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Probiotics and Infantile Colic: When Do They Actually Help?

Infantile colic can turn the first months of parenthood into hours of unexplained evening crying. An individual patient data meta-analysis of 4 trials (345 infants) found that the strain Lactobacillus reuteri DSM 17938 significantly shortens crying time — but the effect was clear only in breastfed infants, not in those fed formula.

AKdr Anna KowalczykSeptember 2, 202612 min read
Table of contents

TL;DR — key takeaways

Infantile colic — common, exhausting, and still not fully understood

Infantile colic is the common term for episodes of intense, hard-to-soothe crying in infants, classically defined by the "rule of threes": crying for more than 3 hours a day, more than 3 days a week, for more than 3 weeks, in an otherwise healthy, thriving infant. Even though colic is a self-limiting phenomenon — resolving on its own in the vast majority of infants by 3-4 months of age — for parents who have to live through it evening after evening, it's one of the most exhausting experiences of the first months of parenthood.

The exact cause of colic isn't fully understood, but one hypothesis under study is the role of an immature or disrupted infant gut microbiota — hence the interest in probiotics as a potential intervention. Among the strains studied, the most data has accumulated on Lactobacillus reuteri DSM 17938, making it a good starting point for assessing whether "probiotics for colic" is actually a confirmed strategy or just a popular belief.

What the 2018 individual patient data meta-analysis showed

Lactobacillus reuteri to Treat Infant Colic: A Meta-analysis

Strong evidence

Sung V, D'Amico F, Cabana MD et al. · Pediatrics · 2018

An individual participant data (IPD) meta-analysis of 4 double-blind randomized trials, covering a total of 345 infants with colic (174 in the probiotic group, 171 in the placebo group). The group receiving Lactobacillus reuteri DSM 17938 cried and/or fussed significantly less than the placebo group at all time points (adjusted mean difference in change from baseline at day 21: -25.4 minutes, 95% CI: -47.3 to -3.5). The probiotic group was almost twice as likely to achieve treatment success as the placebo group (adjusted incidence ratio at day 21: 1.7; 95% CI: 1.4-2.2). The intervention's effect was pronounced in breastfed infants (number needed to treat for day-21 success — NNT — was 2.6; 95% CI: 2.0-3.6), but was not statistically significant in formula-fed infants, where the authors judged the available data insufficient to draw conclusions.

View study

An NNT of 2.6 in breastfed infants means that, on average, giving the probiotic to fewer than three infants yields one treatment success that wouldn't have occurred with placebo alone — a very good result by the standards of clinical interventions, where an NNT in the teens or even higher is often still considered clinically valuable.

Breastfeeding vs. formula feeding is a crucial split in this data

This is one of the rare instances in pediatric literature where an infant's feeding method so clearly differentiates an intervention's effectiveness. The authors explicitly note that data on formula-fed infants were too limited to draw reliable conclusions — that's not the same as proof of no effect, but it's certainly not grounds to expect the same effect as in breastfed infants.

Why an individual patient data meta-analysis is stronger evidence

IPD is the gold standard for combining results across studies

Strong evidence

Unlike a classic meta-analysis, which pools already-published, aggregated results from individual studies, an individual participant data (IPD) meta-analysis analyzes the raw data of every single child from all included studies simultaneously, within one consistent statistical model. This allows for more accurate subgroup analysis (e.g., breastfed vs. formula-fed) and typically produces more reliable, precise effect estimates than combining published summaries alone. This is one reason this study is rated as strong evidence, even though it's based on "only" 4 primary trials.

Earlier meta-analyses of L. reuteri and colic, based on traditional pooling of aggregated results, gave a somewhat more mixed picture — partly precisely because they couldn't analyze the difference between breastfed and formula-fed infants as precisely. The IPD approach largely resolved this earlier inconsistency in results.

Why feeding method might change probiotic effectiveness

A mechanism that could explain the difference in effectiveness between breastfed and formula-fed infants likely relates to differences in the composition and maturity of gut microbiota between these two groups. Breast milk contains its own beneficial bacteria and oligosaccharides that support the growth of specific bacterial strains in the infant gut, which may create an environment where the administered probiotic more easily "takes hold" and produces a clinical effect.

This is still a mechanistic hypothesis, not a fully confirmed, precisely described mechanism — but it's consistent with the broader picture emerging from infant microbiota research, in which feeding method consistently proves to be one of the strongest factors shaping gut bacterial composition in early life.

Myth vs. fact

Myth

Probiotics are a proven, universal solution for infantile colic that will work for any baby regardless of whether they're breastfed or formula-fed.

