Effects of consuming S-allyl-L-cysteine enriched garlic extract on sleep quality in Japanese adults: A randomized, double-blind, placebo-controlled, parallel-group comparative study

Abstract

Introduction: Sleep promotes well-being, which includes physical and mental health, but many people suffer from sleep deprivation. One of the functional components of garlic, S-allyl-L-cysteine (SAC), can reportedly improve mental fatigue and is expected to regulate the autonomic nervous system and improve sleep quality. This study investigated the effects of SAC-enriched garlic extract intake on sleep quality in healthy Japanese adults.

Methods: This was a single center, stratified (male and female with balanced randomization [1:1]), double-blind, placebo-controlled, parallel-group study conducted from September 12, 2023, to February 25, 2024. Participants consumed either the SAC-enriched garlic extract tablet (2 mg/day as SAC) or placebo (22 participants per group) for 12 weeks. The assessment items included the Oguri-Shirakawa-Azumi sleep inventory middle-aged version (OSA-MA), the Japanese version of the Pittsburgh Sleep Quality Index (PSQI-J), and St. Mary’s Hospital sleep questionnaire (SMH). The primary outcome was the initiation and maintenance of sleep as measured by the OSA-MA after the 12-week intervention.

Results: The final analysis included 19 and 22 participants in the SAC and Placebo groups, respectively. An additional subgroup analysis explored the effect of SAC intake on sleep quality, with 14 and 19 participants in the SAC and Placebo groups, respectively. After the 12-week intervention, the overall analysis showed no significant differences between groups for the primary outcome. In the subgroup analysis, however, the “Initiation and maintenance of sleep” and “Sleepiness on rising” scores in the OSA-MA significantly increased in the SAC group versus placebo. Both the overall and subgroup analyses revealed a decreased total score, subjective sleep quality (C1), and sleep latency (C2) of PSQI-J in the SAC group versus placebo. Regarding the question “How much difficulty did you have in falling asleep last night?” in the SMH, more participants in the SAC group reported “none or very little” in the overall analysis, while all participants reported “none or very little” in the subgroup analysis after the intervention.

Conclusions: SAC-enriched garlic extract relieves difficulties associated with initiating and maintaining sleep.

Keywords: garlic, S-Allyl-L-Cysteine, sleep quality, falling asleep, sleep maintenance

Trial registration number: UMIN000052187