SNK12 on Sleep Quality and Stress-Related Neuroendocrine and Inflammatory Biomarkers in Adults: A Randomized, Double-Blind, Placebo-Controlled, Parallel-Group Trial.

2025-12-24
Life (Basel, Switzerland) 16(1)
- Takumi Watanabe
- Shiho Kurosaka
- Yuriko Namatame
- Toshio Kawahara

PubMed: 41598182
DOI: 10.3390/life16010026

Heat-killed Lactiplantibacillus plantarum SNK12 (SNK), isolated from a traditional Japanese fermented food, has been suggested to influence sleep quality, but human data on sleep improvement with heat-killed lactic acid bacteria (postbiotics) remain limited. We conducted a randomized controlled trial to test whether heat-killed SNK (≥1 × 10¹¹ cells/day for 4 weeks) improves sleep quality and alters stress-related immune and neuroendocrine biomarkers. Healthy adults received SNK or a placebo for 4 weeks. The primary outcome was the Oguri-Shirakawa-Azumi Sleep Inventory MA version (OSA-MA) factor "Sleepiness on Rising"; secondary outcomes were other OSA-MA factors and the stress-related biomarkers salivary cortisol and plasma tumor necrosis factor-α (TNF-α). Compared with placebo, SNK improved Sleepiness on Rising (p = 0.032) and Initiation and Maintenance of Sleep (p = 0.010). Salivary cortisol (p = 0.016) and plasma TNF-α (p = 0.037) were also lower with SNK, and no safety concerns emerged. These concomitant changes in subjective sleep indices and stress-related biomarkers are consistent with modulation of hypothalamic-pituitary-adrenal axis activity and inflammatory pathways along the gut-brain axis. SNK may, therefore, represent a practical postbiotic option to support sleep quality.

Research Insights

Supplement	Health Outcome	Effect Type	Effect Size
Lactobacillus brevis SBC8803	Improved Sleep Quality	Beneficial	Small
Lactobacillus brevis SBC8803	Reduced Cortisol Levels	Beneficial	Small
Lactobacillus brevis SBC8803	Reduced Tumor Necrosis Factor Alpha	Beneficial	Small