Carotenoids and cancer prevention
Carotenoids are natural pigments found in various fruits and vegetables, prominently featuring yellow, orange, and red hues, as well as in dark green leafy vegetables. Known for their antioxidant properties, carotenoids may play a significant role in cancer prevention by neutralizing free radicals—unstable molecules that can damage cellular components and lead to cancer. Research suggests that dietary intake of carotenoids may reduce the risks of several cancers, including those of the prostate, breast, lung, and colon, among others. However, there is a cautionary note regarding carotenoid supplements; studies indicate that taking carotenoids in pill form, particularly beta-carotene, may increase cancer risks in smokers or former smokers. The exact mechanisms by which carotenoids affect cancer development remain unclear, though they are thought to inhibit cancer cell proliferation and activate detoxifying enzymes. While many studies show a beneficial relationship between carotenoid levels and cancer incidence, some data indicate potential risks associated with high concentrations from supplements. Overall, consuming carotenoids through a balanced diet of fruits and vegetables is generally considered safe and beneficial.
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Carotenoids and cancer prevention
ALSO KNOWN AS: Carotenes (alpha-carotene, beta-carotene)
DEFINITION: Carotenoids are chemical substances found in yellow, orange, and red fruits and dark green, leafy vegetables. They are rich in antioxidants, and some studies suggest that including carotenoids in diets sharply reduces the risks of various cancers. Other studies warn that they may promote cancer when taken in pill or capsule form, especially in smokers or former smokers.
Cancers treated or prevented: May reduce risk of prostate, breast, lung, cervical, colon, stomach, rectal, ovarian, oral, pharyngeal, bladder, and other cancers
Delivery routes: Oral in diet, tablet, or capsule
How these compounds work: Carotenoids are chemicals produced by plants best known for their reddish and yellowish colors, as in the reds of a tomato or carrot. Carotenoids reduce the risk and incidence of cancer by acting as antioxidants, binding with and thereby reducing the amount of free radicals in the human body. Free radicals (which act as oxidants) are unstable molecules that lack a sufficient number of electrons. In their quest to become stable, they can wreak havoc on genetic material and proteins, disrupting cell molecules and chemical processes and making cells more susceptible to cancer. Antioxidants eliminate many of these cell-harming free radicals, in theory reducing the predisposition of cells to become cancerous. Studies have also suggested that carotenoids in the diet can inhibit cancer development by stimulating the manufacture of detoxifying enzymes and inhibiting the proliferation of cancer cells by regulating communication between cancer cells.
The mechanism by which carotenoids may affect or prevent cancerous cells is unknown. Lycopene and beta-carotene are the two most widely studied carotenoids, though at least six hundred known carotenoids exist. Researchers have shown in the laboratory that small concentrations of alpha- or beta-carotene severely hindered the growth and spread of neuroblastoma cells. The N-myc gene exists in all cells and codes for proteins stimulating cell growth. Usually, this gene is dormant unless the cell becomes damaged or receives signals to activate cellular growth. Carotenoids inhibit this gene activity, causing a decrease in activation or complete inactivation of this gene in cancerous cells.
Some but not all studies show an inverse relationship between serum levels of carotenoids and cancer incidence, while others show no affiliation. Still others show high levels of certain carotenoids, such as beta-carotene, may increase the risk of certain cancers. Most, however, agree that the antioxidant role of carotenoids reduces the concentration of harmful oxidants.
Side effects: Consumption of large amounts of beta-carotene via dietary supplements may increase the risk of lung cancer, especially in smokers. As stated in the Wellness Guide to Dietary Supplements (produced by the online Berkeley Wellness Letter):
Don’t assume that beta carotene or other antioxidants in supplement form are beneficial, or even harmless. Don’t take beta carotene pills, particularly if you’ve ever been a smoker. Beta carotene is plentiful in vegetables and fruits, and is safe and beneficial when consumed from such foods.
Small amounts of carotenoids have been associated with beneficial effects like antioxidant activity, immune modulation, angiogenesis inhibition, and cell cycle regulation. Large amounts have, conversely, been associated with such detrimental effects as prooxidant activity (when other factors such as smoking are introduced), enhanced carcinogen binding, and oxidative damage to DNA.
Bibliography
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"Antioxidants and Cancer Prevention." National Cancer Institute, www.cancer.gov/about-cancer/causes-prevention/risk/diet/antioxidants-fact-sheet. Accessed 20 July 2024.
"Eat the Rainbow: The Health Benefits of Carotenoids." Cleveland Clinic, 12 July 2023, health.clevelandclinic.org/carotenoids. Accessed 20 July 2024.
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Tanaka, Takuji, et al. "Cancer Chemoprevention by Carotenoids." Carotenoids. Spec. issue of Molecules, vol. 17, no. 3, 2012, pp. 3202–42.
Wang, Yan, and Xiang-Dong Wang. "β-Carotene and Other Carotenoids in Cancer Prevention." Vegetables, Whole Grains, and Their Derivatives in Cancer Prevention. Vol. 2 of Diet and Cancer, edited by Marja Mutanen and Anne-Maria Pajari, Springer Science, 2011, pp. 67–89.