High plasma carotenoid concentrations are associated with reductions in the risk of developing certain cancers, and high concentrations of particular carotenoids in the retina of the eye can be protective of damaging radiation. However, many clinical studies looking at the effects of carotenoid supplements administer synthetic forms of a single carotenoid (usually synthetic β-carotene). Evidence suggests that high intakes of single antioxidants in isolation, particularly carotenoids and vitamin E, may have damaging pro-oxidant effects. This has been demonstrated in studies investigating supplementation of synthetic β-carotene in smokers where increases in lung cancer were reported following supplementation. In nature, although certain carotenoids are more common that other, generally carotenoids are found in plants as mixtures that provide a spectrum of compounds, alongside other antioxidants. Fruits and vegetables contain many carotenoids and research shows that eating a varied diet increases plasma levels of a number of carotenoids.
For example, the effects of fruits and vegetables with high carotenoid concentrations on the plasma levels of carotenoids in 36 healthy men has been investigated by researchers1. Subjects consumed a high carotenoid diet for two periods of 15 days that was estimated to provide a total carotenoid intake of 16mg/d of mixed carotenoids. The diet contained foods that were considered commonly available to a typical American, and fat intake was controlled to ensure carotenoid absorption. At baseline, there was a wide variation in plasma carotenoid concentrations suggesting biochemical individuality in absorption and differing carotenoid intakes. Following consumption of the high carotenoid diet, plasma levels of lutein, cryptoxanthin, α-carotene, 13-cis-β-carotene, cis-lycopene and trans-lycopene were all significantly increased from days 6 to 16. Addition of broccoli to the diet caused a significant further increase in the plasma concentrations of lutein.
These results suggest that carotenoids in plasma can be increased easily with addition of fruit and vegetables to the diet, and that supplementation is not necessary to attain adequate carotenoid status. The benefit of increasing fruit and vegetable intake is that it provides a wide variety of carotenoids which may be more beneficial than high intakes of a single nutrient. For example, the hydrocarbon carotenoids, which include β-carotene and α-carotene found in yellow and orange vegetables, are protective of cardiovascular disease and so may be protective of peroxidation of low density lipoprotein. In contrast, the oxygenated carotenoids from spinach, kale and other green leafy vegetables, which includes lutein and zeathanthin, accumulate in the retina where they protect the eye. High intakes of the acyclic carotenoid lycopene from tomatoes, which is generally the most abundant in plasma, reduces risk of cervical and prostate cancer.
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