SARS-CoV-2, the cause of COVID-19, has led to more than 338 million cases and over 5.71 million deaths worldwide as for February 4, 2022. Mexico is one of the most affected countries, with more than 5.03 million infections and more than 307,000 deaths (1). COVID-19 pandemic coexists with vitamin D (VD) deficiency, which is also a major public health problem, both globally (, , ) and in Mexico (5). This is relevant because of the well-known immunomodulatory role of VD as it attenuates Th1 cell and stimulates Th2 cell proliferation, favoring the synthesis and secretion of anti-inflammatory cytokines, and limiting the production of pro-inflammatory mediators (6). Therefore, it is expected that VD deficiency increases the susceptibility to bacterial and viral infections, including SARS-CoV-2.
Very active research regarding VD and COVID-19 has been conducted in the last two years. Cross sectional, as well as large population-based studies have found an inverse correlation between serum 25-hydroxyvitamin D3 concentrations and SARS-Cov-2 positivity rate, severity, and mortality (, , , , , ). Furthermore, meta-analyses of case-control and cohort studies conclude that individuals with lower 25-hydroxyvitamin D3 concentrations not only have an increased risk of SARS-CoV-2 positivity but are also more likely to require admission to intensive care units and to dye from the disease. However, most of these meta-analyses report a high degree of heterogeneity, and low precision or certainty of the analyzed studies (, , ).
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