⚠️ Educational only. LabPlain does not provide medical advice or diagnosis. Always discuss your specific results with your healthcare provider.
What this test measures
Selenium is an essential trace mineral that your body requires in small amounts to function correctly. It is a core building block for selenoproteins, which are special proteins that function as powerful antioxidants to protect your cells from damage caused by oxidative stress.
Beyond acting as a cellular shield, selenium plays a critical role in supporting a healthy immune system and is highly concentrated in the thyroid gland, where it helps convert thyroid hormones into their active forms. Your body cannot produce selenium on its own, so it must be absorbed from your diet through foods like Brazil nuts, seafood, meat, and whole grains.
Doctors typically order a selenium blood test if they suspect a deficiency due to severe malabsorption or long-term specialized diets, or if they are investigating potential industrial or accidental overexposure (toxicity).
Normal reference range
Adult Standard Range: 70–150 mcg/L
A normal selenium level indicates that your body is getting an adequate supply of this trace mineral to support regular cellular defense, immune response, and thyroid health without reaching levels that stress your tissues.
Reference ranges can vary slightly between different laboratories based on the specific testing equipment and geographic demographics. Always evaluate your final result using the reference numbers printed directly on your official laboratory report.
📊 Geographical Variations
The selenium content in food depends heavily on the soil where the food was grown or raised. Because soil levels vary drastically worldwide, baseline dietary intake differs significantly by region, which your doctor may take into context when looking at your results.
What your result might indicate
↑ If High
An elevated selenium level may point to excessive dietary intake—often from eating too many selenium-dense foods like Brazil nuts—or high-dose dietary supplementation. In rarer cases, it may reflect acute or chronic environmental or occupational exposure.
↓ If Low
A low selenium level may suggest inadequate dietary intake or a long-term nutritional deficit. It is frequently associated with severe gastrointestinal malabsorption conditions or prolonged dependency on specialized medical nutrition that lacks sufficient trace elements.
Symptoms associated with abnormal selenium
↑ High Selenium Symptoms
Garlic-like odor on the breath
Brittle hair or sudden hair loss
Nails that split, crack, or fall off
Nausea, vomiting, or metallic taste
Fatigue and general irritability
Numbness or tingling in the extremities
Skin rashes or lesions
↓ Low Selenium Symptoms
Unexplained muscle pain or weakness
Sluggishness or symptoms of underactive thyroid
Frequent illnesses or weakened immune response
Hair loss or premature thinning
Reproductive challenges or infertility
Mental fatigue or poor concentration
Common causes of abnormal selenium
What can raise selenium?
The most common cause of high selenium levels is over-supplementation. Because selenium is a popular ingredient in multi-vitamins and hair, skin, and nail supplements, taking multiple products concurrently can easily push levels into an elevated range. Eating extreme quantities of high-selenium foods, such as multiple Brazil nuts every single day, can also cause a significant rise.
Less common but more severe causes include environmental or industrial exposure, where accidental inhalation or skin contact with selenium compounds occurs in specific workplaces.
What can lower selenium?
Low selenium levels are generally seen in individuals who live in geographic regions where the natural soil content is highly depleted of minerals, resulting in a low-selenium local food supply. Additionally, chronic digestive disorders such as Crohn’s disease, celiac disease, or surgical removal of parts of the stomach can severely limit the body's ability to absorb nutrients from food.
Individuals undergoing long-term intravenous feeding (total parenteral nutrition) without proper mineral fortification or those dealing with severe, long-term malnutrition may also show depleted levels.
Tests often ordered alongside selenium
Because selenium functions closely alongside other nutritional and hormonal markers, your provider may evaluate it in combination with:
TSH, Free T3, & Free T4 — to evaluate how your thyroid is running, as selenium is critical for thyroid hormone activation.
Zinc & Copper Blood Tests — other trace minerals that work in tandem with selenium to balance your body's overall antioxidant systems.
Vitamin E Levels — an essential antioxidant vitamin that works synergistically with selenium to protect cell walls from damage.
CBC (Complete Blood Count) — to screen for generalized cellular health and evaluate immune system markers.
What to do next
An isolated selenium reading outside the standard range provides a helpful clue, but it shouldn't be a cause for panic. Mineral levels shift gradually over time in response to your ongoing dietary habits, digestive health, and environment. Your doctor will weigh this number against your daily routine, existing physical symptoms, and potentially other nutrient markers to determine if any adjustments are truly necessary.
Questions to ask your doctor
01Could my current daily diet or supplements explain my selenium level?
02Do my symptoms align with a selenium deficiency or excess, or should we look elsewhere?
03Is this result showing an impact on my thyroid function or general hormone levels?
04Should I make specific adjustments to what I eat, or should I stop taking certain vitamins?
05Do we need to repeat this test in a few weeks or months to track the trend?
Frequently asked questions
Can eating too many Brazil nuts cause selenium toxicity?
Yes. Brazil nuts are exceptionally rich in selenium. Eating just a few nuts can easily exceed your daily recommended intake. Consuming large quantities of them consistently over a long period can lead to mild toxicity symptoms like brittle nails or hair loss.
Does selenium affect my thyroid directly?
Selenium does not make thyroid hormones on its own, but it is highly concentrated in thyroid tissue and is necessary for the biochemical enzymes that convert thyroid hormones into their usable, active forms throughout the body.
How long does it take for selenium levels to change?
Because selenium is integrated into your body's proteins and tissues, serum levels usually adjust gradually over several weeks to a couple of months following targeted changes in your diet or supplement intake.
Can a standard multivitamin cause high selenium?
A standard, balanced multivitamin generally contains safe daily amounts. However, if you combine a multivitamin with specialized hair/nail supplements or high-dose mineral pills, your cumulative intake may inadvertently climb above the optimal range.