Overcoming Infections Including COVID-19, by Maintaining Circulating 25(OH)D Concentrations Above 50 ng/mL

: The elderly and those with underlying chronic diseases (i.e., comorbidities) such as pulmonary, cardiovascular, metabolic, and renal diseases, increase their susceptibility to sepsis, including COVID-19. The SARS-CoV-2 virus damages pulmonary cells, causing acute respiratory distress syndrome (ARDS) and hypoxia. It further damages endothelial cells, altering clotting mechanisums causing intravascular hemolysis, microvascular thrombosis, and micro-embolization, contributing to the risk of death. Approximately 75% of the immune system functions of humans depend on vitamin D and the availability of sufficient amounts of vitamin D metabolites [vitamin D and 25(OH)D] concentrations to enter immune cells from the bloodstream. Such concentrations are achievable through sun exposure, targeted food fortification programs, and adequate daily or weekly vitamin D supplements. That would allow for generating 1,25(OH) 2 D (non-hormonal form of calcitriol) intracellularly in peripheral target cells like immune cells. This enables immune cells’ physiological functions, including intracrine/autocrine and paracrine signaling processes. This initiates and maintains robust immune functions, such as forming antibodies and antimicrobial peptides, suppressing inflammation, and increasing the expression of anti-inflammatory and antioxidant genes, thus, strengthening immune functions. The opposite occurs in hypovitaminosis D, increasing vulnerability to infections and dying from it. Therefore, governments should make the population sufficient with immunoceuticals—micronutrients, especially vitamin D, and other micronutrients: the most cost-effective intervention to keep the population healthy. The cost of such interventions are minuscule compared to the expenses related to increased hospitalizations and premature deaths. Supposed such a program was implemented in mid-2020 as the author proposed, we estimated that 50% of hospitalizations (and the associated healthcare costs) and a third of deaths from COVID could have been prevented. Described herein are cost-effective strategies using vitamin D to achieve and sustain serum D 3 and 25(OH)D concentrations crucial for maintaining a robust immune system, improving general health, minimizing disease severities and deaths, and reducing healthcare costs.