Lycopene is one of the most common carotenoids in the human diet. In one US study, intake of lycopene was reported to be about 3.7 mg/day, accounting for almost 30% of total carotenoid intake. Unlike [Beta]-carotene, lycopene cannot be converted into vitamin A in the human body; nevertheless, it may be a biologically important substance.
The principal sources of lycopene in most people's diets are tomatoes and tomato products. Because of losses during processing, the lycopene content of concentrated tomato products such as tomato paste or ketchup is generally lower than would be expected on the basis of their tomato content. However, lycopene from some processed sources appears to be more bioavailable than lycopene from unprocessed tomatoes or tomato juice. Other food sources of lycopene include rose hips, watermelon, pink guava, and pink grapefruit.
Lycopene has antioxidant activity. It quenches singlet oxygen and scavenges free radicals. It also has effects on cell-to-cell communication and can suppress cell proliferation.
Lycopene accumulates in human tissues. High levels are found in the liver, adrenals, and testes, and lower levels are found in other tissues such as the kidney and lung. Excess amounts of lycopene can accumulate in the adipose tissue under the skin, producing lycopenemia--a variant of carotenemia.
A large epidemiologic study in the US recently associated high intakes of lycopene with a reduced risk of prostate cancer. Other studies have associated high intakes of lycopene (or tomatoes) with reduced risks of cancers of the bladder, pancreas, and digestive tract. It is unclear, however, whether these reductions in risk represent true effects of lycopene or whether high lycopene intake is merely a marker for a healthful diet rich in vegetables and fruits. In some cultures, lycopene intake may also be a marker for Mediterranean-style eating habits, since tomatoes are an important component of the Mediterranean diet. Aspects of the Mediterranean diet other than tomato intake, however, may be responsible for the reduced risks of disease associated with this eating pattern.
In summary, presently available data--including both biochemical and epidemiological findings--point to a possible role of lycopene in human health. More research is needed to establish its role firmly and to identify the underlying biochemical mechanisms.
Wilhelm Stahl and Helmut Sies, Lycopene: A Biologically Important Carotenoid for Humans? Archives of Biochemistry & Biophysics 336(1):1-9 (1 Dec 1996) [Correspondence: Professor Helmut Sies, Institut fur Physiologische Chemie I, Heinrich-Heine-Universitat Dusseldorf, Postfach 101007, D-40001 Dusseldorf, Germany. Fax +49 211 811 3029; E-mail:helmut.sies@ uni-duesseldorf.de]
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