Big effect
A probiotic slashed HbA1c by 0.5% more than placebo in a 40-person trial — but only in people with diabetes and gum disease, and it did nothing for the gum infection itself.
This is an early, small signal that *L. reuteri* might improve blood sugar control in a specific clinical population, but the lack of effect on the gum disease it was supposed to treat means the metabolic benefit is a side finding, not a proven standalone effect.
In a 6-month trial of 40 people with both diabetes and periodontitis, adding L. reuteri probiotics to standard gum treatment led to a 0.5% greater drop in HbA1c (a key blood sugar marker) compared to placebo. However, the probiotic did not improve gum pocket depth or reduce harmful bacteria in the mouth, so the blood sugar improvement stands alone — and may not apply to people without gum disease or to those taking the probiotic without concurrent dental treatment.
Where this fits in the evidence
This is among the first studies we've indexed on Lactobacillus reuteri for Reduced Hemoglobin A1c — treat it as an early signal until more research accumulates.
The study
- Randomized Controlled Trial (RCT)
- n = 40
- 2025-09-17
- Journal of clinical periodontology
- PubMed: 40958659
- DOI: 10.1111/jcpe.70035
- Full study breakdown →
This is a plain-language summary of a research finding, not medical advice. Pillser surfaces research signals to help you decide what's worth investigating — always consult a qualified professional before changing what you take.