So - selenium. This is a micronutrient found in the soil and in marine bivalves, and fixed by plants into more organically bioactive forms. Levels are extremely high in certain parts of China, Turkestan, and the Western United States. Levels are quite low in Finland, Scotland, New Zealand, and other parts of China, so that livestock must be supplemented or will fall ill. (1). According to some gardening message boards, soils here in New England aren't great, and Texas where I grew up is rather middling. And according to the various selenium sources, it is somewhat difficult to figure out how much you do get from the soil, as areas vary widely and many forms of selenium are more bioavailable than others.
What does selenium do? Well, selenium is key to one of the body's master antioxidants, glutathione peroxidase. This complex keeps the delicate polyunsaturated acids in our cell membranes from getting oxidized (rancid).
Selenium deficiency has been described in China as Keshan Disease, a type of heart problem (2). It is also thought to be a factor in gastrointestinal cancer, liver cancer, and prostate cancer. In addition, selenium in concert with iodine seems to be important to thyroid hormone production (specifically in the conversion of T4 to T3). As I've mentioned before, selenium deficiency seems to be one of the major dangers of a carelessly designed ketogenic diet, leading to death via cardiomyopathy and arrhythmia in children. Selenium deficiency was also deemed the cause of death (via cardiomyopathy) of adult patients on selenium-deficient TPN (total parenteral nutrition).
Selenium is a trace mineral. Appropriate amounts for humans are measured in micrograms rather than milligrams. People have died (from hypotension and cardiac muscle depression) via the ingestion of gram amounts of selenium, and toxicity occurs at milligram amounts. Sources indicate that the first symptoms of toxicity are hair and nail brittleness and garlic smell on the breath. The cases of death I read about involved the ingestion of "gun bluing" (2% selenious acid), so don't drink gun bluing, as selenium posioning sounds like one of the more horrific ways to die.
The bioavailability of selenium is best in plant-derived foods (grains, actually) and nuts, while the selenium in animal sources, marine sources, and mineral waters aren't as bioavailable. Fruits and vegetables, however, don't seem to have that much in the US, so if you avoid grains, the best sources are actually brazil nuts (one ounce will get you over 500 micrograms, so take it easy and have just a few at a time). Organ meats are also high in selenium. 3 oz or so of tuna, beef, cod, and chicken breast will get you around 30 mcg (though it is less bioavailable), whereas a typical grain meal (pasta, oatmeal) will net you around 10-15 mcg. Though phytic acids in grains do interfere with mineral absorption, studies of women eating wheat from selenium-rich soils showed a nice elevation in plasma levels of selenium.
The adult US RDA is 55 micrograms (though a bit higher for pregnant or breastfeeding women). (3)The doctors Jaminet recommend 200 mcg daily, and the US upper tolerable limit is 400 mcg (the level above which those nails start to get brittle, you get irritable and tired, and that breath begins to be garlicky.). On the other hand, Chinese studies of daily doses up to 1500 micrograms showed no adverse effects, nor did another study of 600 mcgs daily.
In my next post I'll review the studies of selenium and mental health. In the mean time, eat a few brazil nuts and cool it on the supplements if your breath gets garlicky or your nails start to look like this. (Actually, go see a doctor pronto if your hair falls out and your nails look like that.)
(another iPad post so forgive any bad spelling, and I'll add a few more links later!)
0 comments:
Post a Comment