Bifidobacterium longum

What it is

Bifidobacterium longum is a gut bacterium. Its subspecies infantis is unusually good at digesting the complex sugars in human milk. It is used in probiotic supplements, and effects differ by strain and subspecies.

What the research says

The strongest evidence is in preterm infants. A meta-analysis of 67 trials found probiotic products containing B. infantis linked to fewer cases of necrotising enterocolitis, with the GRADE certainty rated high. In adults the evidence is thin and mixed. A Morinaga-funded trial found BB536 lowered feverishness, while a trial of B. longum with L. helveticus found no effect on low mood. In preterm infants, B. longum from probiotic capsules has caused bloodstream infections.

Evidence grade: Limited evidence.

What goes wrong

Three extremely preterm infants given probiotics developed B. longum subsp. infantis bacteraemia; whole-genome sequencing showed their blood isolates matched the capsule strain. (Source 1)

• Case series, Low certainty.
• Size: 3 infants.
• Who: Extremely preterm infants on probiotic prophylaxis.
• How long: n/a.
• Result: Blood isolates identical to the probiotic strain.
• Funding: not stated.

showed that all 3 blood culture isolates and a B. longum strain cultured from an oral probiotic capsule were identical

The meta-analysis notes case reports of Bifidobacterium bacteraemia, but none of the included trials reported sepsis caused by the probiotic. (Source 2)

• Meta-analysis, Moderate certainty.
• Size: 67 RCTs.
• Who: Preterm infants.
• How long: n/a.
• Result: No probiotic-related sepsis in included RCTs.
• Funding: not stated.

Although there are few case reports of bacteraemia caused by the Bifidobacteria, it is reassuring to note that none of the RCTs included in our review that used probiotics reported probiotic related sepsis.

What the evidence supports

Across 67 trials in preterm infants (14,606 infants), probiotics containing B. infantis (16 trials) were linked to a larger drop in necrotising enterocolitis (RR 0.38) than probiotics without it (51 trials, RR 0.67); this is a between-trial subgroup comparison. (Source 3)

• Meta-analysis, High certainty.
• Size: 67 RCTs, 14,606 infants (16 RCTs with B. infantis)
• Who: Preterm and/or low-birth-weight infants.
• How long: Neonatal period.
• Result: NEC RR 0.38 (95% CI 0.27-0.55) with B. infantis vs 0.67 (0.55-0.81) without; subgroup p = 0.01.
• Funding: not stated on the fetched page.

The subgroup meta-analysis demonstrated greater reduction in the incidence of NEC in subgroup A than subgroup B

In 200 healthy adults, B. longum BB536 (1 x 10^10 CFU daily for 12 weeks) was linked to a lower incidence of self-reported feverishness in a diary compared with placebo, in a single industry-funded trial. (Source 4)

• Randomized trial, Low certainty.
• Size: 200 adults.
• Who: Healthy Japanese adults.
• How long: 12 weeks.
• Result: Significantly lower incidence of feverishness (effect size not given in the abstract)
• Funding: industry-funded (Morinaga Milk Industry)

Participants who consumed B. longum BB536 had a significantly lower incidence of feverishness, a systemic symptom, than the placebo group.

What the evidence does not support

A probiotic with L. helveticus and B. longum (products supplied by Lallemand) did not improve mood or any other psychological outcome in 79 adults with low mood; the authors call the result preliminary and say their sample may have been too severe or chronic to respond. (Source 5)

• Randomized trial, Low certainty.
• Size: 79 participants (10 dropouts)
• Who: Adults with at least moderate low mood, not on psychotropic medicines.
• How long: 8 weeks.
• Result: No significant difference on any psychological outcome (Cohen's d 0.07-0.16) or blood biomarker; MADRS responders 23% probiotic vs 26% placebo.
• Funding: industry-funded products (Lallemand Health Solutions)

No significant difference was found between the probiotic and placebo groups on any psychological outcome measure

Where the evidence is mixed

The meta-analysis authors call the B. infantis advantage indirect evidence that still needs confirming trials. (Source 3)

• Meta-analysis, Moderate certainty.
• Size: 67 RCTs.
• Who: Preterm infants.
• How long: n/a.
• Result: Subgroup comparison only.
• Funding: not stated.

These results provide indirect evidence that probiotic supplements that include B. infantis may be more beneficial for preterm infants.

