In the past decade, probiotic supplement dosages have rocketed from millions to billions of CFUs, with some boasting as many as 200 billion. While more may be better when it comes to love and money, this is not necessarily —but can be — the case with probiotics.
CFUs or colony forming units: a unit of measure to estimate the number of bacteria in a sample capable of dividing and forming colonies.
So what is the best number? As is usual in the world of microbiology, the answer is complicated.
First, the globally accepted definition of a probiotic is sweeping in scope, and as we shall see, for good reason.
“Live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.”
In the definition of probiotics, the phrase “when administered in adequate amounts” can be ambiguous and sometimes drive consumers and healthcare practitioners to choose a supplement with many billions of CFUs. In this context, “adequate” is variable: a lower dose may work as well or even better than a higher dose, depending on the condition or disorder for which it is being used.
Most importantly, the dose should match the CFU level shown in an efficacy study to endow a benefit. Therefore, an individual’s purpose for taking probiotics will determine the dose.
To be probiotic, live microorganisms must be scientifically justified on a strain-by-strain basis and supported by peer reviewed clinical trials to benefit health. Fermented foods and beverages such as kimchi, kombucha and kefir may contain live microorganisms buttypically do not meet the required evidence level for probiotics, since their health effects have not been confirmed or linked to the microbes in the product and the mixtures may be largely uncharacterized. Therefore, strain designation is crucial; different strains of the same species may imbue different health effects.
Researchers have sought to determine if an effective dose-response for probiotics could be established for specific conditions, much like is calibrated for pharmaceutical drugs.
One disorder investigated to that end is antibiotic-associated diarrhea (AAD). When antibiotics are prescribed for children, the gut microbiota is altered resulting in AAD. Probiotics may restore the microbiota, preventing diarrhea.
A number of reviews and meta-analyses explored whether dose of probiotics had to meet a threshold to be effective.
A 2015 analysis of 22 studies determined that probiotic doses ≥ 5 x 109 cfu/day (5 billion CFUs) were more effective in preventing AAD than lesser doses. Various probiotics and combinations were used however, making recommendations difficult.
A 2017 review of dose-response from seven meta-analyses of probiotics for reducing risk for AAD found a 1010 cfu/day (10 billion) to be the break point for effectiveness.
This review also reported a meta-analysis which observed that higher doses (>1011cfu/day/ 100 billion) of probiotics were more effective than lower doses in blood pressure reduction. Probiotics have other established indications such as Clostridium difficile infections, necrotizing enterocolitis, prevention of atopic dermatitis, prevention of colorectal cancer, or the treatment of irritable bowel syndrome. Reviewer Artur Ouwehand PhD found no clear dose-response in these but concluded: “The lack of a clear dose-response for other end-points does not mean it does not exist; present data does just not allow drawing any conclusions.”
Many consumers will be interested in what will be “adequate” or the effective dose for general health, bowel function and immune strength. No clear dose-response relations were exhibited in the investigations. In the future, we might learn that the “effective dose” will also be strain specific.
Probiotic CFUs on Labels
IPA with the Council for Responsible Nutrition advises manufacturers to list the total number of CFUs —by strain ideally —at the end of the stated shelf life or “use by” date, not at the time of manufacture. Declines in CFUs may occur over the product’s shelf life and prudent manufacturers will take this into account when formulating their product.
Because probiotic characteristics are strain specific, the choice will depend on an individual’s purpose for taking probiotics. The dose or CFU count should match the CFU level shown in an efficacy study to endow a benefit. One size certainly doesn’t fit all, making a broad recommendation of what is adequate virtually impossible. However, several conditions including AAD and high blood pressure show positive correlation between dose of probiotics and benefit.
Goldenberg, Joshua Z et al. “Probiotics for the prevention of pediatric antibiotic-associated diarrhea.” The Cochrane database of systematic reviews, 12 CD004827. 22 Dec. 2015, doi:10.1002/14651858.CD004827.pub4
Sniffen, Jason C et al. “Choosing an appropriate probiotic product for your patient: An evidence-based practical guide.” PloS one vol. 13, 12 e0209205. 26 Dec. 2018, doi:10.1371/journal.pone.0209205
Treven, P. “Strategies to develop strain-specific PCR based assays for probiotics.” Beneficial microbes vol. 6,6 (2015): 887-98. doi:10.3920/BM2015.0009
Ouwehand, A C. “A review of dose-responses of probiotics in human studies.” Beneficial microbes vol. 8, 2 (2017): 143-151. doi:10.3920/BM2016.0140