cold" itself, since colds can be caused by a wide range of different viruses that aren't usually included in these panels. Still, testing for the more specific viruses can be useful, as a positive result tells you which virus is responsible, while a negative result across these tests makes a common cold a more likely explanation for your symptoms.

A negative result doesn't completely rule out infection, so it's important to follow the test instructions and seek medical advice if symptoms are severe, worsening or persistent.

👉 Shop at-home rapid antigen and combination tests online at Aussie Pharma Direct.

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