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.
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.
