Submitted to: American Journal of Clinical Nutrition
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/13/2002
Publication Date: 7/13/2002
Citation: Hickenbottom, S.J., Follet, J.R., Lin, Y., Dueker, S.R., Burri, B.J., Neidlinger, T.R., Clifford, A.J. 2002. Variability in conversion of b-carotene to vitamin a in men as measured by using a double-tracer study design. American Journal of Clinical Nutrition. American Journal of Clinical Nutrition. 75:900-907. Interpretive Summary: Vitamin A deficiency is the most common cause of nutritional blindness in the world, and a leading cause of death in young children. Fruits and vegetables containing beta-carotene (such as carrots, mangos, and sweet potatoes) are the major sources of vitamin A for all people who cannot afford or do not wish to eat large amounts of meat and milk. However, results from studies that have tried to correct vitamin A deficiency with beta-carotene rich fruits and vegetables have been disappointing. There are many reasons why these programs have been disappointing; including the possibilities that they were given to children who were already sick, or that they used the wrong type of vegetables. We measured how well pure beta-carotene is converted to vitamin A in healthy men using advanced scientific techniques. We found that even when we fed beta-carotene to healthy adult men under ideal conditions, beta-carotene absorption was poor and variable. Once beta-carotene was absorbed,it converted to vitamin A well. So, these experiments proved that beta-carotene absorption is the problem (instead of its metabolism). They also showed that beta-carotene absorption is poor and variable even under ideal conditions, which is an important finding that will be used in public health programs that seek to correct vitamin A deficiency.
Technical Abstract: The vitamin A activity of B-carotene is variable and surprisingly low in women. The reasons for this are not well understood. The vitamin A activity of B-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 variablility in the vitamin A activity of B-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 umol hexadeuterated (D6) retinylacetate(all-trans-19, 19,19,19,20,20,20-[2H6]retinyl acetate) and then with 37 umol D6 B-carotene (19,19,19,19',19',19'-[2H6]B-carotene) 1 wk later. Doses were taken with breakfasts containing 16g fat. We measured D6 retinol, D6 B-carotene, and trideuterated (D3)retinol (derived from D6 B-carotene) concentration in plasma. Areas under the plasma concentration X time since dosing curves (AUCs) were determined for D6 B-carotene, and D3 retinol. Results: All men had detectable D6 retinol concentrations in plasma. The mean (+SE) absorption of D6 B-carotene in all subjects was 2.235, and the mean conversion ratio was 0.0296+0.0108 mol retinol to 1 mol B-carotene. Only 6 of 11 men had sufficient plasma concentrations of D6 B-carotene and D3 retino that we could measure. The mean absorption of D6 B-carotene in these 6 subjects was 4.097 + 1.208%, and the mean conversion ratio was 0.0540+0.0128 mol retional to 1 mol B-carotene. Conclusion: The vitamin A activity of B-carotene, even when masured under controlled conditions, can be surprisingly low and variable.