Selenium

Selenium is an essential trace mineral that the human body requires in small amounts for critical physiological functions, including antioxidant defense and thyroid hormone metabolism. In the context of a plant-based diet, selenium is naturally present in soil and taken up by plants, so its content in foods varies geographically. Consumers encounter selenium in whole foods like Brazil nuts, sunflower seeds, mushrooms, and whole grains, as well as in fortified products such as plant-based milks and cereals. Because selenium levels in crops depend on regional soil selenium concentrations, dietary intake can differ significantly depending on where foods are grown.

In practice, selenium functions as a key component of selenoproteins, which are enzymes that protect cells from oxidative damage and regulate thyroid activity. The most well-known selenoprotein is glutathione peroxidase, which neutralizes hydrogen peroxide and lipid peroxides. Brazil nuts are exceptionally rich in selenium—just one nut can provide over 100% of the daily recommended intake—but their selenium content mirrors the soil of the Amazon basin where they are harvested. In regions with selenium-poor soils, such as parts of Europe and China, plant foods may contain very low levels, making supplementation or consumption of imported foods necessary for adequate intake.

For someone eating a plant-based diet, selenium matters because it is not as ubiquitous in plant foods as in animal products like meat and seafood, which typically accumulate selenium more reliably. A single Brazil nut daily can meet selenium needs, but overconsumption risks toxicity, as the upper tolerable limit is only 400 micrograms per day. Relying solely on local produce in selenium-deficient areas may lead to insufficiency, so it is prudent to include a variety of selenium-rich plant foods or consider a supplement. The nuance is that selenium requirements are small, and both deficiency and excess have adverse health effects, making balance key.