Selenium is a trace mineral that is essential for vital functions, especially the antioxidant enzyme glutathione peroxidase that recycles vitamin C and E in the antioxidant cascade. Toxic hydrogen peroxide is made into harmless water by glutathione peroxidase with the help of selenium. Selenium seems to be involved in all cellular oxidative reactions including those involving copper, zinc (superoxide dismutase), and iron (catalase).
Selenium is involved in numerous enzyme and protein (selenoproteins) functions:
- Glutathione peroxidase.
- Phospholipid hydroperoxidase, reducing oxidative damage from hydrogen peroxide.
- Thioredoxin reductase, vital for regeneration of vitamin C and other anti-oxidants.
- Iodothyronine deiodinases, are vital in many steps in activation or deactivation of thyroid hormone.
- Selenoprotein P is found in vascular endothelial cells and may be protective against reactive nitrogen.
- Selenophosphate synthetase is vital in selenocysteine formation.
Numerous studies are showing benefits in improved immune function, reduced infections especially from viral infections, cancer prevention, and reduced cardiovascular disorders (atherosclerosis, heart attacks, and stroke).
SYMPTOMS OF DEFICIENCY
Due to the vital role in reducing oxidative stress, deficiency can lead to increased risks of heart disease, stroke, cancer, and depressed immune function. Inflammatory conditions like rheumatoid arthritis, eczema, psoriasis, and most other inflammatory conditions may be worse when deficient in selenium. Selenium improves natural killer cells that are important in destroying cancer and bacterial and viral infections. Selenium is important for male fertility and for normal thyroid function which is vital for brain development, especially in the womb. Selenium has been shown to benefit those with heavy metal toxicity.
Biologically active forms of selenium, like selenomethionine, seem to be much more effective than inorganic selenium salts, making food sources more important for their health benefits. Brazil nuts are particularly high in selenium, and adults may benefit from eating one or two nuts a day (avoid high intake as high selenium can be toxic).
micrograms of Selenium
Brazil nuts (1 oz = 7 nuts) 544-839
Shell fish/ fish 34-40
Meat (chicken, beef, pork) 20-33
Cottage cheese (1 cup) 20
Whole grains, wheat germ 7-15
Greens (1 cup) 11
Dairy (1 cup) 8
Lentils (1 cup) 6
SAFETY AND TOXICITY
Selenium is one of those essential nutrients that can also be toxic at high doses. While it is vital that you have some, you want to avoid taking too much. In the world, those suffering from too much selenium are typically either living in an area (parts of China) where selenium levels are high in soil and water, eating too many Brazil nuts, or taking too much selenium as a supplement.
Initial symptoms of selenium toxicity might include neurological and emotional issues, irritability, fatigue, intestinal symptoms like nausea and vomiting, diarrhea, or a rash. When your exposure is high over long periods of time (selenosis) symptoms include nail and hair brittleness and hair loss. You may detect a garlic odor to your breath.
UPPER TOLERABLE LIMITS
Children 1-3 90
Children 4-8 150
Children 9-13 280
For these reasons, pregnant moms and children should probably limit Brazil nut consumption to 1 a day (perhaps even one every other day). Adults should limit Brazil nut consumption to 1-2 a day. Having said that, if you are not getting selenium elsewhere, it may be equally as important that you consume your one Brazil nut daily. The RDA (recommended daily allowance) for infants is 15-20 micrograms daily, children 20-40, and adults 55-70.
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