Selenium is an ultratrace essential nutrient found in meats, seafood, eggs, milk, and some enriched cereals. It plays an important role in wound healing through mediating keratinocyte adhesion to the basement membrane. In addition, it is also involved in immune, reproductive, and endocrine functions. Selenium is thought to have anti-inflammatory properties against reactive oxidating species in aging.

A history of bariatric surgery, dieting, severe illness (COVID-19, HIV), pregnancy, protein-losing enteropathies, malabsorptive disorders, and parenteral nutrition without selenium supplementation are risk factors for selenium deficiency. Hemodialysis patients are also at risk for selenium deficiency due to selenium removal via dialysis or uremia-induced anorexia. 

Individuals with selenium deficiency present with skin pigment changes, nail changes, and xerosis. Severe selenium deficiency can present with skeletal muscle dysfunction and cardiomyopathy, increased susceptibility to infections, as well as macrocytosis.

An endemic cardiomyopathy (Keshan disease) affecting children and those of childbearing potential in parts of China has been linked to selenium deficiency.