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Lycopene and Cancer Prevention

Gillian Treadwell

Oct 24, 2008

 

In recent years there has been a surge in advertisements for lycopene in tomato-based products.  Heinz Ketchup packaging boasts that their product is a natural source of lycopene, a powerful antioxidant.  Many researchers have postulated that antioxidants are crucial in preventing cell damage by free radicals, and can be useful tools in preventing degenerative diseases associated with aging, including heart disease and cancer (Ames, Shigenaga, & Hegen, 1993).  It makes sense that regular intake of a powerful antioxidant would help prevent age related diseases, including cancer.  Does scientific research support that lycopene plays an important role in preventing and fighting cancer?

 

What is Lycopene?

 

 

 

Product

Lycopene
(mg /100 ga)

Serving
Size b

Lycopene
(mg /serving)

Tomato Juice

9.3

240 mL (1 cup)

22.9

Tomato Ketchup

17.0

15 mL (1 tbsp)

2.9

Spaghetti Sauce

16.0

125 g (1/2 cup)

20.0

Tomato Paste

29.3

30 g (2 tbsp)

8.8

Tomato Soup (Condensed)

10.9

245 g (1 cup prepared)

13.1

Tomato Sauce

15.9

60 g (1/4 cup)

9.6

Chili Sauce

13.0*

15 mL (1 tbsp)

2.2

Seafood Cocktail Sauce

12.2*

60 g (1/4 cup)

7.3

Watermelon

4.9

280 g
(~1/16 of a watermelon)

13.6

Pink Grapefruit

1.5

154 g (1/2 medium)

2.3

Raw Tomato

3.0

148 g (1 medium)

4.5

Lycopene is an open chain carotenoid found in guava, red grapefruit, and watermelon; however, it is most famous for its concentration in tomato-based food products.  Carotenoids are pigments found in the photosynthetic complexes of some plants, fungi, algae, and bacteria (Stahl & Seis, 1996).  They absorb blue light and reflect all other wavelengths of visible light, which results in their orange to red color.  There are more than six hundred known types of carotenoids, but lycopene has become famous for its activity as a powerful antioxidant and concentration in common food items.  

Lycopene is an unsaturated carbon chain, and in nature is found in both cis and trans isomers.  According to Rao and Agarawa , heat can cause trans to cis isomerization (1999).  This reaction changes lycopene into an isomer that is more easily absorbed and used by the body.  According to www.lycopene.org, because products like ketchup and tomato sauce are cooked and processed using heat, they contain a higher concentration of biologically useful lycopene than raw tomatoes. 

 

What are free radicals and antioxidants?

Free radicals are molecules containing highly reactive unpaired electrons.  Some common free radicals and free radical precursors within the human body include superoxide, hydrogen peroxide, and hydroxide radical (Ames, Shigenaga, & Hegen, 1993).  The body typically does a good job of either sequestering or neutralizing free radicals, but free radicals loose within the cell can cause damage to protein, DNA, and lipids.  Most free radical damage elements can either be repaired or remove from the body, but unrepaired damage accumulates with age and has been hypothesized to be the foremost cause of aging (Ames, Shigenaga, & Hegen, 1993).   When DNA damage accumulates, basic cellular functions can be impaired.  Some DNA mutations cause uncontrolled cell division, otherwise known as cancer

Antioxidants are compounds that neutralize free radicals and presumably reduce the rate of the accumulation of cell damage.  Some common types include vitamins C, A, E, and beta carotene. 

 

Health claims:

                According to information found on www.lycopene.org, increased levels of lycopene in the blood lead to fewer oxidized compounds within the cell.  The website also claims that a diet high in lycopene containing vegetables is associated with a lower incidence of  certain kinds of cancer.  It is important to keep in mind that this website was created by Heinz Foodservice, a company that, for obvious reasons, stands to gain a lot from the beneficial health claims made about lycopene. 

 

Studies:

In a study conducted by Tang, Jin, Zeng, and Wang, it was found that lycopene inhibited the growth rate of prostate cancer cells in vitro (2005).  The study tested the effect of culturing three types of human cancerous prostate cells in varying concentrations of lycopene.  The researchers found that for one type of cell, a lycopene concentration of 26.6 µmol/L reduced the rate of growth by 50%.  Similarly, the other two types of cells were observed to have a 50% reduction in growth rate at 40.3 µmol/L and 168.5 µmol/L.    

Sies and Stahl’s research of the health effects of lycopene led then to a study conducted in Italy (1996).  In this study, 2706 patients with cancer were matched with 2879 controls.  It was found that protection from all kinds of digestive tract cancers was associated with a diet rich in tomatoes.  However, the correlation does not necessarily point to causality.  A person consuming a diet rich in tomatoes may consume many fruits and vegetables in place of less healthy options, leading to a lower risk of cancer. 

