Benefits
Days with self-rated upper respiratory and fatigue symptoms in healthy adults
In 192 analyzed healthy adults, 6 billion heat-killed cells a day for 8 weeks gave 938 symptom days versus 1116 on placebo for the main outcome, about 9.8 versus 11.6 days per person. Days were pooled and tested as independent, not per person, a weak analysis. Chills days were higher with the strain. The maker ran the trial.
Symptom days at a lower and a higher daily dose
In a second maker-run trial, 6 billion or 100 billion heat-killed cells a day for 8 weeks were compared with placebo, with a cold-like symptom questionnaire as the main outcome. Both doses had fewer days with several symptoms by a chi-square test on cumulative days; the high dose did not lower runny nose, nasal congestion or sneezing days. Participant numbers were not stated in what was read.
Activation markers on blood dendritic cells
In a subgroup of the first trial, the change in the activation marker HLA-DR on plasmacytoid dendritic cells was larger than with placebo at 4 and 8 weeks, and HLA-DR on type 1 conventional dendritic cells was higher than placebo at 8 weeks, although its change from baseline only trended higher (p = 0.074). Markers on type 2 dendritic cells did not differ. A blood marker is not the same as fewer illnesses.
Saliva IgA antibody secretion
The second trial reported a higher saliva IgA secretion rate with the strain after 8 weeks at both doses. In the first trial, which used 6 billion cells a day, saliva IgA concentration and secretion rate did not differ from placebo at 4 or 8 weeks. The two maker-run trials therefore disagree on this marker.
Natural killer cell activity and blood cytokines
In the first trial, natural killer cell activity, activation of T cells, B cells and natural killer cells, and blood interferons, IL-6, TNF-alpha and IL-12 did not differ from placebo at 4 or 8 weeks; IL-12p40 showed only a trend at 8 weeks (p = 0.080).
Immune cell responses to the strain (lab work)
In the maker's laboratory tests with human cells, heat-killed GCL1815 raised IgA production, a dendritic cell activation marker and IL-12 more than most of 308 strains screened, and activated dendritic cells increased T cell growth and interferon-gamma. These are test-tube results and are not outcomes in people.
Mechanism of action
Dendritic cell activation (lab work)
In human monocyte-derived dendritic cells, heat-killed GCL1815 raised HLA-DR and CD86 and strongly increased IL-12p70; these cells then increased CD4 and CD8 T cell growth and interferon-gamma output in co-culture, a pattern called a Th1-skewed response. All of this work comes from the maker's laboratory.
Cell wall recognition through TLR2 (proposed)
In a human monocyte cell line, blocking the TLR2 receptor partly reduced IL-12p40 output in response to the strain, while blocking TLR4 had no effect. The authors propose that cell wall components recognized by TLR2 explain part of the activity, which would not need living cells.
Heat-killed cells as a postbiotic
Because the cells are heat-sterilized, any effect would come from bacterial structures rather than growth in the gut. An international expert panel defines such preparations of inanimate microbes that confer a health benefit as postbiotics; that definition does not itself show a benefit for this strain.
Clinical trials
Randomized, double-blind, placebo-controlled parallel trial at a Tokyo clinic (January to March 2023) of one capsule a day with 6 billion heat-sterilized GCL1815 cells or a placebo capsule for 8 weeks; the primary endpoint was a daily 14-item cold-symptom diary, analyzed as cumulative symptom days pooled across participants (person-days) with a chi-squared test rather than per person; registered UMIN000049616 (funding source listed as Ezaki Glico) and UMIN000053740 for the additional analysis; the paper states no external funding (Wada et al. 2024, Nutrients)
200 healthy Japanese adults aged 20 to 64 with at least one cold symptom in the previous year; 192 in the per-protocol efficacy analysis (96 per group) and 80 in an immune-marker subgroup.
Cumulative days with cold-like symptoms were 938 with GCL1815 versus 1116 with placebo out of 5,376 person-days per group (p < 0.001, chi-squared on person-days), about 9.8 versus 11.6 days per person; no per-person analysis was reported. Feverishness, fatigue, tiredness, runny nose, nasal congestion and phlegm days were lower, chills days were higher with GCL1815 (95 versus 51), and 7 other symptoms did not differ. HLA-DR change on plasmacytoid dendritic cells was greater than placebo at 4 and 8 weeks; NK cell activity, saliva IgA and cytokines did not differ. 37 adverse events in 23 of 200 people, none judged related. Four of the five authors are Ezaki Glico employees.
Randomized, double-blind, placebo-controlled parallel-group trial of 6 billion (low dose) or 100 billion (high dose) heat-sterilized GCL1815 cells a day versus placebo for 8 weeks; the primary endpoint was a cold-like symptom questionnaire, and the maker's summary reports symptom days compared with a chi-squared test; not indexed in PubMed, and only the abstract and the maker's summary were read (Kikuchi et al. 2025, J Funct Foods)
Healthy Japanese adults; the number enrolled was not stated in the abstract or the maker's summary that were read.
Both doses had significantly fewer days with several individual systemic and local cold-like symptoms than placebo after 8 weeks; the maker lists 13 improved symptoms for the low dose and 10 for the high dose, with runny nose, nasal congestion and sneezing not among those listed for the high dose. Saliva IgA secretion rate was higher than placebo at 8 weeks in both dose groups. No safety concerns were reported, including at 100 billion cells a day. Eight of the nine authors are listed with Ezaki Glico affiliations in the bibliographic record.