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. 2024 Feb;18(1):33-45.
doi: 10.4162/nrp.2024.18.1.33. Epub 2024 Jan 11.

Effect of onion (Allium cepa L.) peel extract on natural killer cell and cytokines in a randomized, double-blind, placebo-controlled trial

Hyunji Cho  1 , Sohui Kim  1 , Sung Hyen Lee  2 , Yongsoon Park  1
Affiliations

Effect of onion (Allium cepa L.) peel extract on natural killer cell and cytokines in a randomized, double-blind, placebo-controlled trial

Hyunji Cho et al. Nutr Res Pract. 2024 Feb.

Abstract

Background/objectives: Onion, particularly onion peel, is a quercetin-rich food with, anti-inflammatory and immunomodulatory effects. However, the effect of onion peel extract (OPE) in humans is unclear. Thus, the present study aimed to investigate whether OPE improves natural killer (NK) cell activity and cytokine concentration in a randomized double-blind placebo-controlled trial.

Subjects/methods: Eighty participants aged 19-64 yrs old with a white blood cell count of 4,000-10,000 cells/µL, symptoms of upper respiratory infection at least once within the previous 12 mon, and perceived stress scale (PSS) over 14 were included. Participants were randomly assigned to take either 1,000 mg/day OPE or a placebo for 8 weeks.

Results: Compliance were 87.4 ± 8.6% and 86.9 ± 79.0% in OPE and placebo groups. Compared to the placebo, OPE supplementation improved "Hoarseness" (P = 0.038) of the Wisconsin Upper Respiratory Symptom Survey (WURSS)-21 symptom, and stress scores (P = 0.001; 0.021) of PSS. Supplementation of OPE had no significant effect on NK cell activity and concentrations of cytokines such as interleukin (IL)-2, IL-6, IL-12, IL-1β, interferon-γ, and tumor necrosis factor-α. At baseline, the WURSS-21 symptom and PSS score (P = 0.024; 0.026) were higher in the OPE group than the placebo group. Among participants with higher than median WURSS-21 symptom score, OPE supplementation increased NK cell activity (P = 0.038). Supplementation of OPE had no significant effects on safety measurements and adverse events.

Conclusions: The present study suggested that OPE supplementation improves NK cell activity in participants with moderate upper respiratory symptoms without any significant adverse effects.

Trial registration: ClinicalTrials.gov Identifier: NCT05666752.

Keywords: Cytokine; natural killer cells; onion; perceived stress scale; respiratory symptom.

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Conflict of interest statement

Conflict of Interest: The authors declare no potential conflicts of interests.

Figures

Fig. 1
Fig. 1. Schematic diagram of the study design.
NK, natural killer; OPE, onion peel extract.
Fig. 2
Fig. 2. NK cell activity according to the WURSS-21 symptom score between OPE and placebo for 8 weeks. P-values were determined by the independent t-test or χ2 test between OPE and placebo groups.
NK, natural killer; OPE, onion peel extract; WURSS-21, Wisconsin Upper Respiratory Symptom Survey-21.
See this image and copyright information in PMC

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