Get Your Personalized Supplement StackSupplement Stack Quiz

Selenium {Complex}

Also known as: Selenium (Se), selenoproteins, selenomethionine, sodium selenite, selenium-enriched yeast, Selenium

Overview

Selenium is an essential trace mineral element, atomic number 34, found naturally in soil, water, and various foods like Brazil nuts, seafood, meat, and cereals. As a supplement, it is often provided in bioavailable forms such as selenomethionine, sodium selenite, or selenium-enriched yeast. It is primarily used to support antioxidant defense, thyroid function, and immune response, and to reduce inflammation. Selenium is incorporated into selenoproteins, which are crucial for regulating redox status and thyroid hormone metabolism. Supplementation is particularly beneficial for populations with deficiency or specific health conditions, including critically ill patients, individuals with autoimmune thyroid diseases, and those experiencing depressive symptoms. Research on selenium is extensive, with numerous randomized controlled trials, systematic reviews, and meta-analyses supporting its various applications, although outcomes can vary due to population differences and heterogeneity in studies.

Benefits

Selenium supplementation offers several evidence-based benefits. In critically ill patients, parenteral selenium has shown a statistically significant reduction in all-cause mortality (RR 0.83, 95% CI 0.70–0.99, p=0.04), with a number needed to treat (NNT) of 16, indicating a modest but clinically relevant effect, especially with treatment durations exceeding 7 days. For individuals with Hashimoto thyroiditis, meta-analyses consistently demonstrate significant reductions in thyroid peroxidase antibodies (TPOAb) levels after 3–6 months of supplementation, particularly with doses over 100 μg/day, which is clinically relevant for managing autoimmune thyroid disease. Selenium has also been found to significantly decrease depressive symptoms, with moderate effect sizes observed in meta-analyses. Furthermore, it exhibits anti-inflammatory effects, significantly reducing high-sensitivity C-reactive protein (hs-CRP), a key marker of inflammation. Secondary benefits include improved oxidative stress markers and potential immune modulation. These benefits are most pronounced in selenium-deficient populations, critically ill patients, and those with autoimmune thyroid disease or depression.

How it works

Selenium exerts its effects primarily by being incorporated into selenoproteins, which are a class of proteins containing selenium in the form of selenocysteine. Key selenoproteins include glutathione peroxidases (GPx) and thioredoxin reductases (TrxR), which are crucial enzymes in the body's antioxidant defense system. These enzymes reduce oxidative stress and regulate cellular redox balance by neutralizing reactive oxygen species. Selenium also plays a vital role in thyroid hormone metabolism through iodothyronine deiodinases, another group of selenoproteins that convert thyroid hormones into their active forms. Additionally, selenium modulates immune responses and interacts with inflammatory cytokines. Its antioxidant activity helps reduce inflammation and protect cells from damage. The absorption and bioavailability of selenium vary depending on its chemical form, with organic forms like selenomethionine generally exhibiting higher bioavailability.

Side effects

Selenium is generally considered safe at recommended doses, with toxicity being rare but possible with excessive intake. Common side effects, though infrequent, include mild gastrointestinal discomfort. Uncommon side effects (1-5% incidence) may involve hair or nail brittleness and mild dermatologic reactions. Rare but severe toxicity, known as selenosis, can occur at very high doses, characterized by symptoms such as garlic breath odor, hair loss, nail changes, fatigue, irritability, and neurological symptoms. Selenium may interact with certain medications; caution is advised when co-administering with anticoagulants due to potential increased bleeding risk, and with chemotherapy agents, as it might interfere with their efficacy. Contraindications include known hypersensitivity to selenium. Individuals who are already selenium-replete should exercise caution to avoid toxicity. Special populations such as pregnant women, children, and individuals with pre-existing thyroid disorders should use selenium supplements under medical supervision and require careful monitoring.

Dosage

The minimum effective dose for benefits in autoimmune thyroid conditions is approximately 100 μg/day. Optimal dosage ranges typically fall between 100–200 μg/day for general supplementation and in most clinical trials. Higher doses may be used short-term in critical illness settings but require strict medical supervision. The Upper Tolerable Intake Level (UL) for adults is generally set at 400 μg/day to prevent toxicity. For autoimmune thyroid benefits, effects are typically observed after 3–6 months of consistent supplementation. In critical illness, benefits are linked to parenteral treatment durations exceeding 7 days. Organic forms of selenium, such as selenomethionine, are generally preferred for oral supplementation due to their superior absorption and bioavailability compared to inorganic forms like sodium selenite. The effectiveness of selenium can also be influenced by the individual's nutritional status and the presence of other antioxidants, such as vitamin E, which may enhance its effects.

FAQs

Is selenium supplementation safe long-term?

Yes, selenium supplementation is generally safe for long-term use when taken within the recommended daily doses. However, chronic intake exceeding the upper tolerable limit (400 μg/day) can lead to toxicity, known as selenosis.

When can I expect to see results from selenium supplementation?

The time to observe benefits varies. For autoimmune thyroid conditions, significant reductions in antibodies are typically seen after 3-6 months. Effects on inflammation and mood may appear earlier, but consistent use is key.

Can selenium prevent diseases?

While selenium plays a crucial role in antioxidant defense and immune function, evidence primarily supports its role in reducing mortality in critically ill patients and modulating autoimmune thyroid disease. It is not a broad disease prevention agent.

Is selenium deficiency common?

The prevalence of selenium deficiency varies geographically, largely depending on the selenium content in local soils. Deficiency is more likely in regions with low soil selenium, affecting the selenium content of crops and animal products.

Research Sources

https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0054431 – This systematic review and meta-analysis of randomized controlled trials investigated parenteral selenium supplementation in critically ill patients. It found a statistically significant reduction in all-cause mortality (RR 0.83, p=0.04) with longer treatment durations correlating with better outcomes, despite heterogeneity in dosing and patient populations.
https://www.liebertpub.com/doi/10.1089/thy.2023.0556 – This systematic review and meta-analysis of 31 cohorts of Hashimoto thyroiditis patients demonstrated a significant reduction in thyroid peroxidase antibody (TPOAb) levels, especially with selenium doses >100 μg/day, after 3–6 months of supplementation. It also noted improvements in oxidative stress markers, despite high inter-study heterogeneity.
https://www.nature.com/articles/s41598-022-05078-1 – This systematic review and meta-analysis of randomized controlled trials on depression found that selenium supplementation significantly decreased depressive symptoms. The study used appropriate statistical methods and sensitivity analyses to calculate effect sizes, despite high inter-study heterogeneity and varied depression scales.
https://pmc.ncbi.nlm.nih.gov/articles/PMC8212246/ – This systematic review and meta-analysis of randomized controlled trials indicated that selenium supplementation significantly decreased high-sensitivity C-reactive protein (hs-CRP) levels, suggesting anti-inflammatory effects. However, it found no significant effect on nitric oxide and noted variable supplementation patterns across studies, calling for further mechanistic research.