found some more info terry, REALLY GOOD:
http://www.jacn.org/cgi/content/full/20/1/1
Nutritional
Selenium Supplements: Product Types, Quality, and Safety
"
Selenium supplements contain
selenium in different chemical forms. In the majority of supplements, the
selenium is present as selenomethionine...
Current evidence favors selenomethionine over the other forms of
selenium...
Since more than 80% of the total
selenium in seleniferous corn, wheat and soybeans consists of L(+)-selenomethionine [4], this amino acid is the most appropriate supplemental form of
selenium...
In 1983... selenomethionine-rich yeast was chosen as the source of
selenium for a large-scale cancer prevention trial [17].
This trial showed that taking an extra 200 micrograms of
selenium per day significantly lowered the risks of developing prostate, lung and colorectal cancer...
In 1984, synthetic selenomethionine became available...
Since selenomethionine, like all amino acids, can exist in the L- and in the D-form and since only the L-isomer occurs naturally in foods, this form is preferable for use in supplements intended for humans...
The ‘Lowest Adverse Effect Level’ (LOAEL), defined as the ‘average daily
selenium intake causing individuals within a population to develop overt signs of toxicity,’ is believed to be in the order of 1540±653 mcg/d."
