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ARS Home » Northeast Area » Boston, Massachusetts » Jean Mayer Human Nutrition Research Center On Aging » Research » Publications at this Location » Publication #135945
Title: SHORT-TERM (INTESTINAL) AND LONG-TERM (WHOLE BODY) CONVERSION OF BETA-CAROTENE TO VITAMIN A IN ADULTS USING A STABLE ISOTOP REFERENCE METHOD

Author
item TANG, GUANGWEN - HNRCA
item QIN, JIAN - HNRCA
item DOLNIKOWSKI, GREGORY - HNRCA
item RUSSELL, ROBERT - HNRCA

Submitted to: The American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2003
Publication Date: 8/1/2003
Citation: TANG, G., QIN, J., DOLNIKOWSKI, G.G., RUSSELL, R.M. SHORT-TERM (INTESTINAL) AND LONG-TERM (WHOLE BODY) CONVERSION OF BETA-CAROTENE TO VITAMIN A IN ADULTS USING A STABLE ISOTOP REFERENCE METHOD. AMERICAN JOURNAL OF CLINICAL NUTRITION. 2003;78:259-66.

Interpretive Summary: Beta Carotene is a compound in food which is able to be converted to Vitamin A. However, the efficiency of conversion of beta-carotene is variable, and has not been accurately quantified. An amount of pure beta carotene which could normally be found in a meal that is rich in fruits and vegetables (6 mg) was given to 22 adult volunteers (10 males and 12 females). The beta carotene had been especially labeled, so that the efficiency of its breakdown in the body to vitamin A could be exactly determined. In addition, a reference dose of pure vitamin A (labeled differently) was given. Blood samples were then collected over 56 days. The average conversion of beta carotene to vitamin A was 9 to 1 - that is, it would take 9mg of pure beta carotene to convert to 1 mg of vitamin A. It was also determined that 84% of the conversion takes place in the intestine, while 16% of the conversion takes place in other organs of the body. Persons who are obese converted beta- carotene less efficiently.

Technical Abstract: Quantitative and detailed information on the conversion of beta-carotene (b-C) to vitamin A in humans is limited. Our objective is to determine the short and long term conversion of synthetic deuterium labeled b-C to vitamin A in well-nourished adults by using a stable isotope reference method. A physiological dose of D8 b-C (11,011 nmole or 6 mg) in oil was given with a liquid diet (25 % energy from fat) to 22 adult volunteers (10 males and 12 females). Three days after the D8 b-C dose, the volunteers each took a reference dose of D8 retinyl acetate (8,915 nmole or 3 mg) in oil with the same liquid diet. Blood samples were collected over 56 d. B-C and retinol were extracted from serum and isolated by high performance liquid chromatography. The serum retinol and b-C enrichments were respectively determined by using gas chromatograph/mass spectrometry with electron capture negative chemical ionization and liquid chromatograph /mass spectrometry with an atmospheric pressure chemical ionization interface. The 53 d area under the serum D4 retinol response curve (from the D8 b-C dose) was 569.0 ± 385.3 nmole-d and the 53 d area under the serum D8 retinol response curve (from the D8 retinyl acetate dose) was 1797.9 ± 1139.1 nmole-d. By using D8 retinyl acetate as the vitamin A reference, the D4 retinol formed from D8 b-C (11,011 nmole) was calculated to be equivalent to 3413.59 ± 2298.4 nmole of retinol. The conversion factor of b-C to retinol varied from 2.4 to 20.2, and the average conversion factor was 9.0 to 1 on a weight basis or 4.8 to 1 on a molar basis. This conversion factor was positively correlated with BMI (r = 0.6, p < 0.005). The post absorption conversion of b-C was estimated as 4.8, 9.6, 12.1, and 16.1 % of the total converted retinol at 6-, 14-, 21-, 53-d after the D8 b-C dose, respectively. The quantitative determination of the conversion of b-C to vitamin A in humans can be accomplished by using a stable isotope reference method. This approach provides in vivo metabolic information after a physiological dose of b-C.