Probing probiotics: 3 evidence-based benefits related to their use

The Bottom Line

  • Probiotics are “good” bacteria. Prebiotics are a food source that promotes the growth of probiotics.
  • Among those taking antibiotics, probiotics can prevent diarrhea associated with the harmful Clostridium difficile bacteria.
  • Taking prebiotic or probiotic supplements before getting the flu shot can increase its effectiveness.
  • In people with a healthy immune system, probiotics may help to prevent acute upper respiratory tract infections. 

Probiotics are living microorganisms, specifically bacteria (1;2). They can be consumed via supplements and certain foods like fermented vegetables, fortified goods, and cultured dairy products. We often discuss bacteria in relation to the wide array of diseases or illnesses that they cause. But, did you know that not all bacteria are “bad”? Some, like probiotics, may result in health benefits when given or taken appropriately (1;3-6). Click on the links below to learn more.

1. Prevent diarrhea               

Antibiotics are important and heavily prescribed medications. However, they can alter the gut's balance of “good” and “bad” bacteria. This imbalance provides an opportunity for harmful Clostridium difficile bacteria to cause potentially fatal bowel diseases or diarrhea (7;8). Research shows that taking probiotics alongside prescribed antibiotics can decrease the risk of developing Clostridium difficile-associated diarrhea (3;4). Probiotics may also help in the treatment of other gastrointestinal issues, such as irritable bowel syndrome and chronic constipation (5).

2. Help flu shots stick

Now let us add prebiotics to the mix. Prebiotics promote the growth of beneficial bacteria, like probiotics, by acting as a food source (9). Research shows that people taking prebiotic or probiotic supplements prior to getting their flu shot can experience greater protection against certain flu strains. Healthy older adults who take the supplements over a longer period may reap the greatest benefits from this strategy. More research is needed to support these findings, discuss safety, and confirm the most optimal supplement combinations, dosage, and timing (6).

3. Thwart upper respiratory tract infections 

Globally, upper respiratory tract infections (URTIs)—like the common cold—are a significant source of illness each year (10). Research shows that in people with healthy immune systems, probiotics may be effective at preventing acute URTIs, decreasing the average duration of an acute URTI episode, and reducing the number of people who use prescribed antibiotics for an acute URTI. Here, probiotics were often consumed with milkā€based food, as capsules, or through a powder formulation. More high-quality research is needed to increase our certainty in these findings, especially for older adults (1).

Consult your healthcare team before adopting a strategy that incorporates either probiotic or prebiotic consumption to determine if this is the best strategy for you. Consider optimal formulations, dose, and timing. Note not all supplements are safe for all people. 

Featured Resources

Get the latest content first. Sign up for free weekly email alerts.
Author Details


  1. Zhao Y, Dong BR, Hao Q. Probiotics for preventing acute upper respiratory tract infections. Cochrane Database Syst Rev. 2022; 8:CD006895. doi: 10.1002/14651858.CD006895.pub4.
  2. Reid G, Sanders ME, Gaskins HR, et al. New scientific paradigms for probiotics and prebiotics. J Clin Gastroenterol. 2003; 37(2):105-118. doi: 10.1097/00004836-200308000-00004.
  3. Johnston BC, Ma S, Goldenberg JZ, et al. Probiotics for the prevention of Clostridium difficile-associated diarrhea: A systematic review and meta-analysis. Ann Intern Med. 2012; 157(2):878-888. doi: 10.7326/0003-4819-157-12-201212180-00563.
  4. Hempel S, Newberry SJ, Maher AR, et al. Probiotics for the prevention and treatment of antibiotic-associated diarrhea: A systematic review and meta-analysis. JAMA. 2012; 307(18):1959-1969. doi: 10.1001/jama.2012.3507.
  5. Ford AC, Quigley EM, Lacy BE, et al. Efficacy of prebiotics, probiotics, and synbiotics in irritable bowel syndrome and chronic idiopathic constipation: Systematic review and meta-analysis. Am J Gastroenterol. 2014; 109(10):1547-1561. doi: 10.1038/ajg.2014.202.
  6. Lei WT, Shih PC, Liu SJ, et al. Effects of probiotics and prebiotics on immune response to influenza vaccination in adults: A systematic review and meta-analysis of randomized controlled trials. Nutrients. 2017; 9(11):E1175. doi: 10.3390/nu9111175. 
  7. Government of Canada. Canadian Antimicrobial Resistance Surveillance System (CARSS) report 2022. [Internet] 2023. [cited February 2023]. Available from:
  8. Oake N, Taljaard M, van Walraven C, et al. The effect of hospital-acquired Clostridium difficile infection on in-hospital mortality. Arch Intern Med. 2010; 170(2):1804-1810. doi: 10.1001/archinternmed.2010.405.
  9. Lewis, S. Probiotics and prebiotics: What’s the difference? [Internet] 2023. [cited February 2023]. Available from
  10. Institute for Health Metrics and Evaluation. Upper respiratory infections — Level 3 cause. [Internet] 2023. [cited February 2023]. Available from

DISCLAIMER: These summaries are provided for informational purposes only. They are not a substitute for advice from your own health care professional. The summaries may be reproduced for not-for-profit educational purposes only. Any other uses must be approved by the McMaster Optimal Aging Portal (

Many of our Blog Posts were written before the COVID-19 pandemic and thus do not necessarily reflect the latest public health recommendations. While the content of new and old blogs identify activities that support optimal aging, it is important to defer to the most current public health recommendations. Some of the activities suggested within these blogs may need to be modified or avoided altogether to comply with changing public health recommendations. To view the latest updates from the Public Health Agency of Canada, please visit their website.