Abstract Background Heat-killed Lactobacillus helveticus MCC1848 is a postbiotic, which potentially aids in maintaining a positive mood. Daily intake of heat-killed L. helveticus MCC1848 for 4 weeks by healthy adults is known to be safe. However, the safety of long-term L. helveticus MCC1848 intake has not been investigated. Methods This study aimed to evaluate the safety of long-term intake of 25 billion heat-killed L. helveticus MCC1848 in healthy adults through a randomized controlled trial involving 40 participants. The study participants were randomly assigned to either the MCC1848 group ( n = 20) or placebo group ( n = 20). During a 12-week period, the MCC1848 group received the test powder containing 25 billion cells of heat-killed L. helveticus MCC1848, which is five times the minimum effective dose suggested for maintaining a positive mood. The placebo group received dextrin powder without any detectable heat-killed L. helveticus MCC1848. Safety evaluations included anthropometric and blood pressure measurements, hematological and biochemical tests, urinalysis, and adverse event monitoring. Results No clinical issues were observed in either of the biochemical evaluations. Furthermore, no adverse events were reported due to the intake of heat-killed L. helveticus MCC1848. Conclusions The results of this study suggest that 25 billion heat-killed L. helveticus MCC1848 for 12 weeks is safe for intake in healthy adults. Trial Registration The clinical trial was registered as UMIN000055233 (Registration Date: August 13, 2024) in the Clinical Trials Registry of the University Hospital Medical Information Network.
Aoki et al. (Tue,) studied this question.