In this randomized controlled trial in healthy adults, we evaluated whether ingestion of heat-killed SNK at a dose of ≥1 × 1011 cells/day for 4 weeks improves subjective sleep indices (Oguri–Shirakawa–Azumi Sleep Inventory MA version [OSA-MA]) and stress-related neuroendocrine and inflammatory biomarkers (salivary cortisol, plasma TNF-α). Here, TNF is linked to obstructive sleep apnea syndrome.