There is increasing evidence in the nutritional literature that intakes of fruits and vegetables are beneficial to the health. Part of the reason for these health effects is thought to derive from the presence of a range of phytochemical nutrients that are present in the tissues of edible plants. In many cases these phytochemicals are bioavailable, and can accumulate in the tissues of animals and humans. Once such group of phytochemicals are the carotenoids, a group of lipid soluble photosynthetic accessory compounds in plants that can give fruits and vegetables their red, orange and yellow colours. Tomatoes, peppers and carrots are commonly eaten foods with high concentrations of carotenoids. Carotenoids., being fat soluble, can accumulate in the fat tissues of animals following consumption, and it is thought that they may have specific antioxidant effects that protect cells from free radical damage. In particular, carotenoids inhibit the production of the superoxide radical, and this may explain their anti-cancer effects.
However, many carotenoids act as precursors to vitamin A, and this may also explain some of the anti-cancer effects of carotenoids. Vitamin A is involved in cell regulation including mechanisms involving cellular differentiation and immune-enhancement and may therefore limit tumorigenesis and malignant transformations. A number of large scale studies have investigated the association between carotenoid intake and cancer rates in Western populations. For example, in one such study1, researchers measured the carotenoid plasma levels of over 30,000 women, and then used medical records to assess the subsequent diagnosis of breast cancer over a 20 year period. The results of the study showed that higher levels of α-carotene, β-carotene, lycopene, and total carotenoids in the plasma of the women were associated with an 18–28 % lower risk of breast cancer. Carotenoid plasma levels were also associated with a reduction in cancer recurrence and with cancer mortality in the women.
Studies suggest that α-Carotene, β-carotene, β-cryptoxanthin, lutein, zeaxanthin, and lycopene are the most common dietary carotenoids in the Western diet, and these may comprise up to 90 % of the total plasma carotenoids. However, there are a large number of additional carotenoids that make up the remaining 10 % and the effects of these individual carotenoids, or their combinations are not fully understood. As uncertainty exists about the wisdom of supplementing with single isolated carotenoids, it is recommended that a range of carotenoids are consumed from fruits and vegetables, by eating a variety of differently coloured plant material. Further although there exists an association between carotenoids and cancer the cause and effect of the relationship is not understood. It may be the case that carotenoids may simply be a marker for fruit and vegetable intake, and that other phytochemicals within fruits and vegetables are the cause of this associations, suggesting that varied plant food diets may be the best strategy.
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