Etminan, Takkouche, and Caamano-Isorna searched for studies in MEDLINE and EMBASE and statistically analyzed date from previous research (2004).  The researchers discovered that compared to nonfrequent users of tomato products, those who ate high amounts of raw tomato had a relative risk of developing prostate cancer of 0.89, with a 95% confidence interval of 0.8 – 1.0.  For those who consumed large amounts of cooked tomatoes, they found that the relative risk was 0.81, with a 95% confidence interval of 0.71 – 0.92.  The relative risk for those who ate one serving of raw tomato daily was 0.97, with a 95% confidence interval of 0.85 – 1.10.  The researchers concluded that tomato products may play a role in cancer prevention, but a large amount of tomato must be consumed daily to achieve even a small benefit.

The Health Professionals Follow-up Study (HPFS) is a prospective epidemiological study following about 47,000 men.  The men were studied from 1986 to 1992 and asked to fill out questionnaires periodically (Campbell et al., 2004).  Analysis of the data acquired showed that there was a 26% reduced rate of prostate cancer when the participant consumed 2-4 servings of raw tomatoes per week, when compared to those who ate none.  Men who ate 2-4 servings per week of cooked tomato products, such as tomato sauce, had a 35% reduced risk of developing prostate cancer.  Again, this study shows a correlation, but not necessarily a causal relationship. 

 

 

 

Conclusion: 

While it is very likely that lycopene plays an important role in cancer prevention, it is difficult to say with scientific certainty that this is the case.  The scientific evidence presented in the above cases isn’t overwhelmingly conclusive.  The studies that retrospectively analyze lycopene intake can only prove that there is a correlation between lycopene intake and reduced risk of cancer, not necessarily that the reduced risk of cancer is a result of the action of the lycopene.  The study performed in vitro would need to be performed in vivo before any broad conclusions about lycopene and prostate cancer in living humans could be made.

The FDA has rejected a lycopene manufacturer’s request to claim that lycopene can prevent cancer because the research has been inconclusive (FDA, 2007).  When such specific health claims are used to advertise, consumers become more focused on specific products than on striving for a healthy diet as a whole.  An all around healthy diet is one of the most important aspects of cancer prevention, not necessarily just one food product that acts as a magic bullet. 

That being said, no evidence was presented in the above studies that states that consumption of tomatoes can be deterimental to one’s health.  Tomatoes are an excellent source of many nutrients, including folate, vitamin C, carotenoids and polyphenols, which may also have cancer preventative effects (Campbell et al., 2004).  Although not a certainty, it is plausible that lycopene can help prevent certain kinds of cancer.  Including more tomatoes in your diet has the potential to have health benefits, and is very unlikely to do any harm whatsoever.   A diet high in fruits and vegetables, including tomatoes, has a variety of beneficial effects, and is very likely to reduce the risk of many types of cancer. 

 

References:

Ames, Bruce N.,  Shigenaga, Mark K. and Hagen, Tory M.  Oxidants, Antioxidants, and the Degenerative Diseases of Aging.   Proceedings of the National Academy of Sciences of the United States of America, Vol. 90, No. 17 (Sep. 1, 1993), pp. 7915-7922

Campbell, Jessica K;  Canene-Adams,  Kirstie;  Lindshield, Brian L;  Boileau, Thomas  et al. (2004). Tomato Phytochemicals and Prostate Cancer Risk1,2. The Journal of Nutrition: International Research Conference on Food, Nutrition, and..., 134(12S), 3486S-3492S.  Retrieved October 10, 2008, from Research Library Core database. (Document ID: 768198191).

 

Etminan, Mahyar, Takkouche, Bahi, Caamano-Isorna, Francisco.  The Role of Tomato Products and Lycopene in the Prevention of Prostate Cancer: A Meta-Analysis of Observational Studies. Cancer Epidemiol Biomarkers Prev 2004 13: 340-345

 

FDA Claims Lycopene Not Cancer-Protective. Medical News Today. July 27th, 2007. http://www.medicalnewstoday.com/articles/77958.php

Rao A.V., Agarwal S.  Role of lycopene as antioxidant carotenoid in the prevention of chronic diseases: A review (1999) Nutrition Research, 19 (2), pp. 305-323

 

Stahl, Wilhelm; Sies, Helmut.  Lycopene: A Biologically Important Carotenoid for Humans? Archives of Biochemistry and Biophysics.  1996 Vol. 336:1 pp. 1–9

 

Tang, Lili; Jin,Taiy; Zeng, Xiangbin Wang,;Jia-Sheng.  Lycopene Inhibits the Growth of Human Androgen-Independent Prostate Cancer Cells In Vitro and in BALB/c Nude Mice1. The Journal of Nutrition. Bethesda: Feb 2005. Vol. 135, Iss. 2; p. 287

 

www.lycopene.org

 

 

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