Usage
Selenomethionine, an organic form of selenium, is primarily used as a dietary supplement to prevent or treat selenium deficiency. It plays a crucial role in thyroid hormone metabolism and protects cells from oxidative damage. Although some research suggests potential benefits for conditions like hypothyroidism, autoimmune thyroiditis, ulcerative colitis, heart disease, and cognitive decline, further research is needed to confirm these effects. It is classified as a dietary supplement/nutritional supplement rather than a drug belonging to a specific pharmacological class. Its mechanism of action involves being incorporated into proteins as selenoproteins, functioning as antioxidants that neutralize free radicals and protect against cellular damage.
Alternate Names
- SeMet
- L-selenomethionine
- Selenium (as L-selenomethionine)
Brand names vary depending on the manufacturer.
How It Works
Pharmacodynamics: Selenomethionine is incorporated into proteins to form selenoproteins, which act as antioxidants. Key selenoproteins include glutathione peroxidases and iodothyronine deiodinases, which are crucial for thyroid hormone metabolism. These enzymes neutralize free radicals, thereby protecting cellular components like DNA and cell membranes from oxidative damage.
Pharmacokinetics: Selenomethionine is absorbed in the small intestine through the same pathways as methionine. It is then metabolized, with some selenium being incorporated into selenoproteins and the rest being excreted mainly through urine, but also feces and exhaled air.
Mode of Action: Selenomethionine acts primarily by becoming integrated into selenoproteins. Glutathione peroxidases, a major group of selenoproteins, catalyze the reduction of hydrogen peroxide and lipid peroxides, thus preventing oxidative stress. Iodothyronine deiodinases convert thyroxine (T4) to the active thyroid hormone triiodothyronine (T3).
Elimination Pathways: Selenium is primarily excreted in urine as various metabolites. Other elimination routes include feces and exhaled air (as dimethyl selenide).
Dosage
Standard Dosage
Adults: The recommended daily allowance (RDA) for adults is 55 mcg/day. Supplemental doses typically range from 50 mcg to 200 mcg per day. The tolerable upper intake level (UL) is 400 mcg/day from all sources combined.
Children: Recommended daily intakes vary with age: 15-20 mcg/day for infants (birth to 12 months), 20-55 mcg/day for children and adolescents (1-18 years).
Special Cases:
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Elderly Patients: The RDA for selenium remains 55 mcg/day. However, factors such as reduced nutrient absorption and potential for drug interactions need to be considered.
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Patients with Renal Impairment: Dose adjustments may be needed. Careful monitoring of selenium levels is advisable.
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Patients with Hepatic Dysfunction: Dose modification might be necessary. Careful monitoring is important.
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Patients with Comorbid Conditions: Individuals with diabetes, skin cancer, or autoimmune diseases should exercise caution and consult a doctor before using selenium supplements.
Clinical Use Cases
Selenomethionine is not typically used in clinical settings like intubation, surgical procedures, mechanical ventilation, or ICUs. It is primarily a dietary supplement to prevent or treat selenium deficiency.
Dosage Adjustments
Dose adjustments may be required based on individual needs, existing medical conditions, and drug interactions. Renal or hepatic impairment may necessitate lower doses.
Side Effects
Common Side Effects
At appropriate doses, side effects are uncommon. Selenomethionine may cause gastrointestinal upset, garlic-like breath odor, fatigue, hair loss, and brittle nails at higher doses.
Rare but Serious Side Effects
Selenium toxicity can occur with excessive intake. Severe symptoms include peripheral neuropathy, tremors, and organ damage.
Long-Term Effects
Long-term use of high doses of selenium might increase the risk of type 2 diabetes and some cancers.
Adverse Drug Reactions (ADR)
Rarely, allergic reactions can occur, including rash, itching, swelling, and difficulty breathing.
Contraindications
- Hypersensitivity to selenium
- Severe renal or hepatic impairment (relative contraindication)
- History of skin cancer (relative contraindication)
- Autoimmune diseases (relative contraindication)
Drug Interactions
Selenium can interact with various medications, including:
- Chemotherapy drugs: Selenium may affect the efficacy of chemotherapy.
