Selenium is another one of the trace minerals that is required by the human body in very small amounts. It is mainly used by the body to form various proteins that have antioxidant properties.
The mineral is available in the water and soil, meaning that its concentration in the food depends on where it was grown and raised as various places across the world have different soil compositions.
Fish, crab, poultry, liver and wheat are usually good natural sources of selenium. Brazil nuts, beef, eggs and some dairy and grain products can also be used as selenium sources.
Selenium is used to make proteins called selenoproteins. These are then incorporated into various enzymes, like, glutathione peroxidase, thioredoxin reductase, deiodinase enzymes.
Glutathione peroxidase, for example, works by converting hydroxyl radicals and hydrogen peroxide into water. Thioredoxin reductase enzyme is responsible for regulating metabolism.
Conversion of thyroid hormones from one form to another also requires selenium in deiodinase enzymes. Other functions that are affected by enzymes that contain selenium are immune function and male fertility.
Due to selenium compounds being very effective antioxidants, reduced levels of the mineral can lead to possible development of chronic diseases. Selenium deficiency can contribute to hypothyroidism (a type of heart disease) and weaken the immune system as well as reduce body’s ability to fight cancer.
According to research, the deficiency is not the actual cause of any disease. As the body’s immune system is weakened, it simply becomes more susceptible to various illnesses.
Selenium deficiency cases are usually only diagnosed in areas with very poor soils or in people who suffer from serious gastrointestinal illnesses as it impairs selenium absorption in the body.
Selenosis is a condition caused by high concentration of selenium in the blood (over 100µg/dL). Symptoms associated with this illness are hair loss, nail discoloration, irritability, fatigue, gastrointestinal problems and possibly even mild nerve damage.
Fortunately, selenosis cases are very rare and are usually related to industrial accidents. As selenium levels in the soil are usually low, dietary intake of the mineral alone cannot result in any adverse health effects.
Long term selenium supplementation or too high doses have been associated in some cases with increased risk of developing prostate and skin cancer; it can also worsen iodine deficiency effects and decrease sperms ability to move causing fertility problems.
Recommendations for Intake
The Tolerable Upper Intake Levels for selenium intake are set at 400 µg per day for adults and children older than 14 years and 25-280 µg per day for younger children depending on their age. Selenium intake up to these levels is considered safe and should not result in any adverse health effects.
Supplementation of the mineral is advised only in special cases after consulting a health professional or if prescribed. A varied and balanced diet should provide enough selenium to meet your body’s requirements and currently Recommended Daily Allowances are set at:
- Adults and children over 14 years of age– 55 µg
- Children (9-13 years) – 40 µg
- Children (4-8 years) – 30 µg
- Children (1-3 years) – 20 µg
- Infants (7-12 months) – 20 µg
- Infants (0-6 months) – 15 µg