Depending on local soil conditions, the dietary intake of the essential trace element selenium can vary greatly. Geographical, geological and geochemical factors often lead to a clinically relevant deficiency in selenium. In many countries like Germany where soil is selenium-poor, individuals commonly suffer from too low selenium levels. These individuals are at risk of adverse effects to health. Selenium deficiency may also be a sign of other clinical disorders, can make certain viruses more virulent, is associated with weakened immunity, cardiomyopathy, thyroid problems and even reduced sperm production. To help, lab workups can determine a person’s selenium status and whether selenium supplementation is required. This would be the case if levels are < 80 μg/L in the serum or < 100 μg/L in whole blood. If the selenium test reveals a deficiency, the health insurance in some countries may pay for the selenium prescription.