Selenium absorption and retention from a selenite- or selenate-fortified milk-based formula in men measured by a stable-isotope technique

The present study was designed to determine the apparent absorption and retention of the inorganic Se compounds SeO₃^2- and SeO₄^2-, which are commonly used for Se fortification of clinical nutrition products and infant formulas. Ten healthy men were fed a milk-based formula labelled with 40 μg Se as ⁷⁴SeO₃^2- or ⁷⁶SeO₄^2- on two consecutive days using a randomised crossover design. Se stable-isotope analysis of 9 d complete collections of urine and faeces was used to calculate apparent Se absorption and retention. Se retention from ⁷⁴SeO₃^2- (41.0 (SD 8.4) %) and from ⁷⁶SeO₄^2- (46.0 (SD 7.9) %) was not significantly different (P > 0.05). However, Se absorption was significantly higher from SeO₄^2- than from SeO₃^2- (91.3 (SD 1.4) % v. 50.2 (SD 7.8) %, P < 0.05). Urinary excretion of the administered dose was 9.2 (SD 1.8) % for ⁷⁴SeO₃^2- and 45.3 (SD 8.2) % for ⁷⁶SeO₄^2- (P < 0.05). Urinary Se excretion kinetics differed significantly for the two Se compounds; 90 % of the total urinary Se was excreted after 121 h for ⁷⁴SeO₃^2- and after 40 h for ⁷⁶SeO₄^2- (P < 0.05). These results suggest that although Se absorption and urinary excretion differ for SeO₃^2- and SeO₄^2-, both Se compounds are equally well retained when administered at a relatively low dose (40 μg Se). The nutritional impact of Se fortification of foods would thus be expected to be similar when SeO₄^2- or SeO₃^2- are used.