Microbiome Modulator

Lactobacillus Casei

Lacticaseibacillus casei

Evidence TierCWADA NOT PROHIBITED

tuneTypical Dose

10000000000-100000000000

watchEffect Window

Usually assessed over 8-12 weeks.

check_circleCompliance

WADA NOT PROHIBITED

Overview

Clinical Summary

Lactobacillus casei is a strain-dependent probiotic, and current pooled evidence does not support broad IBS claims for L. casei Shirota.

The better-supported evidence for L. casei remains narrow and strain specific. A newer strain-specific IBS meta-analysis did not show pooled benefit for L. casei Shirota, so digestive claims need to stay restrained. Limited immune-support signals exist in selected URTI studies, but they should not be generalized broadly.

Strain-specific probiotic effects on mucosal immunity and gut-lung immune signaling with mixed clinical translation.

Outcomes

What This Is Expected To Influence

Primary Outcomes

  • Upper respiratory infection incidence and duration (population-dependent)
  • IBS symptom burden (inconsistent, often null short-term)

Secondary Outcomes

  • Immune biomarkers (NK activity, viral antibody titers)
  • Stress-linked immune measures (salivary cortisol in limited data)

Safety

Contraindications and Interactions

Contraindications

  • Severe immunosuppression without clinician supervision
  • Critical illness/ICU status
  • Central venous catheter dependence

Side effects

  • Bloating
  • Gas
  • Mild abdominal discomfort

Interactions

  • Antibiotics can reduce viable probiotic exposure
  • Multi-strain combinations may not replicate monostrain trial results
  • High prebiotic doses may increase transient GI side effects

Avoid if

  • Neutropenia or severe immune compromise
  • Active sepsis
  • High endocarditis-risk setting without specialist input

Evidence

Study-level References

lactobacillus-casei-SRC-001Randomized controlled trial
Sourceopen_in_new

Shida K, et al. Daily intake of fermented milk with Lactobacillus casei strain Shirota reduces the incidence and duration of upper respiratory tract infections in healthy middle-aged office workers. Eur J Nutr. 2017;56(1):45-53. doi:10.1007/s00394-015-1056-1. PMID:26419583

Population: 96 healthy male office workers, winter season

Dose protocol: LcS-fermented milk, 1.0 × 10^11 CFU/day, 12 weeks

Key findings: URTI incidence and duration improved versus control

Notes: Single demographic and industry-affiliated program context

Paper content

URTI incidence and duration improved versus control

lactobacillus-casei-SRC-002Strain-specific systematic review with meta-analysis of randomized placebo-controlled trials
Sourceopen_in_new

Maslennikov R, Gosteeva E, Ananeva V, et al. Strain-Specific Systematic Review with Meta-Analysis of Probiotics Efficacy in the Treatment of Irritable Bowel Syndrome. J Clin Med. 2026;15(3):1152. doi:10.3390/jcm15031152. PMID:41682832.

Population: Patients with irritable bowel syndrome across 32 articles evaluating 10 single-strain probiotics.

Dose protocol: Strain-specific IBS meta-analysis of randomized placebo-controlled single-strain probiotic trials

Key findings: Did not demonstrate efficacy for Lactobacillus casei Shirota in IBS.

Notes: Stronger signal than one trial alone because it pools strain-specific IBS evidence.

Paper content

This 2026 strain-specific meta-analysis is useful because it directly tests the probiotic overgeneralization problem. When IBS data were pooled by strain, Lactobacillus casei Shirota did not demonstrate efficacy, while several other strains did. That makes it hard to justify species-level digestive claims for L. casei without naming a strain and target endpoint.

lactobacillus-casei-SRC-003Randomized, double-blind, placebo-controlled trial
Sourceopen_in_new

Gleeson M, et al. Effects of Lactobacillus casei Shirota ingestion on common cold infection and herpes virus antibodies in endurance athletes: a placebo-controlled, randomized trial. Eur J Appl Physiol. 2016;116(8):1555-1563. doi:10.1007/s00421-016-3415-x. PMID:27294502

Population: 243 university endurance athletes/games players

Dose protocol: Daily probiotic vs placebo for 20 weeks

Key findings: No URS clinical benefit. Antibody titers improved in seropositive subgroup

Notes: Unexpectedly low URS incidence limits clinical endpoint power

Paper content

No URS clinical benefit; antibody titers improved in seropositive subgroup

lactobacillus-casei-SRC-004Narrative review
Sourceopen_in_new

Kullar R, et al. Lactobacillus Bacteremia and Probiotics: A Review. Microorganisms. 2023;11(4):896. doi:10.3390/microorganisms11040896. PMID:37110319

Population: Lactobacillus bacteremia literature with probiotic linkage analysis

Dose protocol: Not a dosing trial

Key findings: Rare but clinically important invasive infection risk in high-risk patients

Notes: Narrative design and author conflicts disclosed

Paper content

Rare but clinically important invasive infection risk in high-risk patients

lactobacillus-casei-SRC-005Systematic review and network meta-analysis of randomized controlled trials.
Sourceopen_in_new

Rokkas T, Ekmektzoglou K, Tsanou E, et al. Comparative effectiveness and safety of probiotics with psychotropic potential in mental health benefits in irritable bowel syndrome: a systematic review and network meta-analysis. Eur J Gastroenterol Hepatol. 2026;38(1):27-35. doi:10.1097/MEG.0000000000003062. PMID:40929652.

Population: Adults with irritable bowel syndrome assessed for mental health outcomes.

Dose protocol: Network meta-analysis comparing nine probiotic interventions for IBS-related mental health outcomes

Key findings: L. casei Shirota was not among the top-ranked strains for anxiety or depression in IBS. B. longum and probiotic combinations ranked higher.

Notes: Reinforces the limited IBS efficacy profile for L. casei Shirota across multiple outcome domains.

Paper content

This network meta-analysis compared nine probiotic interventions for mental health outcomes in IBS patients. B. longum and multi-strain combinations emerged as the most effective treatments versus placebo for anxiety and depression in IBS. L. casei Shirota was included in the comparative analysis but was not highlighted among the top performers. This adds to the pattern of L. casei Shirota showing limited benefit for IBS outcomes, consistent with earlier strain-specific meta-analyses that found no pooled IBS efficacy for this strain. The study is relevant because it places L. casei Shirota in a competitive landscape alongside other probiotics, reinforcing that strain selection matters for IBS-related endpoints.

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