Other common name(s): rhodopurpurin
Scientific/medical name(s): non-provitamin A carotenoid
Lycopene is an antioxidant compound that gives tomatoes and certain other fruits and vegetables their color. It is one of the major carotenoids in the diet of North Americans and Europeans. Carotenoids are pigments that give yellow, red, and orange vegetables and fruits their colors. The body uses some types of carotenoids (but not lycopene) to make vitamin A.
People who have diets rich in tomatoes, which contain lycopene, appear in some studies to have a lower risk of certain types of cancer, especially cancers of the prostate, lung, and stomach. However, not all of the studies have reached the same conclusion. Studies that tested lycopene on men who already had prostate cancer have been mixed, but in general found little effect. Further research is needed to find out what role, if any, lycopene has in the prevention or treatment of cancer. It is likely that the preventive effect of diets high in fruits and vegetables cannot be explained by just one single part of the diet.
How is it promoted for use?
Proponents claim that lycopene may lower the risk of heart disease; macular degenerative disease, an age-related illness that can lead to blindness; and lipid oxidation, the damage to normal fat molecules that can cause inflammation and disease. It is also said to lower LDL ("bad" cholesterol), enhance the body's defenses, and protect enzymes, DNA, and cellular fats.
A major claim for lycopene's benefits is in the prevention and treatment of cancers of the lung, prostate, stomach, bladder, cervix, skin, and, especially, prostate. In support of these claims regarding cancer, proponents note that lycopene is a powerful antioxidant, a compound that blocks the action of free radicals, activated oxygen molecules that can damage cells, and that several scientific studies have found lower risk of cancer among people who eat lycopene-rich foods.
What does it involve?
Tomatoes are the most concentrated food source of lycopene, although apricots, guava, watermelon, papaya, and pink grapefruit are also significant sources. Studies that looked at lycopene levels in the blood found that levels were higher after people ate cooked tomatoes than after they ate raw tomatoes or drank tomato juice. This suggests that lycopene in cooked tomato products such as tomato sauce or paste may be more readily absorbed by the body than lycopene in raw tomatoes. Eating lycopene-rich vegetables and fruits together with a small amount of oil or fat (for example, salad oil or cheese on pizza) increases the amount of lycopene absorbed by the intestines. Lycopene is also available in soft-gel capsule and liquid supplements. Dosages vary according to manufacturer.
What is the history behind it?
In recent years, the role of the diet in preventing cancer has been a popular and important area of research. The examination of the role of carotenoids, specifically beta carotene, in preventing cancer began in the 1920s. However, interest in lycopene did not really begin until the late 1980s when it was found that the antioxidant activity of lycopene was twice that of beta carotene.
What is the evidence?
Studies that look at large groups of people (observational studies) in many countries have shown that the risk for some types of cancer is lower in people who have higher levels of lycopene in their blood. Studies suggest that diets rich in tomatoes may account for this reduction in risk. Evidence is strongest for lycopene's protective effect against cancer of the lung, stomach, and prostate. It may also help to protect against cancer of the cervix, breast, mouth, pancreas, esophagus, and colon and rectum.
Some population studies have found that a diet high in lycopene from tomato-based foods was linked with a lower risk of prostate cancer. Other studies, however, found no link between tomato products or other lycopene-rich foods and prostate cancer. A recent study suggested that variation in a particular gene (known as XRCC1) that helps repair damaged DNA influences whether lycopene intake will affect a man's prostate cancer risk.
A 2004 review that analyzed 21 observational studies (that is, not clinical trials) concluded that tomato products appear to have a weak protective effect against prostate cancer. This review did not include lycopene supplements, only tomato and tomato-based foods. Some of the individual studies, however, did consider lycopene levels in the blood. The analysis noted that the protective effect was slightly stronger for cooked tomato products and that small amounts of added fat improved lycopene absorption. On the other hand, 2 studies from 2007, one of about 1,500 men and the second of more than 28,000 men, found no difference in blood lycopene levels between those in whom prostate cancer later developed and those in whom it did not. Such mixed results sometimes happen when there is no effect or only a small effect from the substance being looked at.
There have been several experimental studies on the role of lycopene in preventing or treating cancer. One animal study found that lycopene treatment reduced the growth of brain tumors. Another animal study showed that frequent intake of lycopene over a long period of time considerably suppressed breast tumor growth in mice. But breast cancer in humans is very different from breast cancer in mice, and those results may not apply to the disease in humans. There has been a human study that assigned men at high risk for prostate cancer to take an ordinary multivitamin either with or without a lycopene supplement. This study found no difference in prostate-specific antigen (PSA, a marker of prostate cancer) levels between the 2 groups. Further studies are needed to find out if any possible anti-cancer properties could benefit humans.
