A vitamin precursor that the body converts to its active form through normal metabolic processes. Carotene for example is a provitamin of vitamin a.

维生素原一种由身体通过正常新陈代谢过程，将其转化成活跃形式的维生素的前体，比如，胡萝卜素是维生素a的维生素原。

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Folic acid is a precursor of folate, a vitamin found in foods such as spinach and oranges.

叶酸是维生素b的前体，存在于菠菜、柑橘等食物中。

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Coffee is a major source of the phenolic compound chlorogenic acid and the vitamin B3 precursor trigonelline that have been shown to reduce blood glucose concentrations in animal studies.

咖啡是酚类成份绿原酸以及维他命b 3前驱物胡卢巴碱的重要来源，胡卢巴碱在动物研究中显示可降低血糖浓度。

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Supplements of beta-carotene, which is a precursor of the antioxidant vitamin A, should be used with caution, however.

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