Selenium

Question 1

Selenium

Answer 1

• A non-metallic trace element found in the body mainly as part of the antioxidant enzyme ‘glutathione peroxidase’.
• Glutathione peroxidase reduces free radicals into water and other harmless molecules.
• Selenium is found in food as an organic compound bound to the amino acids cysteine and methionine.
• Its main function is exerted in the cytosol and in mitochondria (as opposed to vitamin E , which acts in cell membranes).
• The active site of glutathione peroxidase can be occupied by mercury if in abundance, e.g. from mercury fillings and large fish.

Question 2

Selenium: Food Sources

Answer 2

Grains: whole wheat (Durum) (89.4mcg), rye, corn
Nuts & seeds: Brazil nuts (1917mccg), sunflower
Seafood: yellowfin tuna (90.6mcg) , swordfish, clams, oysters
Vegetables: garlic (14,2mcg), mushrooms
Meat & Organs: calf’s liver (35.8mcg), pork, turkey, chicken

Question 3

Selenium: Roles

Answer 3

Antioxidant
Immunity
Thyroid hormones
Reproduction

Question 4

Selenium: Antioxidant - Functions

Answer 4

• A cofactor in glutathione peroxidase (an enzyme that protects cells from free radical damage).

Question 5

Selenium: Antioxidant - Therapeutic Uses

Answer 5

• Cell antioxidant protection
• Heavy metal detox
• Acne

Question 6

Selenium: Immunity - Functions

Answer 6

• T-lymphocyte proliferation and activity.

* Antibody production.

Question 7

Selenium: Immunity - Therapeutic Uses

Answer 7

• Viral prevention
• Recovery from Colds
• Anti cancer

Question 8

Selenium: Thyroid Hormones - Functions

Answer 8

• Conversion of thyroxine (T4) to triiodothyronine (T3).

Question 9

Selenium: Thyroid Hormones - Therapeutic Uses

Answer 9

• Hypothyroidism

* Energy metabolism

Question 10

Selenium: Reprodution - Functions

Answer 10

• Selenium is needed for sperm motility

Question 11

Selenium: Reproduction - Therapeutic Uses

Answer 11

• Male fertility

Question 12

Selenium: Absorption

Answer 12

• Selenium is absorbed mostly in the duodenum (55- 85% absorption rate).
• Absorption is more efficient under conditions of deficiency.
• Selenium from plant sources (selenomethionine) is more bioavailable (>80%) than selenium from animal sources or supplements.
• Selenium homeostasis is managed primarily by the kidneys.
• Increased intake very often results in increased excretion in urine.

Question 13

Selenium Deficiency

Answer 13

• Overt Se deficiency is rare, but insufficiency may be widespread.
• Se levels decrease in response to inflammation
• An elevated T4 and lowered T3 serum level is a functional marker of Se deficiency (due to depressed iodothyronine deiodinase activity).
• Keshan disease’: an endemic cardiomyopathy that affected children in China where the soil in certain areas was known to be deficient in Se.

Question 14

Selenium Deficiency: Signs and Symptoms

Answer 14

• Deficiency signs: cardiomyopathy, muscle pain, weakness, elevated liver enzymes, growth retardation, infertility.

Question 15

Selenium Toxicity

Answer 15

Toxicity:
• Se is among the most toxic of the essential minerals and the margin between beneficial and harmful intakes is narrow.
• The TUL for adults is 300μg/day but the dose to cause toxicity is about 850-900 μg /day (combined intake food/supplements)
• Efficient methylation is important for detoxification of Selenium.
Toxicity symptoms include:
• Brittle hair and nails (or loss of nails).
• Skin lesions, dermatitis, secondary infections.
• Depression, neurological abnormalities.
• Garlic odour (from expiration of dimethylselenide)

Question 16

Selenium Nutrient Interactions

Answer 16

• In severe iodine deficiency, Se supplementation can trigger/exacerbate hypothyroidism by accelerating T4 metabolism.
• Studies suggest that supplementing with Zn/Cu may increase Se requirements.
Vitamin E
• Se deficiency aggravates the effects of Vitamin E deficiency in animal studies.
Polyunsaturated Fatty Acids
• Ingestion of large amounts of DHA and EPA increases the requirement for Selenium.