Fact

The strongest available data (IPD meta-analysis, 345 infants) show a clear, clinically meaningful effect specifically in breastfed infants. For formula-fed infants, there isn't enough data to claim the probiotic works equally well — an important distinction that's easy to lose in oversimplified, marketing-driven messaging about probiotics for colic.

What to know before reaching for a probiotic

Practical tips for parents of a colicky infant

  • The strongest evidence concerns a specific strain — Lactobacillus reuteri DSM 17938 — not probiotics in general; other strains or blends don't necessarily have equivalent data
  • The effect is best documented in breastfed infants — for formula-fed infants, it's worth discussing realistic expectations with a pediatrician
  • Consult a pediatrician before starting any supplementation in an infant, especially to rule out other, more serious causes of excessive crying
  • In the cited study, effects were assessed up to day 21 of use — a short, few-day trial may not give a complete picture of potential benefit
  • Colic usually resolves on its own by 3-4 months of age regardless of treatment used, which is worth keeping in mind when assessing "what actually helped"

Limitations of this evidence

What this meta-analysis doesn't settle

The meta-analysis covered 4 studies and 345 infants — solid by pediatric research standards, but still a limited number of primary source studies. Data on formula-fed infants are, as the authors themselves emphasize, insufficient to draw conclusions in either direction — an area requiring further, dedicated research. The meta-analysis also didn't assess long-term effects of probiotic treatment beyond the observation period, nor did it directly compare different probiotic strains against each other.

QuestionShort answer
Does L. reuteri shorten crying with colic?Yes, significantly in breastfed infants (-25.4 min difference at day 21)
How large is the effect in breastfed infants?NNT=2.6 — a very good result for a clinical intervention
Does it also work in formula-fed infants?Insufficient data to confirm or rule this out
Is this strong evidence?Yes — an individual patient data meta-analysis of 4 RCTs, considered a strong type of evidence
Does the probiotic replace a pediatrician's consultation?No — excessive infant crying should always first be discussed with a pediatrician

Probiotics (L. reuteri DSM 17938) and colic at a glance

Our editorial recommendation

Infantile colic is one of those topics where desperate, sleep-deprived parents easily reach for the first available pharmacy solution. The good news is that with Lactobacillus reuteri DSM 17938, we have one of the rarer situations in pediatrics where a probiotic intervention has real, well-measured support from solid research — provided the infant is breastfed.

This is a rare case where parents' popular belief ("a probiotic will help with colic") actually lines up with solid scientific data — but only for a specific strain and a specific feeding method. It's worth knowing this detail rather than expecting a miracle from a random probiotic off the shelf.

Dr. Anna Kowalczyk, VitMode editorial team

Frequently asked questions

The most and strongest data concern the strain Lactobacillus reuteri DSM 17938, assessed in an individual patient data meta-analysis covering 4 studies and 345 infants. Other probiotic strains or blends don't necessarily have comparably strong data for this specific indication.

The meta-analysis didn't find sufficient data to confirm this — the effect was statistically insignificant or unassessed in this subgroup due to limited participant numbers. This isn't proof the probiotic definitely doesn't work in these infants, but there's also no basis to expect the same effect as in breastfed infants.

In the cited meta-analysis, effects were assessed up to day 21 of use, with a difference from placebo already visible within that period. A shorter, few-day trial may not give a complete picture of potential benefit.

In the vast majority of infants, colic resolves on its own by 3-4 months of age regardless of treatment. The meta-analysis, however, compared the probiotic to placebo over the same time period, so the observed difference favoring the probiotic isn't explained solely by natural symptom resolution.

Yes, definitely. Excessive, prolonged infant crying can have other, more serious causes besides functional colic, which a pediatrician should rule out before starting any supplementation, including probiotics.

An individual patient data (IPD) meta-analysis analyzes the raw data of every participant from all included studies within one consistent statistical model, allowing for more accurate subgroup analysis, such as feeding method. A regular meta-analysis combines already-aggregated, published results from individual studies, giving a less precise picture of differences between patient subgroups.

Lactobacillus reuteri DSM 17938 was generally well tolerated in clinical trials involving healthy infants, but any supplementation in an infant, especially one born prematurely or with other health issues, is worth discussing with a pediatrician beforehand.

Sources

AK

dr Anna Kowalczyk

PhD in Molecular Biology (University of Warsaw), 8 years researching cellular aging

Anna oversees the editorial process and scientific review of every publication in the knowledge base. She previously researched autophagy and mitochondrial biology.

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Comments (2)

  • KW

    Kasia W. 2 weeks ago

    Very clearly explained, especially the interactions section — I hadn't seen it laid out this well anywhere else.

  • MT

    Marek T. a month ago

    Are you planning to update this with the newest study from this year? I saw an interesting meta-analysis.