Objectives　This study aimed to evaluate the effect of onion extract containing concentrated cysteine sulfoxides on aging males’ symptoms（AMS）and testosterone levels using the randomized, double-blind, placebo-controlled, parallel-group comparative method.
Methods　Sixty healthy men（age 50-79 y）with mild or moderate AMS were randomly divided into test（n＝30）and placebo groups（n＝30）. Groups received onion extracts containing concentrated cysteine sulfoxides（30 mg）or placebo as three tablets daily for 4 weeks. Participants attended hospital three times during the study: day before the intake period（first visit）and 14th day（second visit）and 28th day（third visit）of the intake period. The AMS score, 36-item Short Form Survey（SF-36）, International Index of Erectile Function（IIEF）and biochemical parameters（serum total testosterone and salivary testosterone）were measured at each visit. Efficacy of the test food was determined by comparisons between the two groups at the second and third visits as well as comparisons between the first visit and the second or third visit in each group.
Results　All 60 participants completed the study, with no adverse events related to the onion extract. Twelve participants were excluded before efficacy analysis because of conflict with control criteria; the remaining 48 participants were analyzed. AMS scores（total score and mental subscale）of the test group were significantly lower than those of the placebo group at the third visit（total score: test group 29.0±1.1 vs. placebo group 32.4±1.2（P＝0.039）, mental subscale: test group 6.5±0.3 vs. placebo group 7.9±0.5（P＝0.027））. In the SF-36, mental health score of the test group was significantly higher than that of the placebo group at the third visit（test group 75.8±2.6 vs. placebo group 67.1±3.0（P＝0.035））. IIEF and serum and salivary testosterone levels did not differ significantly between test and placebo groups at the second or third visits. In the test group, salivary testosterone, which has been reported to be positively related to free testosterone in blood, was significantly higher at the second visit than the first visit but not at the third visit compared to the first visit. In the placebo group, salivary testosterone levels at the second and third visit did not differ from those at the first visit.
Conclusions　Onion extracts containing concentrated cysteine sulfoxides were shown to have an alleviating effect against AMS. Cysteine sulfoxides present in onions are suggested to be responsible for this activity.