Lactobacillus casei Shirota
What it is
The probiotic strain in Yakult, with a long history of human studies spanning decades (the "100+ trials" figure is company-reported and includes non-RCT work). Multiple trials show reductions in upper respiratory infection duration, improved gut transit time, and reduced stress-related digestive symptoms. Takada 2016 and Kato-Kataoka 2016 in students reported improvements in stress and cortisol markers, though mood/anxiety evidence in broader populations is more limited. Very safe with one of the longest track records of any probiotic strain.
Dose
6.5–40 billion CFU/day; the original Yakult strain with 100+ human trials
Time of day & tips
Take daily at the same time, ideally with a small meal. Refrigerate. Results for stress and immunity build over several weeks of consistent use.
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