Carotenoids are a group of over 600 compounds, excluding isomers, which are biosynthesized by plants and microorganisms but not animals. They are involved in the photosynthesis process, in conversion to vitamin A and in plant leaf abscission. Furthermore, they form the color components of many plants (including flowers) and animals and especially birds. All of the carotenoids have a similar chemical structure and the vast majority of the active forms in the human cell are the trans configuration molecules.
1. A central function of carotenoids is as a precursor to vitamin A although, of the major dietary carotenoids, b-carotene and -carotene are the only types where the conversion is significant. The conversion rate for b-carotene is that 6µg of b-carotene provide 1µg of retinal equivalent.
2. Carotenoids, like vitamin A, are known to moderately enhance the immune response and, depending on the carotenoid, this can emphasize a stimulatory effect on either the Th1 or Th2 systems.
3. The carotenoids are relatively potent antioxidants and may well have a major role to play in specific free radical quenching in tissues where they are present in high concentration, e.g. the eye (lutein and zeaxanthin), the adrenal gland (b-carotene and lycopene), the prostate and testes (lycopene and b-carotene)
Carotenoids and Cancer
In virtually every epidemiological analysis, increased consumption of fruit and vegetables significantly correlates with lowered risk of developing cancer. While the reasons for this are almost certainly multi-factorial, much interest has focused on the carotenoids as being an important reason for this effect.
Thus while epidemiological evidence is certainly present which correlates dietary intake of b-carotene with lowered risk of developing lung cancer (Canfield et al., 1993), when this has been subjected to intervention trials using b-carotene supplements, the effect has not been reproduced. Indeed in two studies, there was an increased risk associated with b-carotene supplementation (Heinonen et al., 1994: Omenn et al, 1996)
Hence there are opposing sets of data but these may be reconciled in the following way. The plasma contains 30 or so carotenoids. The major ones, which constitute 70% of the total, are shown below:
b-carotene
Lutein & Zeaxanthin Lycopene B-Carotene A-Carotene B-Cryptoxanthin
In the normal diet containing high quantities of fruit and vegetables, all of these carotenes are absorbed. Thus the epidemiological effects of carotenoids come from the presentation of a complex mixture rather than the application of a single species. It is for this reason that Pharmax Carotenoid Complex contains all six of the major carotenoids.
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