Severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) gains access to host cells by attaching to angiotensin‐converting enzyme 2 (ACE2). Vitamin D (VitD) can upregulate ACE2 and has an antagonistic effect on Renin, which exerts a vasodilatation and anti‐inflammatory effect against coronavirus disease (COVID‐19). However, it may also facilitate viral entry by increasing ACE2 as the main SARS‐CoV‐2 receptor and mediates ROS production through NADPH oxidase, as a double‐edged sword effect. Lung function and the immune system are also influenced by VitD through several mechanisms, including increased natural antibiotics (Defensin and Cathelicidin) and upregulated transforming growth factor‐β. A higher IgA, Th2/Th1 ratio, and T‐regulatory cells are attributable to VitD effects on the immune cells, while these changes may also be a double‐edged sword in COVID‐19. Although VitD supplementation might be highly recommended in COVID‐19, the administration's dosage and route could be challenging. Furthermore, this issue has not been mentioned in various studies so far. So, the report aimed to explain the current challenges with the application of VitD in COVID‐19.

中文翻译：

---

维生素D对COVID-19可能产生的双刃剑效应：一个假设

严重急性呼吸系统综合症冠状病毒2（SARS-CoV-2）通过与血管紧张素转化酶2（ACE2）结合而进入宿主细胞。维生素D（VitD）可以上调ACE2并对肾素产生拮抗作用，从而对冠状病毒疾病（COVID-19）发挥血管舒张作用和抗炎作用。但是，它也可以通过增加作为主要SARS-CoV-2受体的ACE2来促进病毒进入，并通过NADPH氧化酶介导ROS的产生，这是双刃剑的作用。VitD还通过多种机制影响肺功能和免疫系统，包括增加天然抗生素（防御素和Cathelicidin）和上调转化生长因子-β。更高的IgA，Th2 / Th1比值和T调节细胞归因于VitD对免疫细胞的影响，而这些更改在COVID-19中也可能是一把双刃剑。尽管在COVID-19中可能强烈建议补充VitD，但给药的剂量和途径可能具有挑战性。此外，迄今为止，在各种研究中都未提及该问题。因此，该报告旨在解释VitD在COVID-19中的应用当前面临的挑战。