Does atmospheric dimethyldiselenide play a role in reducing COVID-19 mortality?

Environmental selenium (Se) distribution in the US is uneven, yet US residents appear to have a relatively narrow range of serum Se concentrations, according to the NHANES III survey data; this is probably due to the modern food-distribution system. In the US, Se concentration in alfalfa leaves has been used as a proxy for regional Se exposure (low, medium or high, corresponding to ≤ 0.05, 0.06-0.10 and ≥ 0.11 ppm respectively). Se in plants, soil, water, and bacteria can be transformed into volatile dimethyldiselenide, which can be inhaled and excreted via the lung. Hence, pulmonary Se exposure may be different in states with different atmospheric Se levels. We found a significantly higher death rate from COVID-19 in low-Se states than in medium-Se or high-Se states, though the case densities of these states were not significantly different. Because inhaled dimethyldiselenide is a potent inducer of nuclear-factor erythroid 2 p45-related factor 2 (Nrf2), exposure to higher atmospheric dimethyldiselenide may increase Nrf2-dependent antioxidant defences, reducing the activation of NFκB by SARS-CoV-2 in the lung, thereby decreasing cytokine activation and COVID-19 severity. Atmospheric dimethyldiselenide may thereby play a role in COVID-19 mortality, although the extent of its involvement is unclear.