Lactobacillus reuteri is one of the most studied probiotics: infant colic, bones, the stomach, gums… Yet this name covers very different strains, and results obtained with one do not apply to others. Here is what studies actually show, strain by strain, including the doses used, negative findings, safety and what European regulations allow us to say.
Key takeaways
- Since 2020, Lactobacillus reuteri has officially been called Limosilactobacillus reuteri, following the reclassification of the Lactobacillus genus.
- Results depend on the strain (DSM 17938, ATCC PTA 6475…) and cannot be transferred from one strain to another.
- The strongest evidence concerns colic in breastfed infants; for bone, two trials contradict each other.
- No health claim is authorised for probiotics in the European Union.
What is Lactobacillus reuteri?
It is a lactic acid bacterium that naturally lives in the intestines of humans and many animals. It is among the species used as probiotics: live microorganisms studied for a health benefit when consumed in sufficient amounts.
In 2020, an international team revised the classification of the Lactobacillus genus, which had become too heterogeneous with 261 species. It split the group into 25 genera based on complete genomes. Lactobacillus reuteri thus became Limosilactobacillus reuteri. The old name remains widely used on labels and in online searches: it is the same species.
Why does the strain make all the difference?
A bacterial species includes many strains with different genomes and properties, somewhat like breeds within an animal species. Each studied strain has its own designation of letters and numbers: DSM 17938, ATCC PTA 6475, ATCC PTA 5289 or NCIMB 30242 for L. reuteri.
A systematic review of 228 trials confirmed this in 2018: probiotic efficacy depends on both the strain and the situation studied. A strain effective in one context may do nothing in another, and two strains of the same species can produce different results. Grouping “all L. reuteri” under one promise therefore makes no sense.
Infant colic: the strongest evidence
DSM 17938 is the strain most studied in infants. An individual participant data meta-analysis pooled 4 double-blind trials involving 345 babies with colic. After 21 days, the probiotic group cried or fussed an average of 25 minutes less per day than the placebo group. The effect was clear in breastfed babies, but non-significant in formula-fed babies because of insufficient data. Several authors declared links to the strain manufacturer outside this work.
The picture is not uniform. In an Australian community trial involving 167 infants with colic, breastfed or not, 100 million CFU daily for one month provided no benefit: at one month, babies in the probiotic group even cried or fussed 49 minutes more per day, particularly formula-fed babies.
Giving a probiotic from birth to prevent colic is even less established. A Cochrane review of 6 trials (1,886 newborns) found no clear evidence of a reduction in colic cases, with low certainty. Crying duration was reduced by 44 minutes daily in L. reuteri trials, but these findings are highly heterogeneous.
Bone loss: one positive trial, one negative trial
Strain ATCC PTA 6475 has been tested for bone. In Sweden, 90 women aged 75 to 80 with low bone density received 10 billion CFU per day or placebo for one year. Tibial density loss was around 0.8% with the probiotic versus 1.9% with placebo, a difference of around 1 percentage point. Other bone measures moved in the same direction without reaching significance.
The same team sought to confirm the result. In 239 women aged 50 to 60 in early menopause, 1 or 10 billion CFU daily for two years had no effect on bone loss or bone turnover markers. This trial was partly funded by the strain manufacturer.
For bone, authorised claims concern nutrients: “Calcium is needed for the maintenance of normal bones”, “Vitamin D contributes to the maintenance of normal bones”, “Magnesium contributes to the maintenance of normal bones”. We compare forms of the latter in our comparison of magnesium forms.
Helicobacter pylori: studied alongside treatment, without replacing it
Helicobacter pylori is a stomach bacterium whose eradication relies on a combination of antibiotics prescribed by a doctor. Probiotics have been studied as an addition to this treatment. A meta-analysis of 11 randomised trials involving 724 patients found a slightly higher eradication rate when lactobacilli were added (relative risk 1.16). For the L. reuteri subgroup, the relative risk was 1.18, whereas the tested L. rhamnosus strain performed no better than control. Treatment-related taste disturbances were also less frequent.
