Effect of Welsh onion (Allium fistulosum L.) green leaf extract on immune response in healthy subjects: a randomized, double-blind, placebo-controlled study

Background: Welsh onion belongs to genus allium. Although its medicinal benefit such as cold prevention is well known by tradition, the underlying mechanism and active components have never been elucidated. The recent study revealed that Welsh onion mucus enhances tumor necrosis factor-α and monocyte chemotactic protein-1 production from RAW 264 cells and natural killer (NK) cell activity in murine spleen cells. This mucilage was abundant in the leaf blade of Welsh onion. Thus, we investigated the effect of Welsh onion green leaf extract (GLE) on immune competence in the human clinical trial. Methods: A randomized, double-blind, placebo-controlled trial was conducted. Fifty-five healthy subjects were enrolled after the screening based on NK cell activity, and each sample (placebo, low-dose GLE or high-dose GLE) was supplemented for four weeks. The immune competence activity was evaluated through the primary endpoints that were NK cell activity and the score of immunological vigor (SIV). The SIV was calculated from lymphocyte subset analysis by flow cytometry method.Results: NK cell activity was enhanced in all supplemented groups including placebo, especially, it was significant in both GLE groups. The result of immune score showed that the immunity of high-dose GLE group did not change although it was significantly lowered in placebo group (p