This randomized, double-blinded, placebo-controlled and crossover study examined the effects of an onion extract containing concentrated cysteine sulfoxides (at least 6%) on sleep quality. 30 healthy adults have been enrolled and received a placebo or the extract (1500 mg, providing isoalliin (13 mg), methyiin (3 mg), and cycloalliin (17 mg)) for 5 days. Participants at a score greater than 6 on the Pittsburg Sleep Quality Index, and were considered to be dissatisfied with their sleep.

The delta power during non-rapid eye movement sleep and the delta power per minute in the first sleep cycle increased significantly with the intake of onion extract in comparison to placebo. Moreover, a decrease in sleep latency has also been measured, as a decrease in salivary alpha-amylase level.

Therefore, the tested onion extract was effective for improving sleep quality in healthy adults, even if larger studies are warranted to confirm these first results.

Nakayama Y, Makita M, Nozaki S, Kikuchi Y. Effects of onion extract containing concentrated cysteine sulfoxides on sleep quality: a randomized, double-blind, placebo-controlled, crossover study. Food Sci Biotechnol. 2020 Oct 6;29(12):1755-1762.

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