The gain remains modest, and strains, doses and durations varied between trials. A probiotic never replaces antibiotics.
Periodontitis: a modest, short-lived effect in trials
For periodontitis, inflammation of the tissues supporting the teeth, lozenges combining strains DSM 17938 and ATCC PTA 5289 have been tested after deep cleaning. In a trial involving 30 patients, one lozenge morning and evening for 12 weeks, containing 100 million CFU of each strain, reduced moderate and deep periodontal pocket depths more than placebo. The study was partly manufacturer-funded.
A meta-analysis of 11 trials confirmed a modest benefit: around 0.6 mm less pocket depth at 3 weeks and 0.4 mm at 3 months, an effect the authors considered short-lived. Here, the bacterium was studied in contact with the gums: a lozenge is not equivalent to a swallowed capsule, as we explain in our article on capsules, tablets and other forms.
Cholesterol: a strain-specific possibility
A meta-analysis of 6 trials (512 participants, 4 strains) observed a mean total cholesterol reduction of 0.26 mmol/L, with no overall effect on LDL, HDL, triglycerides, blood pressure or blood glucose. Only strain NCIMB 30242 reduced both total and LDL cholesterol. Other ingredients have been studied for blood lipids, such as berberine, discussed in our article on berberine.
What Lactobacillus reuteri doses have studies used?
Doses are expressed in CFU, “colony-forming units”: live bacteria capable of multiplying. They vary by a factor of 100 according to the strain and the question studied.
| Strain | Topic studied | Dose and duration | Result |
|---|---|---|---|
| DSM 17938 | Colic (4 trials) | 100 million CFU/day as drops, 21 days | Around 25 min less crying per day, especially if breastfed |
| DSM 17938 | Colic, community trial | 100 million CFU/day, 1 month | No benefit |
| ATCC PTA 6475 | Bone, women aged 75 to 80 | 10 billion CFU/day, 1 year | Bone loss reduced by around 1 percentage point |
| ATCC PTA 6475 | Bone, women aged 50 to 60 | 1 or 10 billion CFU/day, 2 years | No effect |
| DSM 17938 + ATCC PTA 5289 | Periodontitis | 2 lozenges/day, 12 weeks | Slightly shallower pockets |
| NCIMB 30242 | Cholesterol | Variable | Total and LDL cholesterol reduced |
Is Lactobacillus reuteri dangerous?
In the cited trials, adverse effects were no more frequent than with placebo. Infections caused by lactobacilli remain rare: a review of cases published between 2019 and 2021 identified 48, only one involving L. reuteri. They mainly affected people with diabetes or impaired immunity who had risk factors such as an artificial heart valve or recent dental care.
Premature infants are a separate case. After a premature infant died, the US Food and Drug Administration (FDA) warned in 2023 that probiotics given to hospitalised premature infants expose them to serious, sometimes fatal infections. Seek medical advice before any probiotic in cases of impaired immunity, serious illness, a central catheter or for a newborn.
What do European regulations say?
No health claim has been authorised for a probiotic in the European Union. The Commission even considers the word “probiotic” alone an implied health claim. The only claim relating to live bacteria concerns yoghurt cultures and lactose digestion, not L. reuteri. A supplement containing L. reuteri therefore cannot claim any effect: the studies described here are research, not a product promise.
Frequently asked questions
How do you read a strain name?
The letters DSM, ATCC or NCIMB identify the culture collection that holds the strain, in Germany, the United States or the United Kingdom, followed by a number. Without this designation on the label, it is impossible to link a product to a specific study.
Which foods contain L. reuteri?
It is not a conventional yoghurt culture; yoghurt is made with Streptococcus thermophilus and Lactobacillus bulgaricus. It is mainly found in human and animal intestines. Some fermented dairy products are nevertheless enriched with specific strains.
Does Lactobacillus reuteri help with weight loss?
None of the trials presented here studied weight: there is no basis to say it causes weight loss. Other approaches have been explored for sugar cravings, such as gymnema, discussed in our article on gymnema and sugar cravings.
