Selenium deficiency in the US is uncommon because soil selenium content is generally adequate. The classic deficiency disease, Keshan disease (a cardiomyopathy), occurred in regions of China with severely selenium-deficient soils. Significant selenium deficiency in the US is mostly seen in people with severe malabsorption, on long-term parenteral nutrition, or with HIV.
In children: Kashin-Beck disease (osteoarthropathy with joint deformities)
Possible association with hypothyroidism (selenium needed for thyroid hormone activation)
Macrocytic anemia (rare)
At-risk groups
People living in regions with severely selenium-poor soils (parts of China, New Zealand historically)
People with HIV, especially advanced disease
People on long-term total parenteral nutrition (TPN) without selenium
People with severe GI conditions affecting absorption (Crohn's, ulcerative colitis, short-bowel syndrome)
People on hemodialysis
People with severely restricted diets
Note: Brazil nuts contain extremely high selenium (~50-100+ µg per nut) — just 1-2 daily can exceed needs; supplementation is rarely necessary
When to see a doctorPersistent fatigue with hair loss, brittle nails, or unexplained heart issues — especially in someone with malabsorption or HIV — warrants serum selenium or glutathione peroxidase testing. CAUTION: selenium has a relatively narrow safety margin. Toxicity (selenosis) at intakes >400 µg/day causes hair loss, brittle nails, garlic breath, and neurological symptoms. Don't supplement above the UL without medical guidance.