Previous metabolic studies of
selenium used pure
selenium compounds with pharmacologic activities unrelated to
selenium nutrition. Healthy men were fed foods naturally high or low in
selenium while confined to a metabolic research unit.
Selenium intake was 47 microg/
d (595 nmol/d) for 21 d while energy intakes and
body weights were stabilized and
selenium excretion and intake came into metabolic balance. On d 22,
selenium intake was changed to either 14 microg/d (177 nmol/d, low
selenium) or 297 microg/d (3.8 micromol, high
selenium) for the remaining 99 d. The absorption, distribution and excretion of
selenium in food were similar to
selenomethionine, and distinctly different from
sodium selenite. Daily urinary
selenium excretion and
selenium concentrations in plasma and RBC showed the largest responses to
selenium intake relative to interindividual variation. Urinary
selenium and plasma
selenium responded most rapidly to changes in
selenium intake, whereas RBC reflected longer-term
selenium intake. Given the difficulty of 24-h urine collections outside a metabolic research unit, RBC and plasma
selenium seem to be the most useful indicators of
selenium intake. During the intervention period, the high
selenium group retained 15 mg (190 micromol) of
selenium, with approximately 5 mg (63 micromol) going into skeletal muscle. The low
selenium group lost only 0.9 mg (11 micromol) of whole-body
selenium but lost 3.3 mg (42 micromol) from muscle, indicating that
selenium was redistributed from muscle to tissues that have a higher metabolic priority for
selenium such as testes. Fecal excretion decreased by half, representing an important but previously underappreciated adaptation to
selenium restriction.