β-Carotene Absorption and Cleavage in Rats Is Affected by the Vitamin A Concentration of the Diet

Abstract

The purpose of this study was to examine whether intestinal beta-carotene cleavage activity, measured with the dioxygenase assay, is affected by vitamin A intake and whether this in vitro activity is a determinant of beta-carotene cleavage in vivo, measured in lymph-cannulated rats. Six groups of 10-20 rats were fed a diet with a low, normal or high retinyl palmitate concentration (120 RE, 1200 RE and 12,000 RE per kg, respectively) for 14 to 18 wk, either supplemented or not with 50 mg beta-carotene/kg in the last 6 wk. Intestinal dioxygenase activity was 90% higher (P < 0.05) in the animals fed the unsupplemented low vitamin A diet than in the animals fed the unsupplemented high vitamin A diet, whereas in beta-carotene-supplemented rats intestinal dioxygenase activity was significantly lower than in unsupplemented rats. The molar ratio between retinyl esters and beta-carotene in lymph collected over 8 h after a single intestinal dose of beta-carotene (250 micrograms) to beta-carotene-unsupplemented rats fed the three levels of vitamin A was correlated with intestinal dioxygenase activity (r = 0.66, P = 0.003). Dioxygenase activity in the liver was not affected by the vitamin A concentration of the diet but was 70% higher in the beta-carotene-supplemented rats. Based on the difference in liver vitamin A contents between beta-carotene-supplemented and unsupplemented rats we estimated beta-carotene conversion factors of 9:1 for the rats fed the high vitamin A diet and 4:1 for the rats fed the normal and low vitamin A diets. Intestinal beta-carotene cleavage activity is higher in vitamin A-deficient rats than in rats with a high intake of either vitamin A or beta-carotene. The intestinal dioxygenase activity as measured in vitro is an adequate indicator of in vivo beta-carotene cleavage activity.

Increase in serum beta-carotene following dark green leafy vegetable supplementation in Mebendazole-treated school children in Bangladesh

“…A low vitamin A status appears to increase b-carotene cleavage (van Vliet et al, 1996;Villard & Bates, 1986). The largest increase (0.13 mmolal) was seen among Takyi's subjects, who also had the lowest baseline retinol.…”

Circulating levels of retinol, tocopherol and carotenoid in Nepali pregnant and postpartum women following long-term β-carotene and vitamin A supplementation

“…This may Retinol, tocopherol and carotenoid in Nepali women S Yamini et al not be surprising among controls, given the low intakes of vegetables, fruit and dietary fat (data not shown) that might be expected to enhance carotenoid absorption (Takyi, 1999). However, serum concentration of b-carotene was exceedingly low even among women routinely supplemented with b-carotene, perhaps re¯ecting combined effects of inef®cient absorption of a single, large weekly supplement, ef®cient bioconversion of absorbed b-carotene to retinol in vitamin A-de®cient individuals (van Vliet et al, 1996) or rapid utilization of absorbed and intact b-carotene for possible antioxidant (Allard et al, 1994) or other metabolic (Moriguchi et al, 1996;Prabhala et al, 1991) functions. Serum lycopene was very low in our women, as has been observed in Malawi (Lan et al, 1999).…”

Research Recommendations for Applying Vitamin A-Labelled Isotope Dilution Techniques to Improve Human Vitamin A Nutrition

“…Determine how vitamin A status and other population characteristics infl uence vitamin A absorption, distribution, and metabolism Less effi cient bioconversion of β-carotene to vitamin A has been observed in animal studies as vitamin A status increases [23,24]. More information is needed on how vitamin A status infl uences parameters, such as absorption, bioconversion, and catabolic rates.…”