Submitted to: Journal of Lipid Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/10/2005
Publication Date: 5/16/2005
Citation: Novotny Dura, J., Kurilich, A.C., Britz, S.J., Clevidence, B.A. 2005. Plasma appearance of labeled beta-carotene, lutein, and retinol in human consumption of iso topically-labeled kale. Available online: http://pubs.acs.org/cgi-bin/asap.cgi/jafcau/asap/html/jf050570o.html. Interpretive Summary: Carotenoids are compounds that provide health-promoting effects of fruits and vegetables. Kale is rich in two key carotenoids: lutein and beta-carotene. Beta-carotene can form vitamin A, thus it is critical for battling vitamin A deficiency, the most widespread and serious nutritional deficiency in the world. Lutein is the main nutritional component associated with decreasing risk of macular degeneration, the most common age-related cause of blindness. To study the body's ability to absorb these carotenoids from kale, we added tags (called isotopes) to the nutrients within the vegetable itself. The tags allow us to monitor the absorption of the nutrient into the body, since the tags prevent the nutrients from becoming lost in the body's pool of existing nutrient. This pioneering method has revealed many new findings. Our results show that lutein is absorbed much better than beta-carotene. And even given this disparity, we have demonstrated that the best lutein absorbers are the best beta-carotene absorbers, suggesting some similarities in absorption (a poorly understood process). We have also shown the formation of tagged vitamin A from the tagged beta-carotene, helping to address the very controversial question of how well plant foods can provide vitamin A. These results provide extremely useful information for determination of dietary intake recommendations by health experts. These results provide solid evidence to health professionals and policy makers for the ability of vegetable-based beta-carotene to provide vitamin A to needy populations. And these data provide scientists with important correlations for understanding how these important compounds are absorbed.
Technical Abstract: The bioavailability of carotenoids from kale was investigated by labeling the nutrients in the kale with carbon-13, feeding the kale to 7 adults, and analyzing serial plasma samples for labeled lutein, beta-carotene, and retinol. Peak plasma concentrations, area under the plasma concentration-time curves (AUC), enrichments of the endogenous plasma pools, and percents of dose recovered at peak plasma concentrations were calculated. Average peak plasma concentrations for the 7 subjects were 0.38, 0.068, and 0.079 micromolar for labeled lutein, beta-carotene, and retinol, respectively. Average AUC values were 42.8, 13.6, 13.2 micromolar-hr for labeled lutein, beta-carotene, and retinol, respectively. Percent enrichments of endogenous plasma pools were 121%, 30%, and 2.7% for labeled lutein, beta-carotene, and retinol, respectively. Percents of dose recovered at peak plasma concentrations were 3.6%, 0.7%, and 0.7% for labeled lutein, beta-carotene, and retinol, respectively. Positive correlations were found between factors representing lutein and beta-carotene absorption as well as between beta-carotene and retinol plasma response. It was concluded that lutein is substantially more bioavailable from kale than beta-carotene. In addition, a positive correlation between lutein AUC and the sum of AUCs for beta-carotene and retinol supports the existence of common features of absorption between lutein and beta-carotene.