All about Lycopene

Lycopene is a carotenoid, a natural color pigment that contributes to the deep red color of tomatoes and various other fruits and vegetables. It is only in the last decade that lycopene has become widely recognized as a potential protector against the risk of certain types of cancer and cardiovascular diseases. Lycopene is one of 600 known carotenoids found in plants, deposited as elongated, needle-like crystals in mature fruit. Lycopene gets its color and antioxidant properties from its chemical structure, which consists of a long chain of eleven conjugated double bonds.

Lycopene is found in a multitude of fruits, including watermelon, guava, papaya, apricots, pink grapefruits and red oranges. However, 85 percent of most people's dietary intake of lycopene comes from tomatoes and tomato products. According to studies conducted in the mid-1990s, lycopene intake in America averaged 3.1 to 3.7 mg per day for women and 5.2 mg per day for men. Intake was not only higher in men, but it was actually highest in people 12 to 19 years old.

Few mammals besides humans can absorb carotenoids. Rats and ferrets are used for studies, but they absorb carotenoids much less efficiently than humans. Even in humans, absorption is 10 to 30 percent of consumption, with the rest being excreted. This low absorption occurs because carotenoids are bound to other molecules, such as plant proteins, that limit their absorbency.

Carotenoids are absorbed by the body like fats, passively diffusing through the intestinal cell membrane into mucosal cells, where they are then taken up by chylomicrons and transported by the lymphatic system into the liver. Once lycopene is absorbed and carried to the liver, it can reenter the circulation packaged in low density lipoproteins (LDL), the same blood plasma carrier as "bad" cholesterol and alpha tocopherol. Whether LDL is protected by lycopene from oxidation caused by free radicals has not been conclusively proven.

As an antioxidant, lycopene has been proven the most potent of all the carotenoids in quenching singlet oxygen, a highly reactive and short-lived molecule capable of causing extensive cell damage.

Most studies have shown that plasma and tissue levels of lycopene directly reflect dietary intake, but continuous intakes of the antioxidant have little effect on plasma levels. In one study, the plasma depletion half-life of lycopene ranged from 12 to 33 days, suggesting slow plasma lycopene turnover. Levels are also influenced by factors such as age, gender, hormones, body mass, blood lipid levels, smoking, alcohol and the presence of other carotenoids in food.

The absorption of lycopene from cooked tomato paste was shown to be 3.8 times that from fresh tomato. The higher bioavailability of heated tomato products causes a higher concentration of lycopene in the plasma than from fresh tomatoes.

It has been found that lycopene constitutes up to 80 percent of the total carotenoids found in the adrenal glands and testes. This concentration is thought to be due in part to the higher number of LDL receptors existing in these places, creating a higher uptake of lipoproteins in these than in other organs.

In the laboratory, lycopene has been found to suppress growth of human cancer cells, such as protecting from bacterial infections, inhibiting growth of brain tumors and reducing the size and quantity of carcinogen-induced tumors.

More than 72 epidemiological studies have been conducted on lycopene, with 57 of these studies showing inverse associations. The strongest connections were found between lycopene and prostate, lung and stomach cancers. Weaker associations were found for colon, oral, pancreatic, esophageal and cervical cancers, with no associations found for bladder, breast and ovarian cancers. No cancer risk was found with high consuptions of serum lycopene.

Of course, the inverse association of lycopene with prostate cancer has received the most media attention. This is due in part to two large population studies (62,000 men in all). In one of the studies, conducted by Dr. Edward Giovannucci at Harvard Medical School, consuming tomatoes, tomato sauce or pizza more than twice a week was found to lower the risk of prostate cancer by 21 to 34 percent.

To date, only one intervention study with lycopene has been completed. In 1999, 33 prostate cancer patients at the Karmanos Cancer Institute in Detroit were assigned either 30 mg of lycopene or a placebo for 30 days before an operation. The cancer stopped spreading in 67 percent of the supplemented patients vs. 44 percent of the controls.

Thus far, studies of lycopene and cardiovascular disease have been limited. In the EURAMIC study, a multi-center European trial, the risk for acute heart attack at the highest level of lycopene in adipose tissue was reduced by 65 percent, compared to adipose lycopene at the lowest level. Two other studies found an inverse relationship between lycopene in the serum and the risk of cardiovascular mortality or the risk for stroke.

In terms of cholesterol levels, a small clinical trial using 200 healthy patients, found that lycopene from tomato products (one to two servings per week) reduced in vitro oxidative damage to lipids, lipoproteins and DNA.

Although lycopene was first isolated in 1873, it is only in the last decade that it has become widely recognized as a potentiaT protector against the risk of certain types of cancer and cardiovascular diseases. Even though the science is still emerging and little intervention data is available, consumer interest in lycopene has been growing.