Hydrocarbon Carotenoid Lycopene

Lycopene, while having no provitamin A activity, is a potent antioxidant with twice the activity of ^-carotene for quenching singlet oxygen and 10 times the antioxidant activity of a-tocopherol in some model systems. The antioxidant potential of food chemicals varies widely according to location in the body and the presence of other body chemicals. The primary sources of dietary lycopene are tomatoes and tomato products. Epidemiological evidence shows an inverse association between lycopene consumption and the incidence and development of certain cancers. This association is especially strong for prostate cancer, which is the most common cancer among men in Western countries and the second leading cause of cancer death in American men. Prostate cancer rates in Asian countries are much lower, but appear to be increasing rapidly. Lycopene is localized in prostate tissue. The current consensus is that a high consumption of tomatoes or high circulating concentrations of lycopene are associated with a 30-40% risk reduction for prostate cancer, especially the most aggressive forms. Recent studies in rats show that tomato products are more protective against prostate cancer than isolated lycopene.

Epidemiologic studies have also observed lower rates of bladder, cervical, and breast cancers as well as cancers of the gastrointestinal tract among people with high intake of lycopene. The discovery of significant concentrations of lycopene in specific tissues in the body, i.e., plasma, testes, adrenal glands, liver and kidney, suggests that lycopene may play a role in these tissues.

While the body of evidence seems strong, several studies have found either no or weak associations between lycopene consumption and disease. Some of this may be explained by the fact that blood lycopene concentrations were much lower in these studies than in those that showed a beneficial effect. Thus, future dietary based studies need to include blood sampling to further define the range of blood concentrations of lycopene in the population, ideally with method standardization so that studies can be directly compared. The prostate cancer association is usually stronger for cooked tomato products rather than raw tomatoes or total lycopene intake. This too supports the idea that it is the whole food, with a broad array of nutrients and nonnutritive bioactive components, that is important for overall health rather than isolated compounds. It is possible that the beneficial effects of tomatoes are increased by preparing a concentrated product that enhances the nutrient bioavailability, as processed and cooked tomatoes are more closely associated to decreased risk of disease than either raw tomatoes or tomato juice.

Because lycopene is a potent antioxidant, it may be protective against heart disease by slowing down the oxidation of polyunsaturated fats in the low-density lipoprotein particles in the blood. Epidemiological and clinical studies show that higher blood lycopene concentrations are associated with lower risk and incidence of cardiovascular disease. Higher fat stores of lycopene have also been associated with lower risk of myocardial infarction. The most profound protective effect is in nonsmokers. The evidence for protective cardiovascular effects is compelling, as studies have shown a 20-60% improvement in cardiovascular parameters with higher blood concentrations of lycopene. Furthermore, higher intake of fruits and vegetables is associated with better lung function. In particular, high tomato intake is associated with higher timed expiratory volume.

The major food source of lycopene globally is tomatoes and tomato products. In the US, more than 80% of dietary lycopene comes from tomatoes.

Other sources include watermelon, pink grapefruit, and red carrots.

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