Nutrition: Selenium

[liveonearth]

SELENIUM
a mineral comes in attached to aa's
antioxidant cofactor
substitutes for sulphur in cysteine
glutathione peroxidase contains an atom of selenium at active site
thyroid hormone deiodinase activates T4 to T3
other selenoproteins with unclear functions

"sparing" effect of selenium on vitamin E
relates to vit E, if low on selenium vitamin E can cover, if low on vit E extra selenium good
both prevent oxidation of tissue lipids
high amounts of one offset low amounts of the other
regenerating effect on spent antioxidatns with selenium containing thioredoxin reductase

DEFICIENCY, REGIONAL
uncommon in US due to abundant protein foods naturally high in selenium
low selenium soils suspect where deficiency is common
in NW incl WA, OR, ID, NV, northern 3/4 of CA
NE to Great Lakes region and most of Canada (not central)
down Appalachians to TN/NC/GA border
Florida, Atlantic coast
a whole province in China has low selenium, cardiomyopathy there

SOURCES
brazil nuts
shrimp
crap
salmon
halibut
enriched noodles
pork
brown rice
light meat chicken
beef
whole wheat bread
milk
walnuts, black
(harder for vegetarians to get)

SUPPLEMENTS
inorganic selenites, selenates
organic selenomethionine, mostly from yeast, yeast based supps are popular
both present in foods

RDA'S
have gone down recently
55mcg/day for males and females
15 for infants to 6 mo, 20 to 1 year, gradually increasing to adulthood

FUNCTIONS
antioxidant effects
immune function
carcinogen metabolism
metabolites effect tumor cell growth
supplementing those already well nourished makes no difference
except prostate cancer, responds well to high doses 200 mcg/day

SAFETY
severe toxitiy requiers gram amounts
UL 400 mcg/day dt mild effects of chronic use at this level: brittle hair and nails, skin rash, GI upset