Since tomatoes also contain vitamins, potassium, and other carotenoids and antioxidants, it may be that other compounds in tomatoes may account for some of the protective effects first thought to be due to lycopene. These compounds may act alone or along with lycopene. When researchers look at large population groups with different lifestyles and habits, it is also possible that their findings can be explained by other factors that were not examined.
To test whether lycopene is the main cancer-fighting substance in tomatoes, one animal study compared lycopene supplements to powdered tomatoes. Groups of rats who were fed tomato powder were compared to rats given lycopene. The rats that received tomato powder had much lower cancer risk, whereas the rats receiving lycopene supplements did not differ significantly from the group that received no special supplements.
A controlled study in a small group of men with prostate cancer found that lycopene supplements appeared to reduce the rapid growth of prostate cancer cells. However, a more recent study with men whose prostate cancer had stopped responding to hormone therapy found that lycopene did not have a significant effect. One short-term study from 2006 reported that lycopene supplements were safe, but that they did not lower the levels of prostate-specific antigen (a marker of prostate cancer) in men with prostate cancer that had come back. Another reported that the combination of lycopene and soy supplements prevented PSA levels from increasing in some men with prostate cancer.
The few clinical trials that have been completed have reported mainly the short-term effects on the level of PSA in the blood, which is generally considered a good indicator of prostate cancer growth. Although these studies are an important step, they are not as valuable as long-term studies that look at whether a treatment actually helps patients live longer or relieves their symptoms.
Most of the human studies that have been published so far were case control studies or other observational studies, which are more prone to error than clinical trials are. More information from clinical trials (including results of several studies already under way) will be needed to be sure whether lycopene-rich foods can help prevent or treat cancer. There are also studies to find out if there are other benefits from lycopene.
Choosing foods from a variety of fruits, vegetables, and other plant sources such as nuts, seeds, whole grains, and beans is likely to be healthier than eating large amounts of one type of food. The American Cancer Society's most recent nutrition guidelines recommend eating a balanced diet with an emphasis on plant sources, which includes:
- 5 or more servings of vegetables and fruit each day
- choosing whole grains over processed and refined grains
- limiting processed meats and red meats
- balancing calorie intake with physical activity to get to or stay at a healthy weight
- limiting alcohol intake
Based on today's evidence, the foods you eat are likely to play a greater role in preventing cancer than in treating it.
Are there any possible problems or complications?
This product is sold as a dietary supplement in the United States. Unlike drugs (which must be tested before being allowed to be sold), the companies that make supplements are not required to prove to the Food and Drug Administration that their supplements are safe or effective, as long as they don't claim the supplements can prevent, treat, or cure any specific disease.
Some such products may not contain the amount of the herb or substance that is written on the label, and some may include other substances (contaminants). Actual amounts per dose may vary between brands or even between different batches of the same brand. The FDA has written new rules to improve the quality of manufacturing processes for dietary supplements and the accurate listing of supplement ingredients. But, the new rules do not address the safety of supplement ingredients or their effects on health when proper manufacturing techniques are used.
Most such supplements have not been tested to find out if they interact with medicines, foods, or other herbs and supplements. Even though some reports of interactions and harmful effects may be published, full studies of interactions and effects are not often available. Because of these limitations, any information on ill effects and interactions below should be considered incomplete.
Lycopene obtained from eating fruits and vegetables has no known side effects and is thought to be safe for humans. The potential side effects of lycopene supplements are not fully known. Patients in one study who took a lycopene-rich tomato supplement of 15 milligrams twice a day had some intestinal side effects such as nausea, vomiting, diarrhea, indigestion, gas, and bloating. When consumed over a long period of time, very large amounts of tomato products can give the skin an orange color.
Supplements containing antioxidants such as lycopene may interfere with radiation therapy and chemotherapy if taken during cancer treatment. Even though studies have not been done in humans, antioxidants are known to clean up free radicals, which could interfere with one of the methods by which chemotherapy and radiation destroy cancer cells. Eating fruits and vegetables high in antioxidants is still considered safe during cancer treatment.
Relying on this type of treatment alone and avoiding or delaying conventional medical care for cancer may have serious health consequences.
More information from your American Cancer Society
The following information on complementary and alternative therapies may also be helpful to you. These materials may be found on our Web site (www.cancer.org) or ordered from our toll-free number (1-800-ACS-2345).
The ACS Operational Statement on Complementary and Alternative Methods of Cancer Management
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Note: This information may not cover all possible claims, uses, actions, precautions, side effects or interactions. It is not intended as medical advice, and should not be relied upon as a substitute for consultation with your doctor, who is familiar with your medical situation.
Last Revised: 05/13/2010