Lactobacillus reuteri
Limosilactobacillus reuteri (strains DSM 17938, ATCC PTA 6475, RC-14, ATCC 55730)
L. reuteri is a well-studied probiotic species with its best evidence in infant colic (strain DSM 17938), and promising trials in bone density, H. pylori, oral health and functional constipation.
At a Glance
- Best known for
- Reduces crying time in breastfed infants with colic (DSM 17938), Reduces bone loss in older women with low bone density (ATCC PTA 6475), Lowers H. pylori load and side effects of eradication therapy
- Evidence
- Moderate
- Typical dose
- 100 million CFU DSM 17938 (5 drops) once daily for 21 days
- Type
- Probiotic
What is Lactobacillus reuteri?
Lactobacillus reuteri (reclassified as Limosilactobacillus reuteri in 2020) is one of the few Lactobacillus species native to the human gut, breast milk and mouth, and is also found in many other mammals and birds, which suggests a long co-evolution with vertebrate hosts. It was named after German microbiologist Gerhard Reuter, who distinguished it in the 1960s. Different strains have been developed for different purposes: DSM 17938 (derived from the original ATCC 55730 by removing antibiotic-resistance plasmids) is the infant colic strain used in BioGaia drops; ATCC PTA 6475 is studied for bone, inflammation and oral health; RC-14 is paired with L. rhamnosus GR-1 for vaginal health. Studies on one strain do not necessarily apply to others.
Known Health Benefits
How It Works
L. reuteri produces reuterin, a broad-spectrum antimicrobial that inhibits pathogenic bacteria, yeasts and protozoa by inducing oxidative stress in them, without harming beneficial gut flora. It adheres to mucus and competes with pathogens for binding sites. Certain strains produce histamine that acts on H2 receptors to suppress TNF-α production, a notable anti-inflammatory mechanism, and they induce regulatory T cells and IL-10. In infant colic, DSM 17938 appears to reduce gut inflammation (lower fecal calprotectin), increase Lactobacillus abundance, reduce E. coli, and normalize gut motility and visceral pain signaling. The bone effect of ATCC PTA 6475 is thought to work through reduced gut-derived inflammation and TNF-α, which otherwise drives osteoclast activity, with animal studies showing increased bone formation. In the mouth, reuterin and competition suppress Streptococcus mutans and periodontal pathogens.
What Research Says
The colic evidence is the most robust. A 2018 individual-participant-data meta-analysis in Pediatrics pooled four double-blind RCTs (345 infants) and found L. reuteri DSM 17938 roughly halved crying time at 21 days in breastfed infants (about 25 minutes less daily crying), with a number needed to treat of about 3, though it did not help formula-fed infants and one large Australian trial was negative. For bone, a 2018 Swedish double-blind RCT of 90 older women found ATCC PTA 6475 halved tibial bone loss over 12 months compared with placebo, a single but well-designed trial. Meta-analyses show L. reuteri modestly increases H. pylori eradication rates and reduces therapy side effects. Trials of lozenges report reduced gingival bleeding and plaque. Smaller studies suggest benefit in functional constipation in infants and adults, infant regurgitation, and reduced infections in daycare. Evidence for cholesterol lowering (strain NCIMB 30242), vaginal health (RC-14) and sleep or testosterone (mouse studies) ranges from moderate to purely preclinical.
Active Compounds
Live Limosilactobacillus reuteri cells; reuterin (3-hydroxypropionaldehyde, antimicrobial), reutericyclin, histamine (strain-dependent, anti-inflammatory via H2 receptor), exopolysaccharides, vitamin B12 and folate
Forms & Bioavailability
L. reuteri tolerates gastric acid and bile reasonably well; many strains transiently colonize the gut for 1–2 weeks after stopping. The infant drops are an oil suspension and must be shaken well before use; potency depends on storage below 25°C. Lozenges allow the bacteria to colonize the oral cavity for local effects. As with all probiotics, effects are strain-specific and continued dosing is required for sustained benefit.
