Selenium (Serum/Plasma)
Selenium is an essential trace mineral measured in your serum or plasma. It supports antioxidant defenses, thyroid hormone processing, and immune function.
Selenium is part of enzymes that protect cells from damage and help your thyroid work properly. Your intake depends heavily on the selenium content of the soil where your food is grown, so levels vary by region and diet. Both too little and too much can affect health, so balance matters.
A high selenium level usually reflects supplementation or high-selenium foods. Because the safe range is relatively narrow, sustained excess can cause selenium toxicity, with effects such as hair or nail changes and digestive upset. A high result is a reason to review supplement intake with a clinician.
A low selenium level suggests inadequate intake and, over time, can affect antioxidant and thyroid-related functions. It is more likely in areas with low-selenium soil or with restricted diets.
Labs provide a reference range, and staying within it matters given selenium's narrow safety margin. A clinician can help you interpret your value and any supplement use.
Sources
Educational context only, not medical advice or a diagnosis. Reference ranges vary by lab, age and sex; always discuss your results with a clinician.