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Lycopene: Benefits, Side Effects, Sources
Lycopene, a carotenoid without provitamin-A activity, is present in many fruits and vegetables. It is a red, fat-soluble pigment found in certain plants and microorganisms, where it serves as an accessory light-gathering pigment and protects these organisms against the toxic effects of oxygen and light.
Tomato products, including ketchup, tomato juice, and pizza sauce, are the richest sources of lycopene in the U.S. diet, accounting for greater than 80 percent of the total lycopene intake of Americans. Processed tomatoes (e.g. canned tomatoes, tomato sauce, ketchup) contain more lycopene than tomatoes because cooking breaks down cell walls, releasing and concentrating carotenoids.
As a powerful antioxidant, lycopene helps neutralize harmful free radicals, which are implicated in cancer, heart disease, macular degeneration and other age-related illnesses. The evidence for a benefit was strongest for cancers of the prostate, lung, and stomach. Data were also suggestive of a benefit for cancers of the pancreas, colon and rectum, esophagus, oral cavity, breast, and cervix.
A review of 72 different studies showed consistently that the more tomatoes and tomato products people eat, the lower their risks of many different kinds of cancer. In a notable Harvard study of nearly 48,000 men, for example, those who ate more than two servings of tomato sauce a week were up to 36% less likely to develop prostate cancer over a 12-year period than men who ate less than one serving a month.
As stated, diets rich in lycopene may also be heart-protective. In the latest Harvard study of more than 28,000 women, those with the highest blood lycopene levels were about half as likely to develop heart disease over five years as women with the lowest levels. Research also suggests that lycopene may aid blood pressure and bone health.
Lycopene is generally considered safe, non-toxic, and consumption is usually without side effects. Scientific evidence for lycopene use in pregnancy is not available; however, no adverse events have been reported in association with the consumption of lycopene-containing foods during pregnancy.
Whether lycopene supplements are as beneficial as whole-food sources is debatable. Despite the spotlight on lycopene, it may not be protective on its own. It may only be a marker for other active substances in tomatoes or it may work together with other phyto-nutrients to confer health benefits. If so, then the race to supplement with lycopene pills may be misguided, as was recently suggested by Ohio State University researchers.
In their animal study, 194 rats were treated with drugs to induce prostate cancer and then fed whole tomato powder, pure lycopene or a placebo for 14 months. The animals fed tomato powder were 26% less likely to die than the placebo-controlled rats. But the lycopene-supplemented rats fared only slightly better than the controls.
“Research suggests that consuming tomato products rather than a supplement is the best way to achieve the proposed health benefits attributed to tomatoes,” says Steven K. Clinton, M.D., Ph.D., one of the study's authors.
Lycopene is also present in watermelon, papaya, pink grapefruit, and guava.
Comment from S. Zook, MS, PhD: As a nutrition research scientist I am always interested in good Internet resources to which I may direct students for further information. Your web page on lycopene is excellent, every word counts!
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