Should I refrigerate probiotics?
Read the label, and expect it to disagree with the website — in one case in our set it does, on both storage and potency basis. Measured magnitudes: after 90 days, 4.2–5.3 log CFU/g refrigerated versus 2.6–4.9 log CFU/g at room temperature.
One product in this audit contradicts itself, on both counts
A label and its own website contradict each other on both potency basis and storage. The label footnote, verbatim: "▲ 60 billion CFU at time of manufacture through best by date when stored properly. Best stored refrigerated." The website, verbatim: "With no refrigeration required, this Probiotic blend of 60 Billion CFU is guaranteed through the expiration date, not the manufacturing date like most probiotic brands on the market." Both surfaces belong to the same company and the same product, and they disagree about what you have to do to get what you paid for.
What storage is actually worth, measured
After 90 days: 4.2±0.1 to 5.3±0.2 log CFU/g refrigerated versus 2.6±0.3 to 4.9±0.2 log CFU/g at room temperature. A freeze-dried synbiotic held 8–9 log CFU/g through 90 days refrigerated, with "considerable reduction" at 25±1 °C. In three commercial probiotic yoghurts, "only 53.8% of the CFU remained after 6 h at RT; after 24 h, only about one fourth of the CFU were found." Species differ from each other by 2–3 log under similar conditions, so none of this transfers cleanly from one product to another (PMID 31936726 (opens in a new tab); PMID 24426051 (opens in a new tab); PMID 28763015 (opens in a new tab)).
Which is why the potency basis matters more than the storage instruction. ISAPP, verbatim: "The label may state that the count is 'at time of manufacture', a number that is no doubt inadequate if you purchase the product close to the end of its shelf-life." ESPGHAN takes the end-of-shelf-life position and notes that "inconsistencies and deviations… are surprisingly common" (PMID 28644359 (opens in a new tab)). A refrigeration instruction on a bottle that only guarantees its count at the factory gate is asking you to protect a number nobody has promised you.