The Gut Microbiome: Your Body's First Line of Defense
Your gut is home to trillions of microorganisms, including bacteria, fungi, and viruses, collectively known as the gut microbiome [1.4.5]. This complex ecosystem plays a vital role in digestion, nutrient absorption, and, crucially, immune function [1.11.3]. A balanced microbiome helps maintain the integrity of the gut lining, preventing harmful pathogens from entering the bloodstream [1.11.3]. When you get sick, whether from a viral infection like the common cold or gastroenteritis, or a bacterial infection requiring antibiotics, this delicate balance can be disrupted [1.6.1]. This disruption, or dysbiosis, can weaken your immune response and prolong symptoms.
Probiotics are live microorganisms that, when administered in adequate amounts, can offer a health benefit [1.6.5]. The core idea behind taking them during an illness is to replenish beneficial bacteria, support the immune system, and help restore gut balance more quickly [1.6.1].
Probiotics for Specific Illnesses: What the Evidence Says
Research into the effectiveness of probiotics during illness shows promising results for certain conditions, although it's important to note that effects are strain-specific [1.8.3].
Respiratory Infections (Common Cold & Flu) Several studies suggest that regular probiotic use can improve the body's immune response and lower the chances of catching a cold [1.3.2]. If you do get sick, probiotics may help reduce the severity and duration of your symptoms [1.3.2, 1.3.3]. One study in children aged 3-5 found that daily supplementation with Lactobacillus acidophilus NCFM, alone or in combination with Bifidobacterium animalis subsp. lactis Bi-07, for six months significantly reduced the incidence and duration of fever, coughing, and rhinorrhea [1.3.1]. It also led to a dramatic reduction in antibiotic prescriptions [1.3.1]. For adults, some research shows that specific probiotic mixtures can shorten cold episodes by nearly two days [1.3.3].
Gastrointestinal Illness (Diarrhea & "Stomach Flu") This is one of the most well-supported areas for probiotic use. Viral gastroenteritis, often called the "stomach flu," can cause significant discomfort. A systematic review found that probiotics can shorten the duration of diarrhea by about a day and may also reduce hospitalization time in patients with viral gastroenteritis [1.4.1]. Strains like Lactobacillus rhamnosus GG (LGG) and the beneficial yeast Saccharomyces boulardii are among the most studied for treating infectious diarrhea [1.4.4, 1.6.2].
Antibiotic-Associated Diarrhea (AAD) Antibiotics are powerful medicines, but they don't distinguish between harmful and beneficial bacteria, often leading to diarrhea [1.6.1]. A comprehensive analysis of 63 trials concluded that taking probiotics alongside antibiotics reduced the risk of developing AAD by 42% [1.6.1]. Research suggests taking the probiotic a few hours apart from the antibiotic to ensure the beneficial microbes survive [1.10.1, 1.10.3]. High-dose probiotics (≥ 5 billion CFUs/day) appear to be more effective [1.6.2]. Saccharomyces boulardii and Lactobacillus rhamnosus are again considered highly appropriate for preventing AAD [1.6.2].
Probiotic Strains and Their Targeted Benefits
Not all probiotics are the same. Choosing the right strain for your specific illness is key to seeing potential benefits [1.8.3].
| Probiotic Strain | Commonly Associated Illness/Condition | Evidence Highlights |
|---|---|---|
| Lactobacillus rhamnosus GG (LGG) | Antibiotic-Associated Diarrhea, Respiratory Infections | One of the most effective strains for preventing AAD and reducing respiratory infections in children [1.8.3, 1.11.4]. |
| Saccharomyces boulardii | Antibiotic-Associated & Infectious Diarrhea | A beneficial yeast shown to reduce diarrhea duration and prevent relapse of C. difficile infections [1.7.4, 1.6.5]. |
| Lactobacillus acidophilus NCFM | Respiratory Infections | Reduced fever, cough, and antibiotic use in children when taken alone or with B. lactis Bi-07 [1.3.1]. |
| Bifidobacterium animalis ssp. lactis | Respiratory Infections, Immune Support | In combination with L. acidophilus, significantly reduced cold and flu-like symptoms [1.3.1]. |
| Lactobacillus plantarum | General Immune Support | May reduce the incidence of common colds and actively secretes antimicrobial substances [1.3.5, 1.11.4]. |
Potential Risks and Important Considerations
While generally considered safe for healthy individuals, probiotics are not without risks [1.5.3]. The primary concern is for people with weakened immune systems (immunocompromised), such as those with certain illnesses, undergoing chemotherapy, or post-organ transplant [1.5.2, 1.5.4]. In these vulnerable populations, there is a rare risk that the probiotics themselves could cause a systemic infection, like sepsis or endocarditis [1.5.2, 1.5.5].
Other potential side effects are typically mild and temporary, such as gas, bloating, or diarrhea, as your gut adjusts to the new microbes [1.2.3].
It is crucial to talk with a healthcare provider before starting any supplement, especially when you are already sick or have an underlying health condition [1.5.3]. Probiotic supplements are not regulated as drugs by the FDA, so quality can vary [1.5.4].
How to Choose and Use a Probiotic Supplement
If you and your doctor decide a probiotic is a good option, consider the following:
- Match the Strain to Your Need: As shown in the table, different strains have different benefits. Research which strains are backed by science for your specific symptoms [1.8.3].
- Check the CFU Count: Colony-Forming Units (CFUs) indicate the number of viable cells. Dosages in studies often range from 5 to 40 billion CFUs per day for preventing AAD [1.6.2].
- Look for Third-Party Verification: Since the FDA doesn't monitor manufacturing, seals from organizations like USP, NSF, or ConsumerLab provide some assurance of quality and that the product contains what the label says [1.8.4].
- Read the Label: Look for the full strain name (e.g., Lactobacillus rhamnosus GG), the CFU count through the expiration date, and storage instructions [1.8.4].
For an authoritative overview of probiotics, the National Institutes of Health Office of Dietary Supplements provides a comprehensive fact sheet for consumers and professionals.
Probiotics: Fact Sheet for Health Professionals - NIH
Conclusion: A Tool, Not a Cure-All
So, should you take probiotics when sick? The evidence suggests that for common illnesses like respiratory infections and various forms of diarrhea, the right probiotic can be a beneficial tool to potentially shorten the duration and severity of your symptoms [1.3.2, 1.4.1]. They are particularly useful for preventing the gastrointestinal side effects of antibiotics [1.6.1]. However, they are not a magic bullet. Their effectiveness is strain-specific, and they carry potential risks for certain populations [1.5.4, 1.8.3]. Always consult with a healthcare professional to determine if taking a probiotic is safe and appropriate for your individual health situation, especially when you are ill.
