Lactobacillus reuteri is a species of probiotic, or “good” bacteria, that has co-evolved with mammals for millions of years. It is a natural inhabitant of the gastrointestinal tract in humans and many other animals. It is part of the gut microbiome. Like other probiotics, L. reuteri is not a single entity; it exists as various strains, each with distinct genetic profiles and characteristics. These differences mean that the effects observed with one specific strain cannot be assumed for another.
The Natural Role of Lactobacillus Reuteri
As a natural resident of the human body, Lactobacillus reuteri is found in several specific locations, most notably the gastrointestinal tract, the oral cavity, and in the breast milk of some mothers. In these environments, it contributes to maintaining a balanced microbial community. Its presence helps to occupy space and consume nutrients that might otherwise be used by potentially harmful microorganisms, creating a competitive environment that supports microbial diversity.
A function of certain L. reuteri strains is the production of a unique antimicrobial compound called reuterin. This substance is generated from glycerol, a compound found in food and also produced within the gut. Reuterin has a broad spectrum of activity, capable of inhibiting the growth of various bacteria, fungi, and protozoa. This production of antimicrobial substances is a primary mechanism by which L. reuteri helps to regulate the local microbial landscape and support the host’s natural defenses.
Researched Health Applications
These applications are highly dependent on the specific strain of the bacterium used, as different strains interact with the body in unique ways. Research has focused on areas ranging from infant health and digestive comfort to oral hygiene and immune system interaction.
A well-studied application is managing colic in breastfed infants. The strain L. reuteri DSM 17938 has been the subject of numerous clinical trials. Multiple studies have shown that administering this specific strain can significantly reduce daily crying time compared to a placebo. The mechanism is thought to involve the modulation of gut motility and the reduction of intestinal inflammation, leading to greater comfort for the infant. These benefits are most consistently observed in exclusively breastfed infants.
For digestive health, certain strains can help manage infectious diarrhea, particularly in children, by shortening its duration. It has also been investigated for its potential to prevent antibiotic-associated diarrhea, a common side effect of antibiotic therapy. Furthermore, some research points to its usefulness in alleviating functional abdominal pain, a condition common in children.
L. reuteri has also shown promise for the oral cavity. Research indicates that specific strains of L. reuteri can compete with cavity-causing bacteria, most notably Streptococcus mutans. Studies have demonstrated that the use of lozenges or tablets containing L. reuteri can lead to a reduction in the levels of S. mutans in saliva and plaque. Additionally, some clinical trials have reported that these probiotics can reduce gum bleeding and inflammation associated with gingivitis.
L. reuteri also interacts with the immune system. The gut is a major site of immune activity, and the bacteria residing there can influence immune responses both locally and systemically. Certain strains, such as L. reuteri ATCC PTA 6475, have been studied for their immunomodulatory properties. Research suggests these strains can influence the activity of various immune cells and the production of signaling molecules called cytokines. This interaction may help promote a balanced immune response.
Sources and Supplementation
While Lactobacillus reuteri is a natural human microbe, its presence has diminished in many individuals due to modern lifestyle factors, including diet. Obtaining it from food sources today is inconsistent. It is found in some traditional fermented products, such as certain types of sourdough, miso, and sauerkraut, as well as some dairy and meat products. However, the specific strains and their concentrations in these foods are not standardized, making them an unreliable source for a targeted dose.
For a consistent amount, supplements are the most dependable option. Probiotic products containing L. reuteri are widely available in various forms, including capsules, chewable tablets, and liquid drops. These supplements are manufactured under controlled conditions to ensure a specific quantity of live bacteria, measured in Colony Forming Units (CFUs), is present in each dose.
A product label should identify the exact strain used, as this determines its researched application. For example, L. reuteri DSM 17938 is the strain extensively studied for infantile colic and digestive health. In contrast, L. reuteri ATCC PTA 6475 is a strain that has been investigated for its effects on the immune system.
Dosage can vary depending on the product and the intended purpose. Doses in clinical studies range from 100 million to several billion CFUs per day. Consumers should always adhere to the dosage instructions provided by the manufacturer on the product label. Consulting with a healthcare professional is recommended before starting a new supplement.
Safety and Considerations
Lactobacillus reuteri is broadly considered safe for consumption by the general healthy population. Strains intended for use in food and supplements have been designated as Generally Recognized as Safe (GRAS) by regulatory bodies like the U.S. Food and Drug Administration. This status is based on a long history of safe use and scientific evaluation.
When first introducing the probiotic, some individuals may experience mild and temporary digestive changes. This can include increased gas or bloating. These side effects are uncommon and resolve within a few days. Most clinical trials, including those involving infants and children, report no significant adverse events associated with L. reuteri supplementation.
Despite its strong safety profile, certain populations should exercise caution. Individuals with compromised immune systems, such as those with HIV/AIDS or undergoing chemotherapy, should consult a doctor before using probiotics. People with serious underlying medical conditions, such as short bowel syndrome, or those with central venous catheters are also advised to seek medical guidance.
The use of L. reuteri in specific life stages also warrants consideration. While it has been safely used in many studies involving infants, this should always be done in consultation with a pediatrician. Similarly, pregnant or breastfeeding women should discuss the use of any supplement, including probiotics, with their healthcare provider.