selenium (generic name)
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SafetyDISCLAIMER: Many complementary techniques are practiced by healthcare professionals with formal training, in accordance with the standards of national organizations. However, this is not universally the case, and adverse effects are possible. Due to limited research, in some cases only limited safety information is available.
Selenium is a trace element and hypersensitivity is unlikely. Avoid individuals with a known allergy/hypersensitivity to products containing selenium.
Side Effects and Warnings
The level of selenium exposure that will cause chronic toxicity is not known. Selenium toxicity may cause gastrointestinal symptoms (nausea, vomiting, abdominal pain, diarrhea, garlic-like breath odor, and metallic taste), neuromuscular-psychiatric disturbances (weakness/fatigue, lightheadedness, irritability, hyperreflexia, muscle tenderness, tremor, and peripheral neuropathy), dermatologic changes (skin rash/dermatitis/flushing, fingernail loss/thickening/blotching/streaking/paronychia, and 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.
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.
Chronic low selenium levels are associated with the development of cardiomyopathy and possibly with coronary artery disease. Selenium supplementation in selenium-deficient rats may lead to increased serum homocysteine, which is linked to cardiovascular disease. However, human studies suggest that this does not occur in healthy humans.
There have been numerous reports of adverse reactions to shampoos and lotions containing 2.5% selenium sulfide. Selenium applied topically apparently is not absorbed significantly into the bloodstream.
In animals, selenium deprivation can result in cataracts. Cataracts can be induced by administering selenium in doses several hundred times higher than the daily requirement. At present, there is not enough human evidence that selenium supplementation beyond the normal dietary requirement will affect the rate of cataract formation.
Results from the Nutritional Prevention of Cancer (NPC) trial, conducted among 1,312 Americans over a 13-year period, suggest that selenium supplementation 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.
Researchers have reported high levels of selenium in children with behavioral problems, although causality has not been established.
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. Studies suggest that a daily intake of 50-75 micrograms is adequate during lactation.
Animal research reports that large doses of selenium may contribute to birth defects.
Selenium is excreted in breast milk, but it is generally believed to be safe to consume during lactation in amounts commonly found in foods. Studies have shown that different types of selenium consumed may have varying affects on the selenium content of breast milk. For example, selenomethionine appears to increase milk selenium concentrations more significantly than selenium-enriched yeast.