From Beta-carotene to Vitamin A

Vitamin A deficiency is a serious nutritional problem in the developing world particularly in areas where the diet is predominantly plant-based. Since preformed active vitamin A is only found in foods of animal origin, vitamin A deficiency may also be a problem for strict vegetarians unless they are making a conscious effort to consume vegetables and fruits that contain significant amounts of the vitamin A precursor, beta-carotene.

Checking the root structure of labeled collards  

Many foods from plants contain beta-carotene. Foods that are bright orange or deep green, such as carrots and spinach, are the best sources of beta-carotene. Unfortunately, little is known about how beta-carotene is absorbed in the body or how much of the vegetable derived beta-carotene from most foods is converted to vitamin A (also known as that food’s vitamin A activity).

Dr. Michael Grusak and his colleagues at the USDA/ARS Children’s Nutrition Research Center use a stable isotope method to tag beta-carotene in vegetables, so that it can be traced when fed to human subjects. In collaboration with USDA researchers at Tufts University, this approach is used to determine how much beta-carotene is absorbed from each food and how efficiently it is converted to vitamin A. Currently, the Food and Nutrition Board of the Institute of Medicine (IOM) uses a beta-carotene to vitamin A conversion factor of 12 to 1. In other words, a food that contains 12 mg of beta-carotene equivalents is believed to provide 1 mg of vitamin A to the body.

The IOM conversion value is an average and does not represent the actual conversion efficiency of different foods or of foods under varying conditions. For example, processing can promote the release of beta-carotene from foods. Dietary fat or oils tend to increase absorption. Dr Grusak adds,

“There is no doubt that highly colored fruits and vegetables are important sources for alleviating vitamin A deficiency in at-risk families. This is one reason that nutritionists encourage their intake. However, if more information was available on the vitamin A activity of specific plant foods and their use in diverse population groups, targeted recommendations could be made to the general public and the health-related community.” The CNRC researchers are anxious to learn about novel beta-carotene rich foods and welcome any information about new foods that deserve further attention. Additional information about beta-carotene conversion to vitamin A has been published in the Trees for Life Journal and is available at www.tfljournal.org/article.php/20051201123813474.