“10 billion CFU” is one of the most common numbers on a probiotic label. It sounds precise. But there’s a question the number alone doesn’t answer: 10 billion when?
Probiotics are alive, and they don’t stay that way forever
CFU stands for colony-forming units, a count of live microorganisms that can grow. That is what makes probiotics different from most supplement ingredients. A vitamin C tablet doesn’t “die” on the shelf. Probiotic bacteria do, slowly, from the day the product is made.
Three things speed up that loss:
- Heat. Warm storage, hot warehouses and summer shipping all cut viability.
- Moisture. Many probiotic strains are very sensitive to water. A small rise in humidity inside the bottle can make a big difference.
- Time. Even in good conditions, counts fall over the shelf life.
“At manufacture” vs “at end of shelf life”
A label that says “10 billion CFU at time of manufacture” is telling you the count on the day it was made. By the time the bottle is opened months later, the real count can be much lower.
A label that says “10 billion CFU through expiration” or “at end of shelf life” is making a stronger promise: the product should still have at least that many live cells on its last good day. That is the wording industry groups recommend. The International Probiotics Association and the Council for Responsible Nutrition both encourage brands to guarantee CFU through the end of shelf life, not at manufacture.
The FDA also changed its position. Supplement labels must list ingredient amounts by weight, but FDA guidance finalized in 2022 says the agency won’t object if live microbials are also declared in CFU. That’s why CFU numbers are now standard on US labels.
Independent tests have found gaps
Independent labs that buy products off the shelf have, over the years, found some probiotics with fewer live cells than their labels claim. Not all products, and not most, but enough that the wording on the label matters.
What consumers can check
- Look for “through expiration” or “at end of shelf life” next to the CFU number.
- Store the bottle the way the label says. If it says refrigerate, refrigerate.
- Keep the lid closed and the desiccant in, and don’t store it in a steamy bathroom.
What this means for brands making a probiotic
Promising a CFU count at end of shelf life is a manufacturing decision, not just a label decision. It usually involves:
- Overage. Formulating with more live cells than the label claim, to cover expected loss over the shelf life.
- Strain choice. Some strains hold up far better at room temperature than others.
- Moisture control. Low-moisture excipients, controlled production rooms, and packaging such as desiccant bottles or blister packs.
- Stability testing. Counting CFU at set points across the shelf life to back up the claim with data.
- Storage instructions that match reality. If the product needs refrigeration to hold its count, the label and the supply chain both have to say so.
These choices affect cost. But a probiotic that meets its number on the last day is the one that survives a customer’s own lab test, and a retailer’s.
The takeaway
A big number at the factory isn’t a promise. The honest CFU claim is the one that still holds at the end of shelf life.
Sources
- US FDA, Guidance for Industry: Policy Regarding Quantitative Labeling of Dietary Supplements Containing Live Microbials (draft 2018, final 2022).
- International Probiotics Association, Best Practices Guidelines for Probiotics; Council for Responsible Nutrition, Best Practices Guidelines for Probiotics (CFU guaranteed through end of shelf life).
- Independent product testing reviews of probiotic supplements (e.g., ConsumerLab).