Combined NY1301 and DDMP on Sleep and Autonomic Function in Summer: A Randomized Clinical Trial

Objectives: Summer heat can impair sleep and contribute to autonomic dysregulation and fatigue-related symptoms. Because heat exposure may induce oxidative stress and gut-related dysfunction, we hypothesized that combined intake of the probiotic Lacticaseibacillus paracasei subsp. paracasei NY1301 and the antioxidant 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one (DDMP) would improve sleep, fatigue, and autonomic recovery during the summer. Methods: In this randomized, double-blind, placebo-controlled, parallel-group trial, 171 healthy adults were administered a beverage containing NY1301 and DDMP or placebo once daily for 8 weeks during the summer. The primary outcome was subjective fatigue assessed by a web-based daily log. Secondary outcomes included visual analog scale (VAS) fatigue scores, weekly questionnaire items, sleep parameters, and heart rate variability before and after mental arithmetic tasks. Results: No statistically significant between-group difference was observed in the primary outcome, subjective fatigue assessed using the web-based daily log. However, among secondary outcomes, sleep onset latency at week 8 was significantly shorter in the NY1301 + DDMP group (mean difference: −2.07 min, 95% CI −3.96 to −0.17; p = 0.033), and pre-task fatigue VAS at week 8 was lower (mean difference: −6.79, 95% CI −13.6 to −0.3; p = 0.047). At week 8, the NY1301 + DDMP group showed a greater increase in LF/HF during the task (mean difference: 1.32, 95% CI 0.06 to 2.58; p = 0.040), greater decrease in LF/HF during recovery (mean difference: −1.34, 95% CI −2.39 to −0.30; p = 0.012), and greater increase in HF during recovery (mean difference: 140, 95% CI 43 to 239; p = 0.005). In an exploratory analysis, the temperature-associated rise in nocturnal respiratory rate was significantly attenuated in the NY1301 + DDMP group (group × temperature interaction, p < 0.05). Conclusions: The primary outcome, subjective fatigue assessed using the web-based daily log, was not significantly different between groups during the summer study period. However, combined intake of NY1301 and DDMP was associated with shorter sleep onset latency, lower pre-task fatigue under standardized conditions, attenuation of the temperature-associated rise in nocturnal respiratory rate, and more pronounced post-stress autonomic recovery during the summer. These findings suggest a potential physiological benefit of this combined nutritional approach under summer conditions and warrant confirmation in independent trials. The study was funded by Nissin York Co., Ltd., and potential conflicts of interest related to sponsor-affiliated authors are disclosed in the manuscript.