Selenium : Dosing and Safety

by MedlinePlus

(Page 3 of 3)

Dosing

The below doses are based on scientific research, publications, traditional use, or expert opinion. Many herbs and supplements have not been thoroughly tested, and safety and effectiveness may not be proven. Brands may be made differently, with variable ingredients, even within the same brand. The below doses may not apply to all products. You should read product labels, and discuss doses with a qualified healthcare provider before starting therapy.

Adults (18 years and older):

U.S. Recommended Dietary Allowance (RDA) for adults (oral): 80-200mcg. Specifically: 55mcg for female adults; 70mcg for male adults; 40-70mcg for adolescent males, 45-55mcg for adolescent females; 65mcg for pregnant females; 75mcg for breast-feeding females.

Prostate cancer prevention (oral): The dose of selenium associated with reduced risk of prostate cancer in the NPC trial is 200 mcg daily.

Maximum Daily Dose (oral): 400mcg per day for those older than 14 years old (including adults and the elderly).

Intravenous (should only be used when oral therapy is not feasible, and under the direction of a qualified healthcare professional): For treatment of selenium deficiency in adults, 100mcg of elemental selenium daily for 24-31 days has been suggested. For prevention of selenium deficiency in adults, 20-40mcg of elemental selenium daily has been suggested.

Other:The following doses have been reported in research or practice, although efficacy is not necessarily proven.Asthma: 100mcg daily.Cancer prevention: 200mcg daily.Erysipelas infection: 300-1000mg daily as selenium selenite.HIV positive status: 80mcg daily.Infertility (male): 100mcg daily.Keshan disease:30mcg daily.Myocardial infarction (heart attack): 100mcg daily.Rheumatoid arthritis: 200mcg daily.

Children (younger than 18 years):

U.S. Recommended Dietary Allowance (RDA) for infants and children (oral): 10mcg for 0-6 months; 15mcg daily for 6-12 months; 20mcg for 1-6 years; 30mcg for 7-10 years; 45 mcg for 11-14 years; 50mcg for 5-18 years. Adequate intake for infants up to 6 months old may be 2.1mcg/kg/day, and for infants 7-12 months may be 2.2mcg/kg/day.

Maximum Daily Dose (oral):45mcg for 0-6 months; 60mcg for 7-12 months; 90mcg for 1-3 years; 150mcg for 4-8 years; 280mcg for 9-13 years.

Intravenous (should only be used when oral therapy is not feasible, and under the direction of a qualified healthcare professional): 3mcg of elemental selenium/kg/day intravenously for the treatment or prevention of selenium deficiency has been noted.

Other: To treat selenium deficiency in premature infants, 5mcg per day of selenized yeast has been given by a nasogastric tube.

Safety

Allergies

Selenium is a trace element, and hypersensitivity is unlikely. Avoid if known allergy/hypersensitivity to products containing selenium.

Side Effects and Warnings

Chronic toxicity: The level of selenium exposure that will cause chronic toxicity is not known, although doses 4-5 times normal dietary intake have been implicated (1 gram per day for two years has produced signs of toxicity in women). Selenium toxicity may cause gastrointestinal symptoms (nausea, vomiting, abdominal pain, diarrhea, garlic-like breath odor, metallic taste), neuromuscular-psychiatric disturbances (weakness/fatigue, lightheadedness, irritability, hyperreflexia, muscle tenderness, tremor, peripheral neuropathy), dermatologic changes (skin rash/dermatitis/flushing, fingernail loss/thickening/blotching/streaking/paronychia, hair changes/loss), liver dysfunction, kidney dysfunction, thrombocytopenia (low blood platelets), immune alterations (natural killer cell impairment), thyroid dysfunction (decreased T3), reduced sperm motility, or growth retardation. Blood selenium levels may be used to assess the degree of toxicity, with levels below 1000mcg/L usually not associated with serious toxicity, and levels above 2000mcg/L predictive of potential serious toxicity. Chronic selenium toxicity may resemble arsenic toxicity.

Acute overdose (selenosis): Acute selenium poisoning may cause fever, gastrointestinal symptoms (nausea, vomiting, pain, anorexia), liver or kidney functional impairment, respiratory distress, cardiac complications (EKG changes, increased creatine kinase levels, heart damage), and even death if levels are high enough. Other symptoms similar to chronic selenium toxicity may also occur.

