For infant colic: standardized daily drops (DSM 17938). Adult: 4–10 billion CFU/day depending on the indication.
In premature neonates: −42% severe necrotizing enterocolitis and −65% all-cause mortality.
View the study (systematic review) →Encapsulated in nanoparticles and added to yogurt: −12% LDL and −9% total cholesterol in adults with hypercholesterolemia.
View the study (RCT) →Breastfed babies: reduces crying and fussing time; double the probability of treatment success vs placebo.
View the study (systematic review) →4 billion CFU for 6 months significantly reduced HbA1c versus placebo (6-month effect).
View the study (RCT) →⏱ 3 min read
Lactobacillus reuteri is one of the few bacteria of the genus Lactobacillus that humans harbor natively: it lives in the digestive tract and in breast milk, and its co-evolution with our species over hundreds of thousands of years explains why its safety profile is exceptional and why its effects on health, when its presence is restored, are much broader than one would expect from a simple probiotic.
The most clinically studied strain is DSM 17938, originally derived from the breast milk of a Peruvian woman in the 1980s, and hundreds of clinical trials in infants, children, and adults have been developed from it, revealing a profile of biological activity very different from that of generic probiotics: it produces reuterin (a broad-spectrum antimicrobial), strengthens the tight junctions of the intestinal epithelium, modulates the immune response, and releases molecules that communicate directly with the enteric nervous system.
Infant colic is one of the most exhausting experiences of the first months of life, and for decades medicine offered nothing with evidence beyond patience and physical contact; over the past fifteen years, several randomized trials with breastfed babies have shown that Lactobacillus reuteri reduces daily crying time in a statistically significant way, with a probability of treatment success twice that of placebo, an effect that is especially robust in breastfed infants.
The evidence is much weaker in formula-fed babies, where meta-analyses show no consistent effect, which suggests that part of the bacterium's activity depends on human milk oligosaccharides and on how they interact with the early infant microbiota; this nuance is important because it indicates that the biological context modulates efficacy, and it is not simply a matter of "taking the probiotic and waiting for the result."
One of the most striking findings in Lactobacillus reuteri research comes from neonatology: in preterm babies, in whom necrotizing enterocolitis is a devastating complication with mortality close to 30 percent, supplementation with probiotics that include this bacterium reduces the risk of severe enterocolitis by 42 percent and all-cause mortality by 65 percent, according to a large Cochrane review that synthesizes the available evidence.
These numbers are what have led several hospitals to incorporate probiotics as part of standard care for preterm infants, a medical decision that still requires individual risk assessment for each baby because severe immunosuppression or the presence of central venous catheters can increase the rare but serious risk of bacteremia, a complication that has led the FDA to issue specific warnings in vulnerable populations.
In adults with mild to moderate hypercholesterolemia, supplementation with Lactobacillus reuteri encapsulated in a matrix that protects the bacterium from gastric acid has shown reductions of 12 percent in LDL cholesterol and 9 percent in total cholesterol compared with placebo, a modest but clinically significant effect that adds to traditional interventions and is explained by the bacterium's ability to deconjugate bile salts in the intestine, altering the enterohepatic cycle of cholesterol.
In type 2 diabetes, a randomized trial with 4 billion colony-forming units daily for six months significantly reduced glycated hemoglobin compared with placebo, with a modest but relevant effect size because glycemic control is one of the strongest predictors of chronic diabetes complications and because the tool is inexpensive, safe, and compatible with any other standard treatment.
Not all products labeled Lactobacillus reuteri are equivalent: the specific strain, the matrix protecting against gastric acid, the viability of the bacterium at the end of the product's shelf life, and the dose in colony-forming units vary enormously between manufacturers, and most of the positive clinical trials were done with specific strains and formulations that are worth looking for on the label before spending money on a generic pharmacy product.
For use in infants, use exclusively strains with registered clinical evidence and under pediatric guidance; for adult use, the effective doses in trials are between 1 billion and 10 billion CFU daily, for at least three months to see changes in markers such as cholesterol or HbA1c, and always with the warning to avoid the product in people with severe immunosuppression or central venous catheters because of the rare risk of bacteremia.
Information, not medical advice. Scientific evidence reflects the quality of the studies.