How much

• Reference intake: No recommended intake or upper limit exists: live bacteria are not nutrients, and no body has set an RDA, AI or UL for them. No reference intake exists for Bifidobacterium longum. (Source 3)
• Upper limit: No tolerable upper intake level has been set for B. longum. (Source 3)
• Studied: B. longum BB536 powder, 1 x 10^10 CFU once daily for 12 weeks. (Source 4)
• Studied: L. helveticus plus B. longum preparation daily for 8 weeks. (Source 5)

A common belief, and what the research shows

The belief: Probiotic bifidobacteria are harmless for everyone, including premature babies.

What the research shows: Sequencing showed 'all 3 blood culture isolates and a B. longum strain cultured from an oral probiotic capsule were identical', although a meta-analysis found 'none of the RCTs included in our review that used probiotics reported probiotic related sepsis'.

Questions and answers

What is it?

B. longum is a gut bacterium, and its subspecies infantis specialises in eating human milk sugars. Different strains and subspecies are sold as probiotics. (Source 6)

What does it do in the body?

In babies, B. infantis digests human milk sugars and crowds out other gut bacteria such as Enterobacteriaceae. Probiotics containing it are linked to less necrotising enterocolitis in premature infants. (Source 6)

Is it good or bad for you?

The evidence is mostly favourable in preterm infants: the GRADE certainty for fewer cases of NEC was rated high. The same group of infants has also had bloodstream infections traced to the probiotic strain. In adults the benefits are unproven or mixed. (Source 7)

How do you get more of it?

In infants, human milk oligosaccharides feed B. infantis. Trials also gave B. longum as probiotic powders or capsules. (Source 6)

If it is harmful, what reduces it?

Does not apply in healthy people. In the preterm cases the organism was traced to the probiotic, so doctors stopped it and gave antibiotics. (Source 1)

Why might someone be low in it or missing it?

A large UK study found that caesarean birth, antibiotics given to the mother around delivery, and not breastfeeding all disrupt the gut bacteria babies acquire. That study reports the effect on Bacteroides and hospital pathogens, not on B. longum specifically. (Source 8)

Which whole foods contain it or feed it?

Human milk is the best-documented food that feeds B. infantis, through its oligosaccharides. We did not find strong evidence for particular adult whole foods. (Source 6)

What happens if you do not have it?

In premature infants, probiotic products containing B. infantis are linked to lower rates of NEC than products without it. Colonisation is also associated with better vaccine responses, but that finding is an association only. (Source 6)

How can you test for it?

Stool sequencing can detect bifidobacteria, but a NIST study found large disagreement between consumer testing companies analysing the same reference stool, put down to methods and weak quality control. (Source 9)

References

1. Emerging Infectious Diseases (CDC). Bifidobacterium longum Subspecies infantis Bacteremia in 3 Extremely Preterm Infants Receiving Probiotics. 2016. DOI 10.3201/eid2209.160033. Read the source
2. Pediatric Research. Bifidobacterium infantis as a probiotic in preterm infants: a systematic review and meta-analysis. 2023. DOI 10.1038/s41390-023-02716-w. Read the source
3. Pediatric Research. Bifidobacterium infantis as a probiotic in preterm infants: a systematic review and meta-analysis. 2023. DOI 10.1038/s41390-023-02716-w. Read the source
4. Journal of Functional Foods. Probiotic Bifidobacterium longum BB536 and its impact on subjective symptoms of physical conditions associated with common cold-like symptoms in healthy adults: A randomized, double-blind, placebo-controlled trial. 2024. DOI 10.1016/j.jff.2024.106113. Read the source
5. Australian & New Zealand Journal of Psychiatry. A double-blind, randomized, placebo-controlled trial of Lactobacillus helveticus and Bifidobacterium longum for the symptoms of depression. 2017. DOI 10.1177/0004867416686694. Read the source
6. Pediatric Research. Bifidobacterium longum subspecies infantis: champion colonizer of the infant gut. 2015. DOI 10.1038/pr.2014.156. Read the source
7. Pediatric Research. Bifidobacterium infantis as a probiotic in preterm infants: a systematic review and meta-analysis. 2023. DOI 10.1038/s41390-023-02716-w. Read the source
8. Nature. Stunted microbiota and opportunistic pathogen colonization in caesarean-section birth. 2019. DOI 10.1038/s41586-019-1560-1. Read the source
9. Communications Biology. Evaluating the analytical performance of direct-to-consumer gut microbiome testing services. 2026. DOI 10.1038/s42003-025-09301-3. Read the source