The carotenes are a highly colored (red to yellow) group of fat-soluble plant pigments. All organisms whether bacteria or plants, that rely on the sun for energy, contain carotene molecules. These compounds via their antioxidant effects play a crucial role in protecting the organism against damage during the process of photosynthesis – the process of converting the sunlight into chemical energy.

In humans, carotenes play two primary roles. Some are converted into vitamin A, and all exert antioxidant activity. Of the 600 carotenes that have been identified, about 30-50 are believed to have vitamin A activity. Carotenes that the body is able to convert to vitamin A are referred to as “provitamin A” carotenes. The most well known of this group are beta-carotene and alpha-carotene. Some of the better known carotenes without provitamin A activity, but with very high antioxidant activity, are lutein, lycopene, and zeaxanthin.

Historically, while beta-carotene has been termed the most active of the carotenes due to its higher provitamin A activity, recent research suggests that this function of carotenes has been overemphasized. Several carotenes, most notably lycopene and lutein, have been found to exhibit more important physiological activities than beta-carotene. While beta-carotene gets the most attention, it is important to point out that it comprises only 20–25% of the total serum carotene level.

So, what is the most predominant carotene in the blood? Surprising to many it is lycopene which accounts for more than 50% of the carotenes in human serum. Owing to its fat-loving nature, lycopene is found to concentrate in LDL and VLDL fractions and not in HDL fraction of the serum cholesterol. Studies have shown lycopene to exhibit the highest overall singlet oxygen quenching of the carotenes thus far studied. Its activity is roughly double that of beta-carotene. Furthermore, lycopene exert even more impressive anti-cancer effects.

Lycopene in the prevention and treatment of prostate cancer

In one of the more detailed studies of lycopene protection against cancer, Harvard researchers discovered that men who consumed the highest levels of lycopene (6.5 mg per day) in their diet showed a 21 percent decreased risk of prostate cancer compared with those eating the lowest levels. When the researchers looked at only advanced prostate cancer, the high lycopene eaters had an 86% decreased risk. Similar results were seen in lycopene protection against cancers of the gastrointestinal tract, cervical cancer, and breast cancer.

In addition to a protective effect, lycopene may exert a therapeutic effect as well. In a study of patients with existing prostate cancer, lycopene supplementation (15 mg per day) was shown to slow tumor growth, shrink the tumor, and lower the level of PSA (prostate specific antigen, a marker of cancer activity) by 18%.

In the most recent study, the efficacy of lycopene (4 mg daily) plus orchidectomy (surgical castration) was compared with orchidectomy alone in the management of advanced prostate cancer.72 Fifty-four patients with histologically confirmed metastatic prostatic cancer and a performance status of 0-2 (World Health Organization) were entered into the trial. At 6 months there was a significant reduction in PSA level in both treatments, but more marked in the lycopene group (9.1 vs 26.4 ng/mL). After 2 years these changes were more consistent in the lycopene group (3.01 vs 9.02 ng/mL). Eleven (40%) patients in the orchidectomy alone group and 21 (78%) in the lycopene group had a complete PSA response, with a partial response in nine (33%) and four (15%), and progression in seven (25%) and two (7%), respectively. Researchers concluded that adding lycopene to orchidectomy produced a more reliable and consistent decrease in serum PSA level; it not only shrinks the primary tumour but also diminishes the secondary tumours, providing better relief from bone pain and lower urinary tract symptoms, and improving survival compared with orchidectomy alone.

Lycopene in the prevention of cardiovascular disease

Just like the in cancer, a potential problem with much of the research on carotenes in cardiovascular disease protection has been the focus on beta-carotene. It may not be the most important marker of protection. In a very large clinical study evaluating the relationship between carotene status and heart attack found that lycopene, but not beta-carotene, was protective. Lycopene exerts greater antioxidant activity compared to beta-carotene in general, but specifically against LDL oxidation.

Beta-carotene is likely of less importance in the prevention of heart disease compared to many other carotenes, especially lycopene and lutein, because it does not get incorporated into LDL very effectively. In addition to its ability to protect against LDL damage, lycopene may also inhibit cholesterol synthesis and may enhance the breakdown of LDL in the liver.

How much lycopene is needed?

In population studies, the people showing protection from various cancers and heart disease were estimated to have eaten about 6 mg of lycopene per day from food. However, according to a detailed analysis of the levels of carotenes in 120 fruits and vegetables, lycopene is found in very few foods. Among the best sources is the tomato and tomato products. Cooked tomato products, tomato juice, and lycopene supplements provide the most bioavailable lycopene. In terms as lycopene supplementation, a good daily goal may be 6 mg per day. Higher dosages (e.g, 15-30 mg per day) have been recommended, but as shown in the latest study in the treatment of prostate cancer, a dosage as low as 4 mg daily can produce dramatic effects.

 

Table. Lycopene content of common foods
Food	Lycopene (mg/100 g)
Apricot, dried	0.8
Grapefruit (pink and raw)	3.4
Guava juice	3.3
Tomato, raw	3.1
Tomato juice, canned	8.6
Tomato paste, canned	6.5
Tomato sauce, canned	6.3
Watermelon, raw	4.1

 

Key References:

Krinsky NI. The antioxidant and biological properties of the carotenes. Ann NY Acad Sci 1998;854:443-7.
Kohlmeier L, Kark JD, Gomez-Gracia E, et al. Lycopene and myocardial infarction risk in the EURAMIC Study. Am J Epidemiol 1997;146:618-26.
Rao AV, Agarwal S. Role of antioxidant lycopene in cancer and heart disease. J Am Coll Nutr. 2000;19(5):563-9.
Weisburger JH. Lycopene and tomato products in health promotion. Exp Biol Med. 2002;227(10):924-7
Gann PH, Ma J, Giovannucci E, Willett W, et al. Lower prostate cancer risk in men with elevated plasma lycopene levels: results of a prospective analysis. Cancer Res 1999;59:1225-1230.
Kucuk O, Sarkar FH, Sakr W, et al. Phase II randomized clinical trial of lycopene supplementation before radical prostatectomy. Cancer Epidemiol Biomarkers Prev 2001;10:861-8.
Ansari MS, Gupta NP. A comparison of lycopene and orchidectomy vs orchidectomy alone in the management of advanced prostate cancer. BJU Int. 2003 Sep;92(4):375-8.
Argarwal S, Rao AV. Tomato lycopene and low density lipoprotein oxidation: a human dietary intervention study. Lipids 1998;33:981-4.

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Michael T. Murray, N.D., is widely regarded as one of world's leading authorities on natural medicine. A prolific author, Dr. Murray has written over 20 books on health and nutrition including the best-selling Encyclopedia of Natural Medicine and his latest book The Encyclopedia of Healing Foods. Dr. Murray is also Director of Product Development and Education for Natural Factors one of the leading manufacturers of natural products.