Selenium

Scientific studies (revies articles) on the relationship between selenium and disease prevention:
A review article (a collection of scientific studies on a specific topic) of randomized, placebo-controlled double blind clinical trials (RCTs) will answer the following question:
"Do taking dietary supplements make sense?" Yes for a positive conclusion and no for a negative conclusion.

A review article (a collection of scientific studies on a specific topic) of cohort studies or case-control studies will answer the following question:
"Should I change my diet?".

1. High selenium dietary intake reduces hip fracture
2. Selenium supplementation reduces postpartum depression
3. A low selenium level increases breast cancer
4. Higher selenium and lower zinc level increase risk of vitiligo
5. Higher levels of selenium in cerebrospinal fluid increase Parkinson's disease
6. Selenium supplementation decreases hs-CRP level among patients with metabolic diseases
7. Low selenium and zinc levels increase rheumatoid arthritis
8. Serum selenium is lower in tuberculosis patients
9. A diet with high antioxidant properties reduces all-cause mortality risk
10. A low selenium level in the brain increases Alzheimer’s disease
11. High serum selenium levels reduce risk of cervical cancer among women
12. Circulatory selenium concentration is lower in Alzheimer's disease patients
13. Vitamin and antioxidant supplements have no overall preventive effect against bladder cancer
14. Elevated serum selenium levels may decrease high-grade prostate cancer among current and former smokers

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• Selenium is a trace mineral.
• In foods, selenium is generally present as the amino acid derivatives selenomethionine and selenocysteine.
• Brewer's yeast, wheat germ, liver, butter, fish (mackerel, tuna, halibut, flounder, herring, smelts) and shellfish (oysters, scallops and lobster), garlic, whole grains, sunflower seeds and Brazil nuts are good sources of selenium.
• Selenium levels in food depend on how much selenium was in the soil where the food was grown.
  Selenium is destroyed when foods are refined or processed.
• Selenium bioavailability is affected by the chemical form of selenium (organic or inorganic).
  Organic selenium is more bioavailable than inorganic selenium and also retains in tissues more.
  Similarly, the effectiveness of inorganic supplements of selenium has been reported to be less than that of organic supplements.
• The biologically active form of selenium is selenocysteine. Selenocysteine is incorporated into selenoproteins, of which over thirty have been identified to date.
  The selenoproteins include the glutathione peroxidases, which protect against oxidative damage, the iodothyronine deiodinases (involved in the production of the hormone triiodothyronine from thyroxine), selenoprotein P (which is involved in antioxidant and transport functions) and the thioredoxin reductases (maintenance of the intracellular redox state).
• Selenium is most notable for its antioxidant properties.
• There are interactions between selenium and other nutrients, such as iodine and vitamin E.
• Selenium deficiency is rare.
  Selenium deficiency can lead to heart disease, Keshan disease, hypothyroidism and a weakened immune system.
  Selenium intakes of at least 20 mcg/day protect adults from Keshan disease.
• A deficiency occurs at doses lower than 30 mcg per day.
• The RDA is 50-200 micrograms of selenium a day.
• The tolerable upper intake level (UL) for selenium is 400 mcg per day.
  There is a relatively narrow range of selenium intake between toxicity (>400 mcg per day) and deficiency (30 mcg per day). Therefore, taking supplements is not without risk.
• Too much selenium in the blood can cause a condition called selenosis. Selenosis can cause hair loss, nail problems, nausea, irritability, fatigue and mild nerve damage.
• Plasma or serum selenium concentrations of 8 micrograms (mcg)/dL or higher in healthy people typically meet needs for selenoprotein synthesis.
• The normal concentration in adult human blood serum is 70 to 150 ng/mL with a population mean value of 98 ng/mL.
• In the state of selenium deficiency associated with loss of glutathione peroxidase activity, the serum concentration is usually 40 ng/mL.
• The most abundant selenoproteins in blood are selenoprotein P, which accounts for approximately 50% of plasma selenium and GPx, which accounts for 10–30% of plasma selenium.
• The human body's content of selenium is believed to be in the 13-20 milligram range or sufficient for approximately 3 years.
• Skeletal muscle is the major site of selenium storage, accounting for approximately 28% to 46% of the total selenium pool.