Bioavailability and bioefficacy of [beta]-carotene measured using 13C-labeled [beta]-carotene and retinol: studies in Indonesian children

Vitamin A deficiency is a serious health problem in many developing countries. Improved vitamin A status can reduce morbidity and mortality by one-third in developing countries. Vitamin A occurs in food as preformed vitamin A (retinol), present in animal foods and breastmilk, and as provitamin A carotenoids - the major source of vitamin A for a large proportion of the world's population. However, the contribution of plant foods can only be substantial when not only the consumption and provitamin A content of foods but also the bioefficacy of provitamin A carotenoids in such foods is high. With respect to provitamin A carotenoids, bioefficacy is the product of the fraction of the ingested amount which is absorbed (bioavailability) and the fraction of that which is converted to retinol in the body (bioconversion). Isotopic tracer techniques can supply accurate and precise data on bioavailability, bioconversion and bioefficacy of carotenoids in humans.A new stable isotope technique - based on reaching plateau isotopic enrichment ofβ-carotene and retinol in serum during prolonged intake of multiple low doses ofβ-carotene and retinol, each specifically labeled with 10 13C atoms - has been developed. In 2 studies, for periods≤10 wk, > 100 Indonesian children (aged 7-13 y), consumed daily 2-3 doses of specifically labeled [ 13C 10 ]β-carotene (≤80μg/dose) and [ 13C 10 ]retinyl palmitate (≤90μg/dose). In the second study, half of the subjects ( n = 41) also received spinach while the others ( n = 36) received pumpkin. Either in serum or in feces, the degree of isotopic enrichment of retinol with [ 13C 5 ]retinol - derived from administered [ 13C 10 ]β-carotene - and with [ 13C 10 ]retinol, and ofβ-carotene with [ 13C 10 ]β-carotene was measured by high performance liquid chromatography with atmospheric pressure chemical ionization liquid chromatography-mass spectrometry (APCI LC-MS). These techniques have emerged as the most effective and convenient for studying the bioavailability, bioconversion and bioefficacy of provitamin A carotenoids. For interpretation of data, a mathematical model has been developed based on assumptions that can be readily justified in the light of present knowledge on carotenoid metabolism.From the studies presented, it can be concluded that 2.6μgβ-carotene in oil has the same vitamin A activity as 1μg retinol (bioefficacy ofβ-carotene in oil, 36%). The bioavailability ofβ-carotene in oil was found to be 86%. The bioavailability and bioefficacy ofβ-carotene in pumpkin ranged from 1.7 to 1.8 times those ofβ-carotene in spinach. Results obtained using data from feces confirmed results obtained using data from serum.This plateau isotopic enrichment technique can be applied for studying the effect of individual SLAMENGHI factors which affect the bioavailability and bioefficacy of carotenoids in humans (SLAMENGHI is a mnemonic for such factors). The studies presented have provided the most reliable estimates of the bioefficacy ofβ-carotene in oil available to date. The estimates are most probably applicable to children in other developing countries. Results from recent studies and from those presented in this thesis indicate that the current guidelines that the vitamin A activity of 1μ>g retinol can be supplied by 6μg (FAO/WHO) and 12μg (US Institute of Medicine) ofβ-carotene in a mixed diet overestimateβ-carotene bioefficacy about 2 to 3 times. This means that approaches other than the promotion of fruit and vegetables are required for eliminating vitamin A deficiency.