Can L. reuteri be given to a baby?
Colic studies used drops dosed for infants, not adult capsules. Ask a paediatrician for advice before any use, and never give it to a premature infant without medical supervision.
How long should it be taken?
Trials lasted from 3 weeks for colic to 12 weeks for gums, and up to 2 years for bone. There is no universal duration: it depends on the strain and the question studied.
Have homemade L. reuteri yoghurts been proven effective?
These preparations, popular online, were not evaluated in the trials cited here. The actual strain and quantity of live bacteria are unknown, and production hygiene is not controlled.
L. reuteri or L. rhamnosus: which should you choose?
The question concerns the strain, not the species. In the Helicobacter pylori meta-analysis, L. reuteri strains improved eradication; the tested L. rhamnosus strain did not. On another topic, the ranking might be reversed.
Conclusion
Lactobacillus reuteri is not one probiotic but a family of strains with mixed results. Strain DSM 17938 has the strongest data, in breastfed infants with colic; effects on bone, the stomach, gums or cholesterol remain modest, occasional or conflicting. Before drawing conclusions from a study, check the strain, dose, population and duration. Remember that no health claim is authorised for probiotics in the European Union.
Sources
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- McFarland LV, Evans CT, Goldstein EJC (2018). Strain-Specificity and Disease-Specificity of Probiotic Efficacy: A Systematic Review and Meta-Analysis. Front Med, 5, 124. doi:10.3389/fmed.2018.00124
- Sung V et al. (2018). Lactobacillus reuteri to Treat Infant Colic: A Meta-analysis. Pediatrics, 141(1), e20171811. doi:10.1542/peds.2017-1811
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- Ong TG et al. (2019). Probiotics to prevent infantile colic. Cochrane Database Syst Rev, 3, CD012473. doi:10.1002/14651858.CD012473.pub2
- Nilsson AG et al. (2018). Lactobacillus reuteri reduces bone loss in older women with low bone mineral density: a randomized, placebo-controlled, double-blind, clinical trial. J Intern Med, 284(3), 307-317. doi:10.1111/joim.12805
- Gregori G et al. (2024). Limosilactobacillus reuteri 6475 and Prevention of Early Postmenopausal Bone Loss: A Randomized Clinical Trial. JAMA Netw Open, 7(6), e2415455. doi:10.1001/jamanetworkopen.2024.15455
- Yu M et al. (2019). Efficacy of Lactobacillus-supplemented triple therapy for H. pylori eradication: A meta-analysis of randomized controlled trials. PLoS One, 14(10), e0223309. doi:10.1371/journal.pone.0223309
- Teughels W et al. (2013). Clinical and microbiological effects of Lactobacillus reuteri probiotics in the treatment of chronic periodontitis: a randomized placebo-controlled study. J Clin Periodontol, 40(11), 1025-1035. doi:10.1111/jcpe.12155
- Song D, Liu XR (2020). Role of probiotics containing Lactobacillus reuteri in adjunct to scaling and root planing for management of patients with chronic periodontitis: a meta-analysis. Eur Rev Med Pharmacol Sci, 24(8), 4495-4505. doi:10.26355/eurrev_202004_21032
- Liu J et al. (2023). Limosilactobacillus reuteri consumption significantly reduces the total cholesterol concentration without affecting other cardiovascular disease risk factors in adults: A systematic review and meta-analysis. Nutr Res, 117, 1-14. doi:10.1016/j.nutres.2023.06.004
- Rossi F et al. (2022). Lactobacilli Infection Case Reports in the Last Three Years and Safety Implications. Nutrients, 14(6), 1178. doi:10.3390/nu14061178
- U.S. Food and Drug Administration (2023). Risk of Invasive Disease in Preterm Infants Given Probiotics Formulated to Contain Live Bacteria or Yeast. 29 September 2023. fda.gov
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Food supplements do not replace a varied, balanced diet or a healthy lifestyle. Ask a healthcare professional for advice if you are taking medication, pregnant or breastfeeding.
