|Muzhingi, Tawanda -|
|Gadaga, Tendekayi -|
|Siwela, Andrew -|
Submitted to: American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 24, 2011
Publication Date: August 1, 2011
Citation: Muzhingi, T., Gadaga, T.H., Siwela, A.H., Grusak, M.A., Russell, R.M., Tang, G. 2011. Yellow maize with high beta-carotene is an effective source of vitamin A in healthy Zimbabwean men. American Journal of Clinical Nutrition. 94(2):510-519. Interpretive Summary: The food crop known as maize (or corn) contains a number of health-promoting compounds in its grains, including substances that impart color, such as the yellow-orange pigment, beta-carotene. Different maize varieties contain different amounts of these colored compounds, but cultivars exist that have a high concentration of grain beta-carotene. We used one such variety to study how well this beta-carotene can be absorbed and converted to vitamin A in humans. Beta-carotene is found in many plant foods and serves as a dietary precursor of vitamin A. We grew the maize plants in a nutrient solution with a special form of water; this water contained a heavy form of hydrogen. This allowed us to label the beta-carotene in the maize grains so that after feeding the maize to study subjects, we could track not only the beta-carotene in their blood, but also the vitamin A derived from that beta-carotene. In a study with eight healthy men from Zimbabwe, we showed that beta-carotene from cooked maize porridge is well absorbed and readily converted to vitamin A. Thus, yellow maize that contains beta-carotene can contribute to one's daily requirement of vitamin A.
Technical Abstract: The bioconversion efficiency of yellow maize beta-carotene to retinol in humans is unknown. Thus, the objective of this study was to determine the vitamin A value of yellow maize beta-carotene in humans. A high beta-carotene containing yellow maize was grown in a hydroponic medium with 23 atom% 2H2O during grain development. Yellow maize beta-carotene showed the highest abundance of enrichment as [2H9] beta-carotene. Eight healthy Zimbabwean men with a mean serum retinol concentration of 59.2 +/- 17.l ug/dL, and mean body mass index (in kg/m2) of 22.4 +/- 3.1 volunteered for the study. On day 1 after a fasting blood draw, subjects consumed 300 g of yellow maize porridge containing 1.2 mg beta-carotene, 20 g of butter, and a 0.5 g corn oil capsule. On day 8, fasting blood was drawn and subjects consumed 1 mg [13C10] vitamin A in 0.5 g corn oil capsule, and 300 g of white maize porridge with 20 g of butter. Thirty-six blood samples were collected from each subject over 36-days. Concentrations and enrichments of retinol and beta-carotene in labeled doses, and serum were determined using HPLC, GC/MS, and LC/MS. The AUC of retinol from 1.2 mg yellow maize beta-carotene was 72.9 nmole/day and the AUC of 1 mg retinol 13C10 was 161.1 nmole/day. The conversion factor of yellow maize beta-carotene to retinol by weight was 3.2 +/- 1.5 to 1. Thus, in eight healthy Zimbabwean men, 1.2 mg yellow maize beta-carotene consumed with 20.5 g fat has the same vitamin A activity as 0.38 mg retinol.