- Nonprovitamin A carotenoid
For Patients & Caregivers
How It Works
Diets that contain many fruits and vegetables rich in carotenoids like lycopene can help prevent some types of cancers and heart problems. However, not enough research has been done to say whether lycopene supplements have the same effect.
Lycopene is a natural pigment that is produced by plants and microorganisms. Laboratory experiments with lycopene confirm that it acts as an antioxidant and affects the way cells grow and communicate with each other, although it is not as potent as beta-carotene. Scientists have proposed several different mechanisms by which lycopene might fight cancer. These include stopping cancer cell growth, preventing DNA damage, and enhancing enzymes that break down cancer-causing products. Studies in healthy elderly patients suggest that consumption of lycopene or tomato juice does not stimulate the immune system. In general, diets rich in carotenoids like lycopene have been associated with decreased risk of macular degeneration, cataracts, some types of cancers, and some heart problems.
- To prevent and treat cancer
Lycopene is an antioxidant. One clinical trial suggested that preventative use of lycopene supplements reduces the spread of localized prostate cancer, but there is no other proof from clinical trials that lycopene can treat cancer. Diets rich in carotenoids like lycopene are generally associated with a decreased risk of certain types of cancers.
- To treat asthma
One clinical trial showed that daily lycopene supplementation protected against exercise-induced asthma, but no additional studies have been performed to confirm this.
- As an antioxidant
Laboratory studies support this use.
- To treat heart disease
Diets rich in carotenoids like lycopene are generally associated with a decreased risk of some cardiovascular events. However, there is no proof that lycopene supplements have the same effect.
- To prevent and treat macular degeneration
Diets rich in carotenoids like lycopene are generally associated with a decreased risk of macular degeneration. However, there is no proof that lycopene supplements have the same effect.
For Healthcare Professionals
A natural pigment synthesized by plants and microorganisms, lycopene is used primarily as an antioxidant and also to prevent and treat cancer, heart disease, and macular degeneration. Lycopene is classified as a non-provitamin A carotenoid, other examples being lutein and zeaxanthin. Alpha-carotene, beta-carotene, and beta-cryptoxanthin are classified as provitamin A carotenoids because they can be converted into retinol.
Small clinical trials suggest possible benefit against exercise-induced asthma (1) and benign prostatic hyperplasia (BPH) (2). However, no optimal dosage has been established. Data from observational studies indicate an inverse association of lycopene consumption with risk of developing cardiovascular disease (CVD) (26); with a randomized study reporting improvements in endothelial function in CVD patients, but not in healthy volunteers (27).
Lycopene was also shown to enhance antitumor efficacy of docetaxel against prostate cancer in animal models (22). And epidemiologic studies suggest an inverse relationship between lycopene consumption and risk of cancer (3), particularly lung (4), stomach (5), prostate (6), estrogen receptor (ER) and progesterone receptor (PR)-positive breast cancer (7). A consistent association between lycopene consumption and endometrial cancer risk has yet to be reported (8) (9).
However, clinical data on the effects of lycopene supplementation for prevention of prostate cancer remain inconclusive. Whereas low intake of tomato sauce is thought to be associated with advanced prostate cancer in patients with low-grade cancer at diagnosis (10), data from other studies indicate that lycopene or tomato-based regimens do not prevent prostate cancer (11) (23) (31).
In men with high grade prostatic intraepithelial neoplasia (PIN), a lycopene-rich extract did not confer any benefits (32); and high doses of lycopene, green tea catechins and selenium were actually associated with higher incidence of prostate cancer (28). Also, variable results were reported for lycopene supplementation in prostate cancer patients (12). Further studies are needed to resolve this ambiguity.
Quality control is a concern as shown by an analysis of six commercially available brands which revealed that lycopene content varied from the labeled dosage by as much as 43% (14).
Mechanism of Action
Lycopene is a natural pigment synthesized by plants and microorganisms. Referred to as a nonprovitamin A carotenoid, it is not known to have any vitamin A activity. Biological actions include antioxidant activity via singlet oxygen quenching and peroxyl radical scavenging, induction of cell to cell communication, and growth control, although this appears to occur with less efficiency than with beta-carotene (15). Preventive consumption of lycopene was shown to attenuate the effects of acetaminophen-induced liver injury in a murine model (29).
Proposed mechanisms of cancer preventive effects include inhibition of cancer growth, induction of differentiation by modulation of cell cycle regulatory proteins, alterations in insulin-like growth factor-1 (16) or vascular endothelial growth factor (17) levels, prevention of oxidative DNA damage, and possible enhancement of carcinogen metabolizing enzymes (18). The anti-metastatic action of lycopene was reported, in human liver adenocarcinoma cell model, to be via down-regulation of NADPH oxidase 4 (NOX4), which produces reactive oxygen species (30).
Other possible actions for all carotenoids include immune enhancement, inhibition of mutagenesis and transformation, and inhibition of premalignant lesions. Carotenoids have also been associated with decreased risk of macular degeneration and cataracts, decreased risk for some types of cancers, and decreased risk of some cardiovascular events (19).
- A possible interaction between lycopene and alcohol consumption was demonstrated in animal model, indicating that cytochrome P450 (CYP) 2E1 expression is induced by high doses of lycopene plus alcohol (13).