Effects of onion extract containing concentrated cysteine sulfoxides on sleep quality: a randomized, double-blind, place
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Effects of onion extract containing concentrated cysteine sulfoxides on sleep quality: a randomized, double-blind, placebocontrolled, crossover study Yuya Nakayama1
•
Miki Makita2 • Satomi Nozaki1 • Yosuke Kikuchi1
Received: 24 March 2020 / Revised: 1 September 2020 / Accepted: 15 September 2020 Ó The Korean Society of Food Science and Technology 2020
Abstract The objective of this randomized, double-blind, placebo-controlled, crossover study was to examine the effects of onion extract containing concentrated cysteine sulfoxides on improving sleep quality. In total, 30 healthy men and women who were dissatisfied with their sleep consumed the test food sample (onion extract tablets) for 5 days. 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 containing concentrated cysteine sulfoxides compared with the intake of placebo. A significant decline in sleep latency was also observed. Salivary a-amylase level, a stress indicator, decreased significantly with the intake of onion extract containing concentrated cysteine sulfoxides compared with the intake of placebo. These findings indicate that onion extract containing concentrated cysteine sulfoxides alleviates stress, improves the quality of sleep and promotes smooth transition into sleep. Keywords Onion Cysteine sulfoxide Non-rapid eye movement sleep Delta power Sleep quality
& Yuya Nakayama [email protected] 1
Research Center for Basic Science, Research and Development, Quality Assurance Division, Nisshin Seifun Group Inc., Saitama 356-8511, Japan
2
Health Care Research Center, Nisshin Pharma Inc., Saitama 356-8511, Japan
Introduction Sleep in humans consists of non-rapid eye movement (NREM) sleep and rapid-eye movement (REM) sleep. NREM sleep, which is a stage of deep sleep, is responsible for numerous physiological functions such as consolidation of memory (Born and Wilhelm, 2012), cognitive performance while awake (Ferrara et al., 2000) and glycemic control (Spiegel et al., 2009). Research has shown that when sleep quality declines with light sleep, it increases the risk for developing diseases such as diabetes (Tasali et al., 2008). Therefore, it is essential to maintain and improve the quality of sleep. Improvement in the quality of sleep is assessed by the depth of NREM sleep due to the increased delta power (Monoi et al., 2016). Poor sleep quality is thought to be caused by various stressors (Fruhstorfer et al., 1984; Pasternak et al., 1992). Increased psychological stress and lack of ability to adequately cope with stress have been reported to increase the risk of insomnia (Kim et al., 2000). This means that alleviating stress is extremely important for improving sleep quality. Onion contains about 0.2% (dry matter conversion) cysteine sulfoxides (isoalliin, methyiin, and cycloalliin) as characteristic amino acids, which brings about the pungent aroma and taste of onions (Kim et al., 2016). Cysteine sulfoxides are cleaved
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