Biomarkers with strong and consistent evidence include HO-1 activity, NOS-derived nitrate/nitrite levels, selenium deficiency, SOD2 rs4880 polymorphism, oxidative damage biomarkers such as MDA, 8-isoprostanes, nitrotyrosine, and miRNAs such as miR-21 and miR-146a, which reproducibly associate with oxidative stress regulation, severity, and immune dysregulation. The gene discussed is SOD2; the disease is selenium deficiency.