VITAMIN E
Vitamin E is found naturally in some foods, added to
others, and available as a dietary supplement. “Vitamin E” is the collective
name for a group of fat-soluble compounds with distinctive antioxidant
activities.
Naturally occurring vitamin E exists in eight chemical
forms (alpha-, beta-, gamma-, and delta-tocopherol and alpha-, beta-, gamma-,
and delta-tocotrienol) that have varying levels of biological activity. Alpha-
(or α-) tocopherol is the only form that is recognized to meet human
requirements.
Serum concentrations of vitamin E (alpha-tocopherol) depend
on the liver, which takes up the nutrient after the various forms are absorbed
from the small intestine. The liver preferentially resecretes only
alpha-tocopherol via the hepatic alpha-tocopherol transfer protein; the liver
metabolizes and excretes the other vitamin E forms. As a result, blood and
cellular concentrations of other forms of vitamin E are lower than those of
alpha-tocopherol.
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