Dosage Guidance
| Use Case | Dosage |
|---|---|
| Infant colic (breastfed) | 100 million CFU DSM 17938 (5 drops) once daily for 21 days |
| Bone density (older women) | 10 billion CFU ATCC PTA 6475 daily |
| H. pylori adjunct | 100 million to 1 billion CFU 2x daily during and after triple therapy |
| Gum health | 1 lozenge (100–200 million CFU) 2x daily |
| Functional constipation (infants/adults) | 100 million CFU daily |
Always consult a healthcare provider for personalized dosing.
Natural Food Sources
- Human breast milk (natural source for infants)
- Some fermented meats and sourdough (strain-dependent, not reliable)
- Yogurts and dairy products labeled with L. reuteri
- Not reliably obtained from ordinary fermented foods
Potential Side Effects
Mild gas or bloating initially; rare bacteremia in immunocompromised or critically ill patients; no significant side effects in infant trials
Who Should Avoid It
- Severe immunosuppression or critical illness without medical supervision
- Central venous catheter
- Premature or very low birth weight infants (only NICU-supervised products)
- Histamine intolerance — some strains produce histamine (theoretical)
Pregnancy & Lactation
L. reuteri strains have been studied in pregnant women (for example to reduce infant allergy) and in breastfeeding mothers without safety problems, and the species is naturally present in breast milk. Infant drops are given directly to newborns from birth in trials with good tolerability. Use of specific strains during pregnancy for a purpose should still be discussed with a midwife or doctor.
Known Drug Interactions
Antibiotics reduce viability (separate by 2 hours); may enhance tolerance of H. pylori triple therapy (beneficial); theoretical risk with immunosuppressants; no interactions with common medications documented
Evidence Classification
Supported by cohort studies, case-control studies, or multiple observational studies with consistent findings.
Frequently Asked Questions
Does L. reuteri really help colic?
For breastfed babies, the pooled evidence from four trials shows about half as much crying after 3 weeks compared with placebo, which is a meaningful effect for exhausted parents. It did not help formula-fed babies in the one large trial that included them, and a few trials were negative. The drops are very safe, so a 3-week trial is reasonable after your pediatrician has ruled out other causes of crying.
Can a probiotic really protect bones?
One well-run Swedish trial found L. reuteri ATCC PTA 6475 halved bone loss over a year in women aged 75–80 with low bone density. The mechanism (reducing gut-driven inflammation that activates bone-resorbing cells) is plausible and supported by animal work. It is a single trial, so it is not a substitute for established osteoporosis treatment, but it is an interesting low-risk adjunct.
Which strain should I buy?
It depends on your goal: DSM 17938 for infant colic and digestive uses; ATCC PTA 6475 for bone, inflammation and oral health (often combined with DSM 17938 in lozenges); RC-14 with L. rhamnosus GR-1 for vaginal and urinary health; NCIMB 30242 for cholesterol. Look for the strain designation on the label rather than just the species name.
I read that L. reuteri boosts testosterone and social behavior — is that true?
Those findings come from mouse studies, where L. reuteri increased testosterone, testicular size and social behavior in autism models via the vagus nerve and oxytocin. No human trials have confirmed hormonal or behavioral effects, and the home-fermented 'L. reuteri yogurt' trend is based on this rodent work, not on human data.
References
- Lactobacillus reuteri to Treat Infant Colic: A Meta-analysis. Sung V, D'Amico F, Cabana MD, et al.. Pediatrics (2018)
- Lactobacillus reuteri reduces bone loss in older women with low bone mineral density: a randomized, placebo-controlled, double-blind, clinical trial. Nilsson AG, Sundh D, Bäckhed F, Lorentzon M. J Intern Med (2018)
- Role of Lactobacillus reuteri in Human Health and Diseases. Mu Q, Tavella VJ, Luo XM. Front Microbiol (2018)
- Probiotics — Health Professional Fact Sheet. NIH Office of Dietary Supplements. NIH ODS (2023)View study
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This entry is for educational purposes only. It is not medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement regimen, especially if you take medications or have health conditions.