Lycopene is the carotenoid that is responsible for giving tomatoes their red color. Although there are about 600 known carotenoids, lycopene is the most abundant form found in the U.S. diet (beta-carotene is #2). More than 80% of the lycopene consumed in the U.S. comes from tomato sauce, pizza and ketchup. The lycopene content of tomatoes can be influenced dramatically during the ripening process and large differences are noted between various types of tomatoes (e.g. red have more lycopene than yellow varieties). The bioavailability of lycopene is increased following cooking – so processed tomato products such as ketchup, tomato juice and pizza sauce have more bioavailable lycopene than do fresh tomatoes. Because of the epidemiological evidence that diets high in lycopene-rich foods are associated with a reduced risk of many cancers, lycopene supplements are often promoted for cancer protection, heart health, and as a general antioxidant.
Until recently, virtually all lycopene supplements were extremely expensive – and many still are. Recently, however, supplement manufacturers have introduced a synthetic lycopene that should cut the cost of lycopene-containing supplements about 5 times and still deliver the same effectiveness. As an antioxidant, lycopene is twice as potent as to beta-carotene in protecting white blood cells from membrane damage due to free radicals. For those individuals undergoing pharmaceutical treatment of high cholesterol or triglycerides, it is important to be aware that common treatments such as cholestyramine and Probucol have been shown to reduce plasma lycopene levels by 30-40%. That said, the most cost-effective method for obtaining your daily lycopene is unquestionably a diet high in tomato-based foods.
You may have seen some bottles of ketchup labeled with claims that “Lycopene may help reduce the risk of prostate and cervical cancer” – not bad for a bottle of ketchup. Because lycopene is a potent antioxidant and seems to inhibit growth of cancer cells, it is logical that a higher intake of this carotenoid may indeed be associated with reduced incidence of cancer (Norrish et al. 2000). In addition, lycopene may also help prevent heart disease through this same antioxidant mechanism via an inhibition of LDL cholesterol oxidation (Arab and Steck 2000). Finally, lycopene is known to play a role, along with beta-carotene, in protecting the skin from the damaging effects of ultra-violet light radiation (Dorgan et al. 2004).
The theory behind lycopene’s cancer preventive benefits is logical. Indeed, plasma lycopene levels are clearly reduced, by about 40-50%, in smokers whose lungs are exposed to a high degree of oxidative damage (Dietrich et al. 2004) and several epidemiologic studies have shown that consumption of foods high in lycopene (tomatoes, pizza sauce and tomato juice) is associated with lower rates of prostate cancer (Gann et al. 1999). Dietary supplements containing 10 – 40mg of lycopene have been shown to reduce DNA damage in white blood cells (Porrini et al. 2000) – probably due to the reduction in oxidative damage to DNA and lipoproteins. However, it is important to remember the recent history concerning lycopene’s carotenoid cousin, beta-carotene, which was associated with reduced disease incidence when consumed in foods, but appeared less effective, and in some cases, detrimental, when consumed as isolated high dose dietary supplements.
In a study of patients suffering from prostate cancer, lycopene supplements have been shown to slow tumor growth (Kucuk et al. 2002). In subjects consuming the lycopene supplement, prostate tumors shrunk and produced lower levels of prostate specific antigen (PSA), a marker compound produced by active prostate cancer cells (Kelloff et al. 1999). An interesting note with this study was that the supplement used was not a purified lycopene supplement, but a high-lycopene tomato concentrate - suggesting that other tomato compounds in addition to lycopene may contribute to the protective effect. Another study concluded that regular consumption of a variety of processed tomato products -- like ketchup, tomato juice and tomato sauce -- significantly raises blood levels of lycopene (Paetau et al. 1999).
No significant adverse side effects are associated with regular consumption of supplemental levels of lycopene – but owing to the controversy surrounding high-doses of supplemental beta-carotene (which appears to increase lung cancer risk when supplemented at high and unbalanced doses in lifelong heavy smokers), doses of lycopene should remain in the range of levels attainable from a diet high in tomato-based products (10-40mg/day). The most compelling cancer prevention data suggests that 10 servings of tomato products per week (approximately 20-100mg of lycopene, depending on food choices and preparation methods) can reduce the risk of prostate cancer by approximately 35% (Giovannucci et al. 1999).
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EDITOR'S NOTE: This monograph can be found in The Health Professional's Guide to Dietary Supplements (Lippincott, Williams & Wilkins) by Shawn M. Talbott, PhD and Kerry Hughes, MS.