2018-10-13 11:02
来源:
双语营养学
Vitamin A Vs. Beta-Carotene
维生素A与胡萝卜素
原文网址：https://www.livestrong.com/article/466232-vitamin-a-vs-beta-carotene/
原文作者：JOANNE MARIE
A vitamin that your cells and tissues use for many essential functions, vitamin A is found in ready-to-use form in animal-based foods, but your body can also convert beta-carotene from plant-derived foods into vitamin A when needed. Beta-carotene may also have other benefits, in addition to being a precursor for vitamin A.
维生素A是一种细胞和组织用于很多必需功能的维生素，以现成形式见于动物性食品中，但人体也可以在需要时将植物来源食品中的β胡萝卜素转化为维生素A。除了是维生素A的前体，β胡萝卜素还有其他好处。
The Basic Vitamin
基础维生素
Vitamin A is actually a group of related compounds, called retinoids, with retinol the most common form. It's a fat-soluble vitamin that your body stores in your liver, ready to use when needed. Vitamin A supports your immune system and bones and is part of a compound called rhodopsin that absorbs light in your retina to help you see clearly. It's also crucial during development because it's used to produce new cells. Vitamin A is often measured in international units, and the Institute of Medicine recommends a daily intake of 3,000 international units for men and 2,310 for women, with slightly more during pregnancy and about 4,000 international units during breast-feeding.
维生素A实际上是一组彼此相关的复合物，称为类视黄醇类物质，视黄醇是其中最常见的形式。它是一种脂溶性维生素，人体将其储存在肝脏，在需要时随时可用。维生素A支持人的免疫系统和骨骼，是名为视紫红质的复合物的组成部分，该复合物在视网膜中吸收光线，帮助人看得清楚。在发育中，它也很关键，因为它用于生成新细胞。维生素A通常用国际单位来衡量，美国医学研究院建议，男人每天摄入3000国际单位，女人每天摄入2310国际单位，怀孕期间稍多，在母乳喂养时每天摄入4000国际单位。
Its Precursor
维生素的前体
Beta-carotene is called a provitamin A carotenoid because your body can convert it to active vitamin A. Also stored in your liver, it's a plant pigment that confers an orange or yellow color on many foods. Although no recommended dietary allowance has been established for beta-carotene, the Office of Dietary Supplements suggests consuming five or more servings of fruits and vegetables daily, adding deep yellow or orange examples regularly. Because beta-carotene has a different bio-activity than vitamin A, recommended daily amounts of vitamin A are also given in micrograms of retinol activity equivalents, with 12 micrograms of beta-carotene equivalent to 1 microgram of vitamin A, or retinol. In this system, a man needs 900 micrograms of RAEs and a woman needs 700.
β胡萝卜素称为原维生素A类胡萝卜素，因为人体能将其转化成活性维生素A。它也能储存在肝脏内，是一种植物色素，在很多食物中呈现出橙色或黄色。尽管对于β胡萝卜素没有规定饮食推荐摄入量，但膳食补品办公室建议：每天吃至少5份水果和蔬菜，经常加入深黄色或橙色类蔬果。由于相比维生素A，β胡萝卜素有不同的生物活性，因此，维生素A的推荐每日摄入量也以视黄醇活性当量的微克数给出，12微克的β胡萝卜素相当于1微克维生素A或视黄醇。在此系统中，一个男人的推荐每日摄入量是900微克胡萝卜素，而一个女人的是700。
Antioxidant Beta-Carotene
抗氧化剂β胡萝卜素
In addition to acting as a vitamin A precursor, beta-carotene may have other significant benefits as a potent antioxidant. Antioxidants deactivate unstable chemicals called free radicals that form in your body during digestion, when you're exposed to sunlight or after you encounter toxins such as those in cigarette smoke. Over time, free radicals may raise your risk of heart disease, cancer and other disorders. Laboratory research summarized by experts at Memorial Sloan-Kettering Cancer Center suggests beta-carotene may slow growth of cancer cells while boosting immune cells that destroy cancer. Results of clinical trials with beta-carotene, however, are either conflicting or inconclusive, so more study into its effects on human subjects is needed.
除了充当维生素A前体，作为强力抗氧化剂，β胡萝卜素可能还有其他重要的好处。人在消化时，暴露在日晒下，或者吸入烟草雾气等毒素后，体内就会形成称为自由基的不稳定化学物质，而抗氧化剂可抑制其活化。不然，时间一长，自由基就会提高人患心脏病、癌症及其他疾病的风险。纪念斯隆-凯特琳癌症中心的专家们总结的实验室研究表明：β胡萝卜素可减缓癌细胞增长，同时增强摧毁癌症的免疫细胞活性。然而，对β胡萝卜素的临床试验要么彼此冲突，要么没有明确的结论，因此，对人体受试者的效果，还需要更多的研究。
Sources and Concerns
来源和要注意的问题
Foods rich in vitamin A include beef liver, fish, eggs, poultry and dairy products, as well as cereals and baked goods fortified with vitamin A. Beta-carotene is provided by many fruits and vegetables, with sweet potatoes, spinach, carrots, cantaloupe and mangoes being especially rich. Most multivitamin tablets contain vitamin A, and vitamin A-only supplements are also available, although the Office of Dietary Supplements says that eating a wide range of foods is the best way to ensure you consume enough vitamin A. Because your body can store the vitamin, taking too much vitamin A has some health risks and may lead to symptoms that include neurological problems and joint pain. High intake of beta-carotene doesn't carry the same risk because it's converted only as needed.
富含维生素A的食物有牛肝、鱼、鸡蛋、禽类和乳制品等，还有维生素A强化的谷物和烘焙产品。很多水果和蔬菜都提供β胡萝卜素，红薯、菠菜、胡萝卜、哈密瓜和芒果含量尤其丰富。大部分多维药片都含有维生素A，纯维生素A补品也能买到，不过，膳食补品办公室说：吃丰富多彩的食物，是确保摄入充足维生素A的最佳途径。因为人体会储存维生素，所以，摄入过多维生素A有些健康风险，可能会导致神经问题和关节疼痛等症状。大量摄入β胡萝卜素不会带来同样风险，因为它只在需要时才转化为维生素A。返回搜狐，查看更多
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