Selenium is a trace mineral—meaning the body only needs tiny amounts—but its impact on health is enormous. Unlike copper and iron, selenium was discovered relatively recently, and its biological importance was a surprise to scientists. The story of selenium begins in 1817, when Swedish chemist Jöns Jacob Berzelius discovered the element while analyzing a sample of sulfuric acid. He named it “selenium” after Selene, the Greek goddess of the moon, because of its silvery-gray appearance.
For over a century, selenium was thought to be toxic—even deadly. In the 1930s, farmers in the Great Plains of the United States noticed that their livestock was dying from a mysterious disease: they lost their hair, developed muscle weakness, and eventually died. Scientists traced the problem to high levels of selenium in the soil, which the animals ingested through plants. This led to selenium being labeled a “poisonous mineral”—a reputation that lasted until the 1950s.
The turning point came in 1957, when nutritionist Klaus Schwarz conducted a groundbreaking experiment at the University of California, Davis. Schwarz was studying liver necrosis (liver cell death) in laboratory rats, which was thought to be caused by a toxin. To his surprise, he found that adding tiny amounts of selenium to the rats’ diet prevented the disease. This was the first proof that selenium is essential for animal (and human) health—a discovery that upended decades of scientific belief.
In the 1970s, researchers made another key discovery: selenium is a component of glutathione peroxidase, an enzyme that acts as a powerful antioxidant. This enzyme protects cells from damage caused by free radicals—unstable molecules that contribute to aging, chronic diseases, and cancer. A 1989 study published in the New England Journal of Medicine found that people with higher selenium levels had a lower risk of certain cancers, including lung and prostate cancer, sparking widespread interest in selenium’s role in disease prevention.
Today, we know selenium also plays a critical role in thyroid health: it helps convert thyroid hormones into their active form, regulating metabolism, energy levels, and mood. It also supports reproductive health, DNA synthesis, and a healthy immune system. The story of selenium is a reminder that even the smallest nutrients can have the biggest impacts—and that scientific discoveries often come from challenging conventional wisdom.
