Uncertainty Assessment. An uncertainty factor (UF) of 2 was selected to protect sensitive individuals. The toxic effect is not severe, but may not be readily reversible, so a UF greater than 1 is needed.

Derivation of a UL. The NOAEL of 800 µg/day was divided by a UF of 2 to obtain a UL for adults as follows:

Brätter et al. (1996) studied the effects of selenium intake on metabolism of thyroid hormones in lactating mothers in seleniferous regions in the foothills of the Venezuelan Andes. Selenium intakes ranged from 170 to 980 µg (2.2 to 12.4 µmol)/day. An inverse correlation between selenium intake and free triiodothyronine (FT₃) was observed, but all values were found to be within the normal range.

There are no reports of teratogenicity or selenosis in infants born to mothers with high but not toxic intakes of selenium. Therefore, ULs for pregnant and lactating women are the same as for nonpregnant and nonlactating women (400 µg [5.1 µmol]/day).

Data Selection. There are several approaches for estimating a UL in human milk-fed infants (Levander, 1989). However, the most conservative approach is to use the data of Shearer and Hadjimarkos (1975).