Abstract
Carotenoid pigments comprise a large and interesting group of compounds that first caught the attention of chemists because of their deep yellow, orange, and red colors. They represented some of the first compounds that were separated by chromatography, and to this day, that is an important analytical technique for both quantitating and characterizing carotenoids. Then in 1930, it became apparent that some of the carotenoids could replace vitamin A in animal diets, and this was followed by the realization that some carotenoids were metabolic precursors of vitamin A (1). The ability to function as a provitamin A was limited to those carotenoids with an unsubstituted β-ionone group, and included β-carotene, α-carotene, β-cryptoxanthin, and several others that are very poorly represented in the human diet. Examples of the provitamin A and nonprovitamin A carotenoids found in human plasma are depicted in Figure 1. Carotenoids such as lycopene, the major pigment of tomatoes, or astaxanthin, the major pigment of crustaceans, do not have the requisite structure and therefore, are not provitamin A carotenoids.
For about 50 years, the nutritional and health interest in carotenoids was limited to the provitamin A pigments. However, this changed when epidemiologists, investigating the relationship between diets and disease, found a relationship between diets rich in green leafy vegetables and red, orange, and yellow fruits and vegetables and a decreased risk of developing various types of cancer and other chronic diseases. At first, this effect was attributed to the vitamin A value of these diets, but a closer analysis of the early data indicated that food tables had converted the content of provitamin A carotenoids into vitamin A values. Soon investigators began focusing on the carotenoid content of diets and their relationship to disease. This efforst was greatly stimulated by the 1981 article entitled “Can Dietary β-Carotene Materially Reduce Human Cancer Rates?” by Peto et al. (2). Since then, there have been many articles published supporting the idea that diets rich in fruits and green vegetables reduce chronic disease risk, and other investigations have found the same relationship between plasma levels of carotenoids and decreased risk of disease (3, 4).
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