Cobalt has also been used as a treatment for anemia, because it stimulates red blood cell production. Other effects noted in humans from inhalation exposure to cobalt include cardiac effects, such as functional effects on the ventricles and enlargement of the heart, congestion of the liver, kidneys, and conjunctiva, and immunological effects that include cobalt sensitization, which can precipitate an asthmatic attack in sensitized individuals. The effects were characterized by cardiogenic shock, sinus tachycardia, left ventricular failure, and enlarged hearts. In one oral study, no developmental effects on human fetuses were observed following treatment of pregnant women with cobalt chloride. These effects on the offspring occurred at levels that also caused maternal toxicity.
Limited data are available on the carcinogenic effects of cobalt.
In one study on workers that refined and processed cobalt and sodium, an increase in deaths due to lung cancer was found for workers exposed only to cobalt. However, when this study was controlled for date of birth, age at death, and smoking habits, the difference in deaths due to lung cancer was found to not be statistically significant. In another study assessing the correlation between cancer deaths and trace metals in water supplies in the United States, no correlation was found between cancer mortality and the level of cobalt in the water. In an animal study, inhalation of cobalt over a lifetime did not increase the incidence of tumors in hamsters. Cobalt, via direct injection under the muscles or skin, has been reported to cause tumors at the injection site in animals.