Recently, you may have heard the words chemoprevention, nutraceuticals, and phytochemicals in the media. What exactly do these terms mean? With the ever-increasing interest in improving our health, it is important to understand these words and understand their function in health care. The information presented here will provide a basis for deciphering the mixed messages that are being delivered in the media, conversations, research, and education.
Research has demonstrated that cancer is a largely avoidable disease. It is estimated that more than two-thirds of cancer may be prevented through lifestyle modification (1). Nearly one-third of these cancer occurrences can be attributed to diet alone, secondary to our American diet of high-fat, low-fiber content. Fruit and vegetable consumption have been consistently shown to reduce the risk of many cancers (2). A major prevention strategy has been the "5 A Day for Better Health" program sponsored by the National Cancer Institute (NCI), encouraging the public to include more fruits and vegetables in their diet.
The American Cancer Society has developed guidelines for nutrition and cancer prevention. These guidelines are similar to the Dietary Guidelines for Americans and include the following:
Consequently, even before these guidelines were developed, researchers began investigating several substances that have the potential to inhibit cancer tumor formation. This investigation evolved into what is called "chemoprevention" today. The "chemoprevention" strategy of preventing cancer was founded in the mid 1970s by Michael B. Sporn, an innovator in cancer prevention research (3). Successful trials involving chemopreventive agents and animals led scientists to design larger similar trials with humans. In fact, in 1995 the NCI alone sponsored more than 50 trials of 25 different compounds (4). These chemical compounds along with several others are currently being recognized for their potential to prevent and treat various types of cancer.
This fact sheet will explain the concept of chemoprevention, list agents used in chemoprevention, and describe benefits of chemoprevention in regard to cancer prevention and treatment.
| Current "Buzzwords" in Nutrition |
|---|
Chemoprevention -- Using one or several chemical compounds to prevent, |
Designer Food -- Processed foods that are supplemented with food |
Functional Food -- Any modified food or food ingredient that may provide |
Nutraceutical -- Specific chemical compounds in food, including vitamins |
Pharmafood -- Food or nutrient that claims medical or health benefits, |
Phytochemical -- Nonnutrient plant chemicals that contain protective, |
Chemoprevention is the attempt to use natural and synthetic compounds to intervene in the early stages of cancer, before invasive disease begins. This strategy is involved in the process of carcinogenesis -- the transformation of a normal cell into a cancer cell. Currently, the NCI has made chemoprevention research a top priority; more than 400 potential agents are currently under investigation (8).
Chemopreventive agents can act in two ways: they can prevent or stop genetic mutations that lead to cancer, and they can prevent or stop processes that lead to excessive replication of damaged cells.
Chemoprevention should not be confused with chemotherapy. Chemotherapy's aim is to kill cells, particularly cancer cells, in the hope of preventing further cancer progression. Chemoprevention, on the other hand, involves administering nontoxic agents to otherwise healthy individuals who may be at increased risk for cancer.
An agent must have minimal short-term and no known long-term toxicity. It must be highly effective, easy to administer, and be inexpensive (9). Food, a readily available item, contains several promising chemopreventive compounds such as certain vitamins, minerals, and phytochemicals. See the table below to find out more about these agents.
| Agent | Agent type | Cancer prevention/treatment |
|---|---|---|
| Vitamin A + other retinoids | vitamin | skin, head + neck, & lung |
| Vitamin C | vitamin | colon & stomach |
| Vitamin D | vitamin | colon |
| Vitamin E | vitamin | lung, head + neck, colon, & stomach |
| Folic Acid | vitamin | precancerous cells of the cervix |
| Selenium | mineral | skin |
| Calcium | mineral | colon |
| Beta-Carotene | phytochemical | lung, head + neck, colon & stomach |
| Monoterpenes | phytochemical | breast |
| Tamoxifen | drug | breast |
| Finasteride | drug | prostate |
| Oltipraz | drug | liver |
| NSAIDS (nonsteroidal anti-inflammatory drugs -- aspirin, buprofen) | drug | colon |
| Sunscreen | other | skin |
| Spirulina fusiformi | (blue-green algae) | other head + neck |
A potential chemopreventive agent goes through several phases before it can be administered to large numbers of people. These phases determine the chemopreventive agent's effectiveness, dose toxicity, and side effects. An agent starts in Phase I and continues to advance to Phase III as long as it is acceptable within specific guidelines. After an agent passes through Phase III, data is collected from the trial and then recommendations regarding the agent begin to be studied in further detail. It may take several years before an agent passes through all the phases and is recommended to individuals who have increased risk of developing cancer. The different phases are described in detail here:
Phase I: Involves 25-100 people, lasts less than one year, and studies dose toxicity and side effects of the agent in humans.
