Factors influencing the uptake and absorption of carotenoids

In his classic book entitled Vitamin A, Thomas Moore wrote, “There are many complicating factors, both chemical and physiological, which will make it difficult to give an account of the absorption of vitamin A and its provitamins (carotenoids) which is both clear and reasonably comprehensive (1).” Although this statement accurately depicts our current ability to describe carotenoid absorption, it was written in 1957. In the last four decades, thousands of papers have been written about carotenoids, yet many questions still remain unanswered regarding the absorption of both provitamin A active carotenoids such as α-and β-carotene (BC), and carotenoids such as lycopene that do not have vitamin A activity. Carotenoids are a family of over 600 fat-soluble pigments. The two subclasses of carotenoids are the oxygenated xanthophylls and the hydrocarbon carotenes. In nature, carotenoids are responsible for some of the characteristic colors in fall leaves, birds, fruits, vegetables, and shellfish. For example, tomatoes are red and carrots are orange primarily because of lycopene and β-carotene, respectively. Lutein, BC, and lycopene, shown in Figure 1, are the predominant carotenoids in our diet, serum, and tissues. Emerging evidence that lycopene may have a role in reducing risk of both prostate cancer (2) and myocardial infarction (3) has rekindled interest in the factors that influence its absorption. Most of the research investigating carotenoid absorption has utilized BC as a model carotenoid, assuming that all carotenoids behave similarly during digestion. For the most part, this is probably true. However, the degree of influence a particular factor has may vary with the structural characteristics of each carotenoid. Because BC and lycopene are both hydrocarbon carotenes, it is expected that modification of dietary conditions affects each in a similar manner. The reviews by Erdman et al., Wang, and Parker are recommended for further detail on the factors that affect BC absorption (4–6).