- Blood thinners: Selenium might increase bleeding risk with anticoagulants like warfarin.
- Cholesterol-lowering drugs: Selenium may reduce the effectiveness of statins.
- Birth control pills: May increase selenium levels.
Pregnancy and Breastfeeding
Selenium is essential during pregnancy and breastfeeding. The RDA for pregnant women is 60 mcg/day, and for breastfeeding women, it is 70 mcg/day. However, excessive selenium can be harmful to the fetus. It is recommended not to exceed the UL of 400 mcg/day from all sources.
Drug Profile Summary
- Mechanism of Action: Antioxidant via incorporation into selenoproteins (e.g., glutathione peroxidases, iodothyronine deiodinases).
- Side Effects: Garlic breath, hair loss, brittle nails, gastrointestinal upset (at high doses); selenium toxicity with excessive intake.
- Contraindications: Hypersensitivity to selenium.
- Drug Interactions: Chemotherapy drugs, blood thinners, cholesterol-lowering drugs, birth control pills.
- Pregnancy & Breastfeeding: Essential nutrient within RDA limits (60 mcg/day during pregnancy, 70 mcg/day during breastfeeding); avoid excessive intake.
- Dosage: 55 mcg/day for adults. Pediatric doses vary with age.
- Monitoring Parameters: Serum selenium levels, thyroid hormone levels.
Popular Combinations
Selenium is sometimes combined with vitamin E to enhance antioxidant effects, or with iodine to improve thyroid function in patients with Hashimoto’s disease. Myo-inositol is also occasionally used in conjunction with selenium to treat hypothyroidism.
Precautions
- General Precautions: Monitor serum selenium levels. Avoid excessive intake.
- Specific Populations: Pregnant and breastfeeding women should stick to the recommended intake. Individuals with diabetes, renal impairment, hepatic dysfunction, autoimmune diseases, or history of skin cancer should exercise caution and consult their healthcare provider before supplementing with selenium.
- Lifestyle Considerations: A healthy diet generally provides adequate selenium. Smoking and alcohol consumption may decrease selenium levels.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Selenomethionine?
A: The RDA for adults is 55 mcg/day, increasing to 60 mcg/day during pregnancy and 70 mcg/day while breastfeeding. Pediatric dosages vary based on age.
Q2: What are the signs of selenium deficiency?
A: Selenium deficiency is rare but can manifest as muscle weakness, cardiomyopathy, and impaired thyroid function.
Q3: What are the symptoms of selenium toxicity?
A: Selenium toxicity can cause garlic breath, hair loss, brittle nails, gastrointestinal issues, fatigue, and nervous system problems. Severe toxicity can lead to organ damage.
Q4: Can I take Selenomethionine if I am pregnant or breastfeeding?
A: Selenium is an essential nutrient during pregnancy and lactation. However, it is crucial to stay within the RDA (60 mcg/day during pregnancy, 70 mcg/day during breastfeeding) to avoid potential harm from excessive selenium.
Q5: Does Selenomethionine interact with any medications?
A: Yes, it can interact with certain medications, such as chemotherapy drugs, blood thinners, cholesterol-lowering statin drugs, and birth control pills.
Q6: Can Selenomethionine help with thyroid problems?
A: Selenium is crucial for thyroid hormone metabolism. Some studies suggest that selenium supplementation might benefit individuals with Hashimoto’s thyroiditis and hypothyroidism, particularly when iodine deficiency is present. However, more research is needed.
Q7: Is it safe to take Selenomethionine long-term?
A: Long-term use of high doses of selenium may increase the risk of type 2 diabetes. It is generally recommended not to exceed the UL of 400 mcg/day from all sources combined.
Q8: What foods are rich in selenium?
A: Brazil nuts, seafood, meat, poultry, eggs, whole grains, and some vegetables are good dietary sources of selenium.
A: Selenomethionine is absorbed similarly to methionine and can be incorporated into proteins. It is ultimately metabolized and excreted mainly in urine, but also through feces and exhaled air.
Q10: What are the potential benefits of Selenomethionine for ulcerative colitis?
A: Some research suggests that selenomethionine might decrease inflammation and improve symptoms in patients with ulcerative colitis, but further studies are required.
