Lycopene, found primarily in tomatoes, is a member of the carotenoid family, which includes beta-carotene and similar compounds found naturally in food, and has potent antioxidant capabilities. It is an antioxidant and anti-tumor agent.
Lycopene is one of the 600 plus carotenoids known to man. Unlike most of the others, carotenoids, man does not metabolize it to vitamin A. Lycopene provides stronger antioxidant protection against certain types of free radicals, and may protect against particular cancers better than any nutrient presently known. Lycopene makes up about half the carotenes in human blood.
Tomatoes and tomato-containing foods are high in lycopene. In the Harvard study, the only tomato-based food that did not correlate with protection was tomato juice. In an unblinded, controlled trial, lycopene supplementation, but not tomato juice, effectively increased the body's lycopene stores. [Am J Clin Nutr 1999;70: pp.490-4] These studies suggest that the lycopene present in tomato juice is poorly absorbed. However, other research indicates that significant amounts of lycopene from tomato juice can, in fact, be absorbed. [Am J Clin Nutr 1998;68: pp.1187-95]
Although humans get most of their lycopene from tomatoes – by far the richest source – tomato products offer a more concentrated source of lycopene than the fresh fruit itself. For example, tomato powder contains approximately 120mg per 100 grams of fruit whereas fresh tomatoes have only 2mg per 100 grams.
Since lycopene is a nutrient that can stand the heat, cooked tomato products, such as tomato paste, provide more of it than do fresh tomatoes. Spaghetti sauce is an adequate source of lycopene because it contains fat, which is necessary for absorption. It has been theorized that heating tomatoes makes their lycopene more absorbable.
Other foods that contain lycopene include watermelon, pink grapefruit, and guava.
Lycopene is what gives tomatoes, watermelons, grapefruits and papaya their red color. A pigment synthesized by some plants and animals to protect them from the sun, lycopene evolved as a weapon against certain types of free radicals. Lycopene is more effective at quenching free radicals, than vitamin E in one study on oxidized fat.
As reported in the journal Lipids, a group from Canada demonstrated that lycopene significantly lowers LDL oxidation in human blood. People with high cholesterol have been found to have high levels of free radicals and low levels of lycopene and beta carotene.
Several studies show a connection between lycopene and cancer prevention. Lycopene appears to be protective against cancer of the digestive tract. Several studies have found a lower risk for colorectal cancer in people who eat a lot of tomato products and/or have higher levels of lycopene in their blood. More direct evidence has been provided by researchers in Japan who did a study on colon cancer in rats. They found that tomato juice provided significant protection against a chemical carcinogen (N-methylnitrosourea).
Lycopene decreases the incidence of lung and stomach cancer according to one Harvard research study.
Just as lutein is concentrated in the macula, lycopene is concentrated in the prostate gland. Several studies have however linked lycopene with a lower risk of prostate cancer. One of these studies, the Washington County study, found that men with the most lycopene in their blood halved their risk of prostate cancer compared to those with the least.
It's important to note that, in studies performed in Japan and the University of Bern in Switzerland, pure lycopene was not found to be effective by itself. The authors of one study speculate that lycopene's action depends on other factors present in the juice that is missing in pure lycopene. Recent thinking in carotene research is that the carotenes are both interdependent and dependent on other vitamins and minerals, and this must be taken into account when studying them.
Lycopene may also be protective against pancreatic cancer. Researchers at Johns Hopkins tested the stored blood (drawn before treatment) of 22 people with pancreatic cancer for levels of certain vitamins and selenium. Lycopene and selenium levels were lower in the cancer patients than in controls.
The ideal intake of lycopene is currently unknown; however, the men in the Harvard study with the greatest protection against cancer consumed at least 6.5mg per day.
Another source recommends a dose of 10mg or 15mg capsules, twice a day.
Lycopene works better in combination with lutein, another carotenoid which is found mostly in spinach and corn. (Lutein is associated with maintenance of the macula.)
There appear to be no side-effects reported with the use of lycopene.
