IGF1 and COVID-19: Testosterone is converted to estradiol by aromatase and has a stimulatory effect on the growth hormone axis.19,20 There is a decline in estradiol and insulinlike growth factor (IGF-1) concentrations in men and women with age, and lower IGF-1 concentrations have been associated with acute respiratory distress syndrome.21 In contrast, higher estradiol concentrations during hospitalization are associated with increased mortality in both sexes.22 It is not known whether estradiol and IGF-1 concentrations are associated with disease severity in individuals with COVID-19.