This Kinetic, Bioavailability, and Metabolism Study of RRR-α-Tocopherol in Healthy Adults Suggests Lower Intake Requirements than Previous Estimates^1,2

Abstract

Kinetic models enable nutrient needs and kinetic behaviors to be quantified and provide mechanistic insights into metabolism. Therefore, we modeled and quantified the kinetics, bioavailability, and metabolism of RRR-α-tocopherol in 12 healthy adults. Six men and 6 women, aged 27 ± 6 y, each ingested 1.81 nmol of [5^-14CH₃]-(2R, 4'R, 8'R)-α-tocopherol; each dose had 3.70 kBq of¹⁴C. Complete collections of urine and feces were made over the first 21 d from dosing. Serial blood samples were drawn over the first 70 d from dosing. All specimens were analyzed for RRR-α-tocopherol. Specimens were also analyzed for ¹⁴C using accelerator MS. From these data, we modeled and quantified the kinetics of RRR-α-tocopherol in vivo in humans. The model had 11 compartments, 3 delay compartments, and reservoirs for urine and feces. Bioavailability of RRR-α-tocopherol was 81 ± 1%. The model estimated residence time and half-life of the slowest turning-over compartment of α-tocopherol (adipose tissue) at 499 ± 702 d and 184 ± 48 d, respectively. The total body store of RRR-α-tocopherol was 25,900 ± 6=220αmol (11 ± 3 g) and we calculated the adipose tissue level to be 1.53 αmol/g (657αg/g). We found that a daily intake of 9.2αmol (4 mg) of RRR-α-tocopherol maintained plasmaRRR-a-tocopherol concentrations at 23αmol/L. These findings suggest that the dietary requirement for vitamin E may be less than that currently recommended and these results will be important for future updates of intake recommendations.