GDF15 and COVID-19: GDF-15 increased the risk of severe COVID-19 in patients (OR = 1.10, 95% CI 1.03–1.19; P = .006); there was no causal effect of GDF-15 on hospitalization for COVID-19 (OR = 1.02, 95% CI 0.96–1.07; P = .47) or susceptibility to COVID-19 in the general population (OR = 1.010, 95% CI 0.988–1.034; P = .354).