Selenious Acid
Also known as: Selenious acid, Selenous acid, H2SeO3
Overview
Selenious acid is an inorganic selenium compound used as a dietary supplement to provide selenium, an essential trace mineral vital for numerous biological functions. Selenium is naturally present in various foods like Brazil nuts, seafood, meats, and cereals. Selenious acid is a specific form utilized in supplements and for food fortification. Its primary applications include correcting selenium deficiency and supporting the body's antioxidant defense systems, thyroid function, and immune health. Extensive research, including numerous randomized controlled trials (RCTs) and meta-analyses, has evaluated its effects on conditions such as thyroid disease, immune function, metabolic syndrome, depression, and cancer risk. The quality of evidence for selenious acid's benefits varies by indication but includes high-quality systematic reviews and meta-analyses, underscoring its established role in health.
Benefits
Selenious acid supplementation offers several evidence-based benefits. For thyroid health, particularly in Hashimoto’s thyroiditis, doses above 100 μg/day significantly reduce thyroid peroxidase antibodies (TPOAb), indicating a reduction in autoimmune activity, supported by high-quality meta-analyses. In terms of immune function, selenium supplementation improves various immunity-related outcomes by enhancing antioxidant capacity and reducing oxidative stress markers, as shown in experimental human studies. Meta-analyses also indicate that selenium supplementation significantly decreases depressive symptoms, suggesting a role in mood regulation. For metabolic syndrome, a U-shaped relationship exists between blood selenium levels and risk, with optimal levels around 160 μg/L associated with the lowest risk. Furthermore, selenium intake is linked to a decreased risk of digestive system cancers and all-cause mortality, though the quality of evidence for these associations varies.
How it works
Selenious acid functions by providing selenium, which is crucial for the synthesis of selenoproteins. These include glutathione peroxidases and thioredoxin reductases, key enzymes that protect cells from oxidative damage. Selenium also modulates immune responses by influencing cytokine production and enhancing the body's overall antioxidant defenses. Furthermore, it plays a vital role in thyroid hormone metabolism by regulating deiodinase enzymes, which are responsible for converting inactive thyroxine (T4) into the active triiodothyronine (T3) hormone. The absorption of selenium from selenious acid is efficient, though its overall bioavailability can be influenced by the specific dose and chemical form.
Side effects
Selenium supplementation, including selenious acid, is generally safe when taken within recommended doses, typically up to 400 μg/day. Common side effects, occurring in more than 5% of users, are rare but may include mild gastrointestinal discomfort. Uncommon side effects (1-5% frequency) can include hair loss or nail brittleness, usually associated with excessive intake. Rare side effects (less than 1% frequency) at toxic doses exceeding 400 μg/day can lead to selenosis, characterized by symptoms such as a garlic breath odor, fatigue, and neurological issues. Selenium can interact with certain medications, such as chemotherapy agents, and should be used cautiously in individuals with pre-existing selenium excess or specific thyroid disorders. Special populations, including pregnant women, require careful dosing due to the potential for toxicity at higher levels.
Dosage
The minimum effective dose of selenious acid for reducing thyroid antibodies and achieving immune benefits is approximately 100 μg/day. The optimal dosage typically ranges from 100 to 200 μg/day, depending on the specific indication and an individual's baseline selenium status. The maximum safe dose to avoid toxicity is generally considered to be 400 μg/day. Dosing timing is flexible, but consistent daily intake is recommended for sustained benefits. Selenious acid is typically administered orally in supplement form. Absorption is enhanced when taken with food, and while no specific cofactors are strictly required, adequate overall nutrition supports the body's utilization of selenium.
FAQs
Is selenious acid supplementation safe?
Yes, at recommended doses (100–200 μg/day), selenious acid is safe for most adults. Toxicity occurs only at high doses (>400 μg/day), leading to symptoms like garlic breath and fatigue.
How long does it take to see benefits from selenious acid?
Noticeable benefits, such as reduction in thyroid antibodies and improvements in mood, are typically observed after 3 to 6 months of consistent supplementation.
Can selenious acid prevent disease?
Selenium may reduce the risk of certain cancers and improve immune function, but it should not be considered a standalone preventive treatment for any disease.
Is taking more selenium always better?
No, more selenium is not always better. Excess selenium can increase the risk of metabolic syndrome and lead to toxicity, so it's crucial to stay within recommended dosage ranges.
Research Sources
- https://www.liebertpub.com/doi/10.1089/thy.2023.0556 – This systematic review and meta-analysis, encompassing 31 cohorts, found that selenium supplementation, particularly at doses above 100 μg/day, significantly reduces thyroid peroxidase antibodies (TPOAb) and oxidative stress markers in patients with Hashimoto’s thyroiditis. Despite high heterogeneity, it's a high-quality analysis supporting selenium's role in autoimmune thyroid disease.
- https://www.frontiersin.org/journals/nutrition/articles/10.3389/fnut.2024.1451342/full – This systematic review and dose-response meta-analysis, involving 16,779 participants, revealed a U-shaped association between blood selenium levels and metabolic syndrome risk. The lowest risk was observed at blood selenium levels around 160 μg/L, indicating that both low and excessively high levels can increase risk. The study is of moderate quality with robust sensitivity analyses.
- https://www.nature.com/articles/s41598-022-05078-1 – This systematic review and meta-analysis of multiple RCTs and observational studies concluded that selenium supplementation significantly decreases depressive symptoms. Despite high heterogeneity due to different depression scales used, it is considered a high-quality meta-analysis with statistical rigor, suggesting a role for selenium in mood regulation.
- https://pmc.ncbi.nlm.nih.gov/articles/PMC10534049/ – This umbrella review, synthesizing 76 meta-analyses, found links between selenium intake and reduced risk of digestive system cancers, as well as all-cause mortality and depression. While comprehensive, the quality of included studies varied, and publication bias was a potential limitation, suggesting caution in interpreting some findings.
- https://pubmed.ncbi.nlm.nih.gov/36789948/ – This systematic review and meta-analysis of experimental human studies demonstrated that selenium supplementation improves various immune markers and enhances antioxidant status. It provides high-quality experimental evidence supporting selenium's role in bolstering immune function and reducing oxidative stress, though it noted a limited number of large-sample RCTs.
