Selenium is an essential trace mineral required in small quantities to support various physiological processes. The body cannot produce this mineral on its own, so it must be acquired through diet. Selenium functions primarily as a potent antioxidant, protecting cells from damage caused by free radicals and oxidative stress. An inadequate intake can lead to a cascade of observable physical and physiological issues throughout the body.
Key Physical Signs of Deficiency
One of the most noticeable outward indicators of insufficient selenium is the deterioration of hair and nail health. Individuals may experience significant hair thinning or loss, often accompanied by a loss of hair luster. The nails can become brittle, break easily, or even display white spots, reflecting the mineral’s importance for the integrity of these tissues.
A selenium deficit often manifests as compromised muscle function, leading to symptoms like generalized muscle weakness and unexplained pain. This can present as persistent fatigue and a lack of energy. Since approximately half of the body’s selenium is stored in muscle tissue, a deficiency can significantly impact energy metabolism and overall physical strength.
The immune system is also profoundly affected when selenium levels are low, as the mineral is necessary for a robust defense mechanism. A weakened immune response results in an increased susceptibility to infections and illnesses. Furthermore, selenium is required for the proper synthesis and function of thyroid hormones. A deficiency can interfere with the conversion of thyroxine (T4) to the more active triiodothyronine (T3), producing symptoms resembling hypothyroidism, such as mental fog, weight fluctuations, and persistent exhaustion.
Dietary and Environmental Causes
The most significant factor influencing selenium status is the geographical variation of the mineral in the soil. Selenium levels in crops and animal products are directly tied to the soil composition where they are grown or raised. Regions like parts of Europe, New Zealand, and certain areas of China have historically low-selenium soils, meaning a locally sourced diet may not provide adequate intake.
The concentration of selenium in the soil is determined by factors such as pH level, rainfall, and evaporation rates. In North America, soil selenium levels are generally higher, making widespread dietary deficiency less common. However, modern intensive farming practices can deplete trace minerals from the soil over time, contributing to lower selenium content in produce globally.
Specific dietary choices and medical conditions can predispose an individual to deficiency regardless of their geographic location. People following strict vegan or vegetarian diets may have lower selenium intake, as the mineral is often more readily available in animal products like seafood and meat. Conditions that cause malabsorption in the gut can inhibit the body’s ability to absorb selenium efficiently. These conditions include Crohn’s disease, ulcerative colitis, and celiac disease. Patients receiving prolonged total parenteral nutrition (TPN) or those who have undergone certain gastrointestinal surgeries, like gastric bypass, also face an elevated risk.
Testing and Restoring Selenium Levels
A suspected selenium deficiency is medically confirmed through laboratory testing, typically starting with a blood test measuring serum or plasma selenium concentrations. Levels below approximately 120 micrograms per liter are often considered indicative of insufficient status, though reference ranges vary between laboratories. Hair and nail analysis can also be used, as these tissues provide a record of long-term selenium intake over a period of months.
Correction of a confirmed deficiency usually begins with dietary modifications to increase selenium-rich food consumption. Excellent natural sources include Brazil nuts, seafood, eggs, meat, and whole grains. For individuals with a severe deficiency or impaired absorption, a healthcare provider may recommend professional supplementation.
Selenium supplements are available, but they should only be taken under medical guidance and after a test confirms a need. It is important to avoid self-diagnosing or over-supplementing, as selenium has a narrow window between a beneficial intake and a toxic level. Chronically high intake, known as selenosis, can lead to adverse effects like a metallic taste in the mouth, garlic-odor breath, and symptoms such as hair loss and brittle nails. The Tolerable Upper Intake Level (UL) for adults is set at 400 micrograms per day. Exceeding this amount without supervision increases the risk of toxicity.