15 Nutritional Deficiencies That Develop Slowly and Are Frequently Missed

12. Selenium Deficiency - The Antioxidant Guardian

Selenium deficiency is a global concern affecting an estimated one billion people worldwide, particularly in regions with selenium-depleted soils, yet it often remains undiagnosed due to its subtle onset and nonspecific symptoms. Selenium is an essential trace element that functions as a component of selenoproteins, which have antioxidant properties and play roles in thyroid hormone metabolism, immune function, and reproduction. The deficiency develops slowly and can manifest as increased susceptibility to viral infections, muscle weakness, fatigue, hair loss, and white spots on fingernails. In severe cases, selenium deficiency can lead to cardiomyopathy (Keshan disease) and joint problems (Kashin-Beck disease), conditions that were first identified in selenium-deficient regions of China. Selenium status is closely linked to thyroid function, as selenoproteins are essential for thyroid hormone metabolism, and deficiency can exacerbate iodine deficiency disorders. The selenium content of foods varies dramatically based on soil selenium levels, making geographic location a significant factor in selenium intake. Brazil nuts are exceptionally high in selenium, while other good sources include seafood, meat, and grains grown in selenium-rich soils. Factors that may increase selenium requirements include pregnancy, breastfeeding, HIV infection, and exposure to heavy metals. Assessment of selenium status is typically done through blood or toenail selenium measurements, with plasma selenium reflecting recent intake and toenail selenium indicating longer-term status.