Lactobacillus casei Shirota (LcS) for Common Cold
Verdict: Published with Warning
Across 6 PubMed studies, the evidence for Lactobacillus casei Shirota (LcS) in Common Cold grades Tier B — preliminary evidence. Effective, but with safety or population caveats.
B 🟡 B Preliminary Evidence Published with Warning
Why this grade7-layer evidence engine
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Scoring transparency
All scores computed by a 7-layer evidence engine — fully auditableRaw score 0.62
D
C
B
A
S
← counter-evidence / ineffectiveeffective / strong evidence →
Final grade
B · Published with Warning
Confidence
59%
Conflicting evidence
Evidence level
E1
Cochrane high-quality SR/MA
▸View the full decision path (audit trail)
- compute_raw_score — 加權公式: L2×0.30 + L3×0.25 + L5×0.25 + L11×0.10 + L1×0.10 = 0.62
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 高品質 SR/MA 顯示 positive (2 篇 > 0 negative)
- tier_strict_requirement_check — Tier 條件達標，未降階
- detect_disputes — 偵測到 0 個 hard + 1 個 soft dispute
- decide_status — 依 tier + dispute 結果決定 status
PubMed studies (6)L2 · primary research & systematic reviews
Probiotics for preventing acute upper respiratory tract infections
Finding: Probiotics reduced the risk of having at least one acute URTI episode by ~24% (RR 0.76, 95% CI 0.67-0.87, P<0.001; 16 studies, 4798 participants), shortened mean episode duration (MD -1.22 days, 95% CI -2.12 to -0.33) and reduced antibiotic use (RR 0.58), but GRADE certainty was LOW.
View on PubMed Probiotics for Preventing Upper Respiratory Tract Infections in Adults: A Systematic Review and Meta-Analysis of Randomized Controlled Trials
Finding: Probiotics significantly reduced URTI incidence in adults (RR 0.77, 95% CI 0.68-0.87, P<0.0001, I2=26%) and shortened mean episode duration (MD -2.66 days, 95% CI -4.79 to -0.54, P=0.01), with the LcS Shirota trial among the included studies.
View on PubMed 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
Finding: URTI incidence was significantly lower with LcS fermented milk than control (22.4% vs 53.2%, P=0.002), with fewer cumulative episodes/symptom-days and shorter duration per episode; however blinding was not described and all authors are Yakult employees.
View on PubMed Lacticaseibacillus paracasei strain Shirota suppresses upper respiratory tract infections and activates mononuclear phagocytic cells in healthy Japanese office workers: a randomized, double-blind, controlled trial
Finding: LcS significantly lowered URTI incidence over the whole period (23.0% vs 33.3%, P=0.022; cumulative incidence P=0.016) and reduced symptom severity scores (20.3 vs 23.9, P=0.009), but the trial is small, short, and all authors are Yakult employees.
View on PubMed Efficacy of probiotics on digestive disorders and acute respiratory infections: a controlled clinical trial in young Vietnamese children
Finding: LcS fermented milk reduced ARI occurrence (15.9% vs 24.5%, OR 0.58, 95% CI 0.42-0.79, P<0.001) but had NO effect on ARI duration; it also cut constipation (OR 0.28). The trial was Yakult-funded and a large unblinded field trial.
View on PubMed Effects of Lactobacillus casei Shirota ingestion on common cold infection and herpes virus antibodies in endurance athletes: a placebo-controlled, randomized trial
Finding: LcS did NOT reduce common-cold episode incidence (mean 0.6/person, P=0.417), duration (5.6 vs 5.9 days, P=0.713) or severity versus placebo; it only lowered CMV/EBV antibody titres (surrogate immune markers, P<=0.003). Yakult-sponsored.
View on PubMed Regulatory & authoritative positionsL4/L5 · FDA / EMA / NIH ODS / Cochrane / Mayo …
L4a US FDA
Supportive
GRN No. 429 — Lactobacillus casei strain Shirota. Intended Use: As an ingredient in fermented dairy products at a maximum level of 4x10^8 colony forming units per milliliter. FDA Response: has no questions. Notifier: Yakult Honsha Co., Ltd. (Tokyo, Japan). Filed April 10, 2012; closed December 10, 2012. source↗
L4b EU EFSA
Against
The Panel concluded that a cause and effect relationship has not been established between the consumption of Lactobacillus casei Shirota and maintenance of the upper respiratory tract defence against pathogens by maintaining immune defences. The Panel considered that there was no human study demonstrating an effect of Lactobacillus casei Shirota consumption on upper respiratory tract infections… source↗
L4c UK NHS
Cautious
Probiotics are generally classed as food rather than medicine, which means they don't go through the rigorous testing medicines do. ... There's some evidence that probiotics may be helpful in some cases, such as helping to ease some symptoms of irritable bowel syndrome (IBS). ... If you have an existing health condition or a weakened immune system, you should talk to a doctor before taking any … source↗
L4d TW TFDA / 衛福部
Supportive
養樂多活菌發酵乳 衛署健食字第A00032號 胃腸功能改善；養樂多300LIGHT活菌發酵乳 衛署健食字第A00128號 免疫調節、輔助調整過敏體質、胃腸功能改善；養樂多300活菌發酵乳 衛署健食字第A00178號 胃腸功能改善 source↗
L4e WHO
Neutral
Probiotics are live microorganisms which when administered in adequate amounts confer a health benefit on the host. The 2002 FAO/WHO Working Group Guidelines for the Evaluation of Probiotics in Food require strain-level identification (genus, species, strain), in vitro testing (acid/bile tolerance), safety assessment (antibiotic resistance, metabolic activities, no transferable resistance), and… source↗
L5a NIH Office of Dietary Supplements
Neutral
With a total listing of over 500 scientific studies...it is fair to say that the L. casei strain Shirota is the most researched probiotic strain in the world. Classified as Lacticaseibacillus paracasei Shirota since April 2020. source↗
L5b Mayo Clinic
Supportive
Probiotics may be effective in preventing the common cold. Taking probiotics regularly can lower your chances of getting a cold. If you do catch a cold, probiotics may help reduce the severity of your symptoms and shorten how long they last. source↗
L5c Cleveland Clinic
Cautious
Some people take probiotics to improve their immunity during the cold and flu season. When taking probiotics preventively, like during cold and flu season, it might be harder to tell if they're working. You might notice you haven't been sick as often, but it's unclear whether that's due to the probiotics. source↗
L5d Harvard Health
Cautious
Looking the available data, there is weak evidence to support regular probiotics and zinc source↗
L5e Specialty Society (condition-mapped)
Cautious
Probiotics (any specified strain or dose) were better than placebo in reducing the number of participants experiencing episodes of acute upper respiratory tract infections... the quality of the evidence was low or very low. source↗