Serious vitamin D deficiency in healthcare workers during the COVID-19 pandemic.

Several reports suggest that vitamin D (VitD) deficiency could increase the predisposition to systemic infection, including respiratory tract infections and impaired immune response. A recent metaanalysis demonstrated that VitD supplementation can reduce the risk of respiratory tract infections overall based on data from randomised controlled trials. Moreover, an article reported a possible association of VitD level with cytokine storm and unregulated inflammation in elderly patients with COVID19. It supported the potential protective impact of VitD by enhancing the immune system and possibly reducing the risk of complications associated with cytokine storm and unregulated inflammation in patients with severe COVID19. VitD is a lipidsoluble vitamin that acts as a ligand to the intranuclear receptor superfamily and plays a significant role in regulating between innate and acquired immunity. 25Hydroxy vitamin D (25(OH)D) is the major circulating form of VitD in humans and currently accepted as the best marker of VitD status. To date, there are only a few reports focusing on nutritional status including 25(OH)D in healthcare workers (HCWs) during the COVID19 pandemic. During the COVID19 pandemic, we conducted a prospective observational study to evaluate several blood markers in HCWs at high risk of SARSCoV2 infection at the National Center for Child Health and Development in Tokyo, Japan. Blood sampling was performed from the enrolled participants from 1 March 2021 to 5 March 2021, and all clinical laboratory testing of the blood including VitD, zinc and natural killer (NK) cell activity were examined at the SRL Hachioji Laboratory Complex, in Tokyo, Japan. 25(OH)D was measured using chemiluminescent enzyme immunoassay, and serum zinc level was determined using the colorimetric method. Also, chromium51 release assay was used to assess the NK cell activity. We analysed the relationship between gender and VitD levels using the Fisher’s exact test. In addition, the correlationship between VitD levels and age was Letter