Lycopene supplementation has been found to boost immune function in the elderly. In one trial, 15mg of lycopene per day increased natural killer cell activity by 28% in 12 weeks. [Proc Nutr Soc 1998;57:3A (abstr)]
A study performed in India showed that lycopene supplementation proved to be beneficial to couples who try for the first time to conceive but are not successful due to unspecified male infertility problems. In this study, 50 men with low sperm counts were selected to receive lycopene supplements twice per day for three months. Within nine months after starting the lycopene supplements, 36% of the couples were successful. Amongst the 50 men, 70% had an increase in sperm concentration and 58% had an increase in sperm motility.
Lycopene helps reduce the symptoms of asthma caused by exercising. In one double-blind trial [Allergy 2000;55: pp.1184-9], over half of people with exercise-induced asthma had significantly fewer asthma symptoms after taking capsules containing 30mg of lycopene per day for one week compared to when they took a placebo.
In Europe, researchers have found a statistically significant association between high dietary lycopene and a 48% lower risk of heart disease. [Am J Epidemiol 1997;146: pp.618-26]
A review of 72 studies reported 57 associations between tomato intake or blood lycopene levels and decreased risk of cancer. [J Natl Cancer Inst 1999;91: pp.317-31] Of these associations, 35 were statistically significant. The benefit was strongest for prostate, lung, and stomach cancers, although protective associations were also found for cancers of the pancreas, colon, rectum, esophagus, oral cavity, breast, and cervix.
Because the data were from observational studies, a cause-and-effect relationship cannot be firmly established. However, the consistently lower risk of cancer associated with higher consumption of lycopene-containing tomatoes, provides a strong foundation for further research on lycopene.
One study found that for the 25% of people with the greatest tomato intake, the risk for cancers of the gastrointestinal tract was 30-60% lower, compared with those who ate fewer tomatoes. These reduced risks were statistically significant. [Int J Cancer 1994;59: pp.181-4]
A study of women found that the 75% who ate the least amount of tomatoes had between 3.5 and 4.7 times the risk for cervical intraepithelial neoplasia – pre-cancerous changes of the cervix. [Int J Cancer 1991;48: pp.34-8] Other researchers have also reported evidence suggesting that high dietary lycopene may be linked to protection from cervical dysplasia. [Nutr Cancer 1998;31: pp.31-40]
A study conducted by Harvard researchers examined the relationship between carotenoids and the risk of prostate cancer. Of the carotenoids studied, only lycopene was clearly linked to protection. The men who had the greatest amounts of lycopene in their diet (6.5mg per day or more) showed a 21% decreased risk of prostate cancer compared with those eating the least. [J Natl Cancer Inst 1995;87: pp.1767-76]
This suggests that lycopene may be an important tool in the prevention of prostate cancer. The study also reported that those who ate more than ten servings per week of tomato-based foods had a 35% decreased risk of prostate cancer compared with those eating less than 1.5 weekly servings. When the researchers looked at only advanced prostate cancer, the high lycopene eaters had an 86% decreased risk (although this did not reach statistical significance due to the small number of cases).
Contrary to popular opinion, research suggests that there is no preferential concentration of lycopene in prostate tissue [Am J Epidemiol 2000;151: pp.124-7 (review, discussion 128-30)]. Although prostate cancer patients have been reported to have low levels of lycopene in the blood [Nutr Cancer 1999;33: pp.159-64], and lycopene appears to be a potent inhibitor of human cancer cells in test-tubes [Nutr Cancer 1995;24: pp.257-66], evidence is conflicting concerning whether an increased intake of tomato products is protective against prostate cancer. Some studies, like the one discussed above, have reported that high consumption of tomatoes and tomato products reduces risk of prostate cancer. Other studies, however, are inconclusive [Am J Epidemiol 2000;151: pp.119-23], and some have found no protective association.
While preliminary evidence links dietary lycopene with protection from breast cancer [Cancer Causes Control 1998;9: pp.89-97], another study did not find this link. [Cancer Lett 1997;114: pp.251-3]
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