Phase II, IIb: Involves 100-1,000 people, lasts one to five years, studies the agent for effectiveness.
Phase III: Involves 1,000-10,000 people, lasts five to 10 years, determines the agent's effect on cancer incidence, and pays close attention to long-term side effects (10).
Studying the effect of the drug tamoxifen on the reduction of breast cancer rates in women at high risk or older than 35 years. Result(s): Study is on-going, but recent results indicate promising effects.
Studying the effect of the retinoid isotretinoin on secondary cancerous tumors in the head and neck of high-risk people who had been initially treated for head and neck cancer. Result(s): 83% decrease in secondary tumors of head and neck.
Studying the effect of four combinations of vitamins and minerals on reducing esophageal and stomach cancer in high-risk people. Result(s): 21% decrease in stomach cancer deaths for people taking beta-carotene, vitamin E, and selenium.
Studying the effect of the drug finasteride on prostate cancer risk in men ages 55 and over. Result(s): Results to be expected within four to five years.
The ultimate goal of chemoprevention is the reduction of cancer incidence. Approximately 550,000 people in the United States were expected to die of cancer in 1996 (12). In fact, 1.4 million new cancer cases occur each year in the United States. If chemoprevention can prevent one or even 1,000 occurrences of cancer without complications, it can be deemed successful. The individuals that are targeted include people with lifestyle risks such as smoking or a high-fat diet, people with a family history of cancer, people at high risk because of a precancerous condition, and people who have had cancer and are at risk for a second cancer.
Even though many chemopreventive agents are naturally found in food, they are administered at high doses that can possibly produce unfavorable side effects. Short- and long-term side effects of chemopreventive agents are unknown at this time.
Although most chemoprevention trials show promising results, there are a few that present possible detrimental effects. One study, the Alpha-Tocopherol, Beta-Carotene Lung Cancer Prevention Study, tested daily doses of alpha-tocopherol (vitamin E) or beta-carotene, or both, on reducing the rates of lung and other cancers in male smokers. One of the findings included an 18% increase in lung cancer in the beta-carotene group. This result stresses the importance of waiting for conclusive results and approved recommendations from the scientific world before making any lifestyle changes.
There is little evidence supporting widespread use of chemopreventive agents in the entire population. The evidence only supports risk reduction for those individuals at risk for cancer. At this time, the NCI does not recommend supplements of vitamins, minerals, or other agents for the prevention of cancer. It does recommend eating a well-balanced, low-fat diet including fruits, vegetables, and grains.
Chemoprevention is not simple, and successes may not come quickly. However, for individuals at high risk for cancer and possibly the general population in the future, chemoprevention has the potential of providing an important means for cancer risk reduction (13).
As with any health recommendation, it is advisable to consult your health-care provider before making any lifestyle changes. This fact sheet should not in any way replace the advice of your physician.
1. Oliveria, S. A. et al. 1997. The Role of Epidemiology in Cancer Prevention. The Soc for Exp Bio and Med 216:142-150.
2. Block, G. et al. 1992. Fruit, vegetables, and cancer prevention: A review of the epidemiologic evidence. Nutr Cancer 18:1-29.
3. Greenwald, P. 1996. Chemoprevention of Cancer. Scientific American. Sept. 96-99.
4. Swan, D., B. Ford. 1997. Chemoprevention of Cancer: Review of the Literature. ONF 24(4): 719-727.
5. Mirvish, S. S. et al. 1975. Induction of mouse lung adenomas by amines or ureas plus nitrite and by N-nitoso compounds: effect of ascorbate, gallic acid, thiocyanate, and caffeine. J Natl Cancer Inst 55:633-636.
6. Thomas, P. R., R. Earl, Eds. 1994. Opportunities in the Nutrition and Food Sciences, Research Challenges and the Next Generation of Investigators. National Academy Press.
7. Bloch, A. et al. 1995. Position of the American Dietetic Association: Phytochemicals and functional foods. JADA. 95:493-496.
8. Swan, D., B. Ford. 1997. Chemoprevention of Cancer: Review of the Literature. ONF 24(4): 719-727.
9. Swan, D., B. Ford. 1997. Chemoprevention of Cancer: Review of the Literature. ONF 24(4): 719-727.
10. Goodman, G. 1997. The Clinical Evaluation of Cancer Prevention Agents. The Soc for Exp Bio and Med 216:253-259.
11. Greenwald, P. 1996. Chemoprevention of Cancer. Scientific American. Sept. 96-99.
12. Wattenberg, L. 1997. An Overview of Chemoprevention: Current Status and Future Prospects. The Soc for Exp Bio and Med 216:133-141.
13. Wattenberg, L. 1997. An Overview of Chemoprevention: Current Status and Future Prospects. The Soc for Exp Bio and Med 216:133-141.
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