Minerals - Selenium (Se)

Question 1

Selenium (Se)

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
* It’s 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 a large fish

Question 2

Food sources

Answer 2

Key food sources / Per 100 g:
Grains: Whole wheat (durum), rye, corn / 89.4 mcg
Nuts and seeds: Brazil nuts, sunflower (79.3 mcg) / 1917 mcg
Seafood: Yellow fish tuna, swordfish, clams, oysters / 90.6 mcg
Vegetables: Garlic, mushrooms / 14.2 mcg
Meat/organs: Calf’s liver, pork, turkey, chicken / 35.8 mcg

Question 3

Functions: Antioxidant

Answer 3

Functions: Antioxidant
* A co-factor in glutathione peroxidase (an enzyme that protects cells from free radical damage)
Therapeutic uses:
* Cell antioxidant protection
* Heavy metal detox
* Acne

Question 4

Functions: Immunity

Answer 4

Functions: Immunity
* T-lymphocyte proliferation and activity
* Antibody protection
Therapeutic uses:
* Viral prevention and Recovery from colds
* Anti-cancer

Question 5

Functions: Thyroid hormones

Answer 5

Functions: Thyroid hormones
* Conversion of Thyroxine (T4) to triiodothyronine (T3)
Therapeutic uses:
* Hypothyroidism
* Energy metabolism

Question 6

Functions: Reproduction

Answer 6

Functions: Reproduction
* Selenium is needed for sperm motility
Therapeutic uses:
* Male fertility

Question 7

Absorption

Answer 7

• 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 homoeostasis is managed primarily by the kidneys
• Increased intake very often results in increased excretion in urine
  Methionine = a sulphur-based amino acid

Question 8

Deficiency

Answer 8

• Overt Se deficiency is rare, but insufficiency may be widespread
• Se levels decrease in response to inflammation
• An elevated T4 and lowered T3 level is a functional marker of Se deficiency (due to depressed iodothyronines iodothyronines 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 9

Deficiency signs

Answer 9

• Cardiomyopathy
• Muscle pain
• Weakness
• Elevated liver enzymes
• Growth retardation
• Infertility

Question 10

Toxicity

Answer 10

• 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 300 µg/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

Question 11

Toxicity symptoms

Answer 11

• Brittle hair and nails (Or loss of nails)
• Skin lesions, dermatitis, secondary infections
• Depression, neurological abnormalities
• Garlic odour (from expiration of dimethylselenide)

Question 12

Nutrient interactions: Iodine

Answer 12

• In severe iodine deficiency, Se supplementation can trigger/exacerbate hypothyroidism by accelerating T4 metabolism

Question 13

Nutrient interactions:
Zinc and Copper

Answer 13

• Studies suggest that supplementing with Zn / Cu may increase Se requirements

Question 14

Nutrient interactions: Vitamin E

Answer 14

• Se deficiency aggravates the effects of vitamin E deficiency in animal studies

Question 15

Nutrient interactions:
Polyunsaturated fatty acids

Answer 15

• Ingestion of large amounts of DHA and EPA increases the requirement for selenium

Question 16

Functions

Answer 16

Antioxidant
Immunity
Thyroid hormones
Reproduction