Abstract
Inorganic selenium (selenite and selenate)
and selenium yeast (Se-yeast) are the only approved
sources of supplemental selenium (Se) in the U.S.
The predominant form of Se in Se-yeast is selenomethionine
(Se-met). The mechanism of intestinal
absorption is completely different for inorganic and
Se-met; therefore, factors that reduce absorption
of inorganic Se are unlikely to influence absorption
of Se-met. The metabolism of inorganic Se and
Se-met within a cell also differs. Inorganic Se is
used almost exclusively in the synthesis of selenospecfic
enzymes; whereas, Se-met can be used in
the synthesis of those enzymes, but it can also be
incorporated into any protein that contains
methionine. Clinical data comparing health effects
of inorganic Se and Se-yeast are lacking, but cattle
fed Se-yeast have higher concentrations of Se in
whole blood (average = 20% more) and milk (90%)
and activity of glutathione peroxidase (16%) than
cattle fed inorganic Se. Feeding Se-yeast during late
gestation also greatly increases the Se concentration
in tissues of the newborn calf. Based on available
data, the bioactivity of Se from Se-yeast is probably
about 20% higher than inorganic Se, but that
difference could be greater when absorption of
inorganic Se is reduced because of antagonists.