ARS | Publication request: Beta-carotene conversion to vitamin A decreases as the dietary dose increases in humans

Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 7, 2010
Publication Date: March 17, 2010
Citation: Novotny Dura, J., Harrison, D.J., Pawlosky, R., Flanagan, V.P., Harrison, E.H., Kurilich, A.C. 2010. Beta-Carotene conversion to vitamin A decreases as the dietary dose increases in humans. Journal of Nutrition. 140(5):915-918.

Interpretive Summary: Vitamin A deficiency continues to impose a major health impact throughout much of the developing world. The negative consequences of vitamin A deficiency include impaired resistance to infection, xerophthalmia, blindness, and increased risk of mortality. The World Health Organization estimates that 190 million preschool-aged children and 19 million pregnant women suffer from vitamin A deficiency. Beta-carotene is the primary plant-based source of dietary vitamin A, thus a clear understanding of factors influencing its potential for utilization as vitamin A has important public health implications. We conducted a study with adult volunteers to determine how the body’s absorption of beta-carotene and its utilization as vitamin A is influenced by dose. Our findings demonstrate that efficiency of beta-carotene conversion to vitamin A in humans is reduced at increasing doses. These results explain why vitamin A toxicity is not observed in individuals consuming large amounts of beta-carotene. This is important information for future revisions of vitamin A equivalency values for beta-carotene.

Technical Abstract: It has been suggested that high doses of B-carotene limit its conversion to vitamin A, yet this effect has not been well established in humans. A feeding study was conducted in which volunteers consumed two doses of deuterium labeled B-carotene on two occasions, with B-carotene and vitamin A response assessed by plasma area under the concentration-time curve. Seven volunteers (4 men, 3 women) consumed each of two doses of B-carotene-d8 and provided serial blood samples for 37 days after each dose. B-Carotene doses were 20 mg and 40 mg. Plasma B-carotene-d8 was assessed by HPLC-MS. Plasma retinol-d4, which was derived from the B-carotene-d8, was evaluated by GC-MS after saponification to convert retinyl esters to retinol. Plasma area under the concentration-time curve for B-carotene-d8 increased 2-fold from the 20 mg dose to the 40 mg dose. Plasma area under the concentration-time curve for retinol-d4 increased 36% from the 20 mg dose to the 40 mg dose. These results establish that in humans B-carotene conversion to vitamin A decreases as the dietary dose increases.