Influence of dietary spices on the in vivo absorption of ingested β-carotene in experimental rats.

Animal studies were conducted to evaluate the influence of dietary spice compounds, piperine, capsaicin and ginger, on the absorption of orally administered β-carotene and its conversion to vitamin A. In rats maintained on these spice-containing diets for 8 weeks, concentrations of β-carotene and retinol were determined in the serum, liver and intestine 4 h after a single oral administration of β-carotene. β-Carotene concentration was significantly increased in the serum, liver and intestine of piperine- and ginger-fed rats, suggesting improved absorption of β-carotene. However, retinol concentration was not significantly changed in these animals, suggesting that the bioconversion of β-carotene to vitamin A was not similarly influenced. Between the two enzymes involved in the bioconversion of β-carotene to vitamin A, the activity of intestinal and hepatic β-carotene 15,15'-dioxygenase was either unaffected or lowered by these spice treatments. The activity of intestinal and hepatic retinal reductase was unaffected by the dietary spices. Activities of these two enzymes involved in the bioconversion of β-carotene to retinal were inhibited by the test spices in vitro, thus corroborating with the in vivo observation. Although the bioconversion of β-carotene was not promoted, increased absorption and tissue levels of β-carotene by the dietary spices may contribute to a higher antioxidant protection.