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Variability in conversion of β-carotene to vitamin A in men as measured by using a double-tracer study design
- Hickenbottom, S.J., Follett, J.R., Lin, Y., Dueker, S.R., Burri, B.J., Neidlinger, T.R., Clifford, A.J.
- American journal of clinical nutrition 2002 v.75 no.5 pp. 900
- beta-carotene, retinyl acetate, nutrition physiology, metabolism, vitamin A, isotope labeling, deuterium, blood plasma, men
- Background: The vitamin A activity of β-carotene is variable and surprisingly low in women. The reasons for this are not well understood. The vitamin A activity of β-carotene in men is still uncertain. Contributions of dietary factors compared with individual traits are largely unknown. Objective: Our objective was to measure the intrinsic variability in the vitamin A activity of β-carotene among healthy, well-fed men living in a controlled environment. Design: We used a double-tracer test-retest design. We dosed 11 healthy men orally with 30 μmol hexadeuterated (D6) retinyl acetate (all-trans-19,19,19,20,20,20-[2H6]retinyl acetate) and then with 37 μmol D6 β-carotene (19,19,19,19',19',19'-[2H6]β-carotene) 1 wk later. Doses were taken with breakfasts containing 16 g fat. We measured D6 retinol, D6 β-carotene, and trideuterated (D3) retinol (derived from D6 β-carotene) concentrations in plasma. Areas under the plasma concentration x time since dosing curves (AUCs) were determined for D6 retinol, D6 β-carotene, and D3 retinol. Results: All men had detectable D6 retinol concentrations in plasma. The mean (±SE) absorption of D6 β-carotene in all subjects was 2.235 ± 0.925%, and the mean conversion ratio was 0.0296 ± 0.0108 mol retinol to 1 mol β-carotene. Only 6 of 11 men had sufficient plasma concentrations of D6 β-carotene and D3 retinol that we could measure. The mean absorption of D6 β-carotene in these 6 subjects was 4.097 ± 1.208%, and the mean conversion ratio was 0.0540 ± 0.0128 mol retinol to 1 mol β-carotene. Conclusion: The vitamin A activity of β-carotene, even when measured under controlled conditions, can be surprisingly low and variable.