Cardiovascular: Chronic low selenium levels are associated with the development of cardiomyopathy, and possibly with coronary artery disease.

Endocrine: An early toxic effect of selenium is disruption of endocrine function, including synthesis of thyroid hormones (T3), with unclear effects on growth hormone and insulin-like growth factor. Selenium deficiency may also worsen thyroid disorders related to iodine-deficiency.

Renal: Kidney failure with or without dialysis is associated with low selenium levels, and kidney transplant appears to correct selenium levels.

Genitourinary: Chronic high selenium levels may decrease sperm motility, although effects on fertility are not known.

Oncologic: Results from the Nutritional Prevention of Cancer (NPC) trial, conducted among 1312 Americans over a 13 year period, suggest that selenium supplementation (200mcg daily) given to individuals at high risk of nonmelanoma skin cancer is ineffective at preventing basal cell carcinoma, and actually increases the risk of squamous cell carcinoma and total nonmelanoma skin cancer. Therefore, selenium supplementation should be avoided in individuals at risk or with a history of nonmelanoma skin cancer.

Psychiatric: Researchers have reported high levels of selenium in children with behavioral problems, although causality has not been established. Chronic selenium toxicity has been associated with irritability or fatigue.

Pregnancy and Breastfeeding

No pregnancy category has been established for supplemental selenium intake although it is generally believed to be safe during pregnancy when consumed in amounts normally found in foods. Animal research reports that large doses of selenium may contribute to birth defects.

Selenium is excreted in breastmilk, but is generally believed to be safe to consume during lactation in amounts commonly found in foods.

Interactions

Interactions with Drugs

HMG-CoA reductase inhibitors ("Statins"): Concomitant use of selenium in combination with beta-carotene and vitamins C and E appears to decrease the effectiveness of the combination of simvastatin (Zocor®) and niacin, although long-term effects are not known. This may be due to antioxidant effects associated with selenium use. Theoretically, selenium could reduce the effectiveness of other HMG-CoA reductase inhibitors such as atorvastatin (Lipitor®), fluvastatin (Lescol®), lovastatin (Mevacor®), and pravastatin (Pravachol®).

Niacin: Concomitant use of selenium in combination with beta-carotene, vitamin C, and vitamin E appears to decrease the effectiveness of the combination of niacin and simvastatin (Zocor®). This may be due to antioxidant effects associated with selenium use.

Corticosteroids: High-dose steroid therapy may decrease plasma selenium levels.

Chemotherapy/Radiation Therapy: Concern has been raised that antioxidants may interfere with radiation therapy or some chemotherapy agents (such as alkylating agents, anthracyclines, or platinums), which themselves can depend on oxidative damage to tumor cells for anti-tumor effects. Studies of the effects of antioxidants on cancer therapies yield mixed results, with some reporting antagonistic effects (interference), others noting synergism (benefit), and most suggesting no significant interaction.This remains an area of study and controversy. In particular, selenium may reduce toxic side effects associated with chemotherapy drugs including cisplatin, doxorubicin, or bleomycin. However, until better evidence is available, selenium supplementation is not recommended during chemotherapy or radiation therapy due to potential interference. Patients considering use of selenium during chemotherapy or radiation therapy should discuss this choice with their medical and radiation oncologists.

Antacids: Agents that alter the pH of the stomach may decrease absorption of selenium.

Oral contraceptives: Selenium levels may be decreased in patients taking oral contraceptives.

Erythropoietin (EPO): Selenium has been suggested to increase the effects of erythropoietin in hemodialysis patients.

Clozapine: It has been suggested that cardiac side effects associated with clozapine use may be related to low selenium concentrations. It is not clear if assessment of selenium levels or selenium supplementation should be routine in patients taking this drug.

Interactions with Herbs and Dietary Supplements

Antioxidants: Selenium is a component of glutathione peroxidase, which possesses antioxidantactivity, and demonstrates antioxidant properties in humans. Long-term clinical benefits remain controversial. Selenium may add to the effect of other antioxidants in the body, such as vitamins A, C, and E, lycopene, green tea, soy, grape seed extract, or melatonin.

Vitamin C: There is preliminary evidence that vitamin C may be necessary for maintaining selenium levels in the body.

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