Submitted to: Proceedings of the National Academy of Sciences
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/10/2007
Publication Date: 2/1/2008
Publication URL: www.pnas.org/cgi/reprint/105/5/1431
Citation: Morris, J., Hawthorne, K.M., Hotze, T., Abrams, S.A., Hirschi, K.D. 2008. Nutritional impact of elevated calcium transport activity in carrots. Proceedings of the National Academy of Sciences. 105(5):1431-1435. Interpretive Summary: Osteoporosis is one of the world's most prevalent nutritional disorders ,and inadequate dietary calcium is a known contributor to this condition. By genetically altering vegetables to increase calcium levels, we can boost calcium uptake and reduce the incidence of calcium insufficiency. We demonstrate here a novel way of making vegetables with increased levels of bioavailable calcium. This work directly evaluates the nutritional consequence of transgenic foods in human feeding studies. We established that modifying a single plant calcium transporter improves plant calcium absorption in humans. Additionally, the approach in this work can serve as a model for related studies regarding how changes in the plant alter bioavailability of nutrients.
Technical Abstract: Nutrition recommendations worldwide emphasize ingestion of plant-based diets rather than diets that rely primarily on animal products. However, this plant-based diet could limit the intake of essential nutrients such as calcium. Osteoporosis is one of the world's most prevalent nutritional disorders, and inadequate dietary calcium is a known contributor to the pathophysiology of this condition. Previously, we have modified carrots to express increased levels of a plant calcium transporter (sCAX1), and these plants contain approximately 2-fold higher calcium content in the edible portions of the carrots. However, it was unproven whether this change would increase the total amount of bioavailable calcium. In randomized trials, we labeled these modified carrots with isotopic calcium and fed them to mice and humans to assess calcium bioavailability. In mice feeding regimes (n = 120), we measured (45)Ca incorporation into bones and determined that mice required twice the serving size of control carrots to obtain the calcium found in sCAX1 carrots. We used a dual-stable isotope method with (42)Ca-labeled carrots and i.v. (46)Ca to determine the absorption of calcium from these carrots in humans. In a cross-over study of 15 male and 15 female adults, we found that when people were fed sCAX1 and control carrots, total calcium absorption per 100 g of carrots was 41% +/- 2% higher in sCAX1 carrots. Both the mice and human feeding studies demonstrate increased calcium absorption from sCAX1-expressing carrots compared with controls. These results demonstrate an alternative means of fortifying vegetables with bioavailable calcium.