Review Article 綜合論述
Coronavirus disease 2019 (COVID-19) pandemic has been a global challenge with high morbidity and mortality. The viruses enter the host cells via angiotensin converting enzyme 2 (ACE2) receptors which are abundantly present in humans. The incurred ACE/ACE2 imbalance and a serial immuno-inflammatory dysregulation are responsible for the extended injury.
The major biological functions of vitamin D against COVID-19 and its complications involve the antiviral activity with β-defensin 2 and cathelicidin LL-37, regulation of ACE/ACE2 balance, suppression of cytokine storm and oxidative stress, alleviation of gut dysbiosis and gut leakage, production of endothelial nitric oxide synthetase (eNOS) to ameliorate cerebrovascular function and prevent platelet aggregation. The efficacy and safety of vitamin D, an inactive hormone per se, depend on the concentration of its active metabolites, such as 25(OH)D (calcidiol) and 1α, 25(OH)2D (calcitriol), which directly regulate up to 3 000 human genes. The serum 25(OH)D is defined as the biomarker of vitamin D status, and its level below 200 ng/mL is believed to be safe.
Vitamin D deficiency is highly prevalent in COVID-19 cases and inversely associated with the mortality odds. Clinical studies suggest “optimal” vitamin D therapy with “early” and “adequate” supplementation improves outcome of COVID-19. The regimen of daily 70 000 IU of vitamin D for 7 days may be recommended to rapidly correct its deficiency, raise serum 25(OH)D level over 60 ng/mL and also prevent hypercalcemia. A maintenance dose is required to stay at the therapeutic level with daily or weekly 70 000 IU depending on the vitamin D status on day 8.