EPO and polycythemia: It can stimulate erythropoietin (EPO) synthesis in the kidneys by activating HIF pathways, leading to increased red blood cell production.[190] Historically, cobalt salts were used to treat certain types of anemia before the advent of recombinant EPO therapy.[191] However, excessive cobalt intake can lead to polycythemia, which is characterized by an abnormally high concentration of red blood cells, increasing blood viscosity, and the risk of thrombosis.[192]