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Phytochemicals for Cancer Prevention

© David Olle

Phytochemicals are naturally occurring biochemicals that plants developed in order to protect themselves from oxidation, insects, disease organisms and other hazards in their environment. These chemicals give plants their characteristic color, flavor, smell and texture. They are found in abundance in frequently consumed foods such as fruits, vegetables, grains, legumes, and seeds.

Although phytochemicals are not nutrients in the traditional sense, such as vitamins and minerals, researchers are actively studying their health benefits to consumers. However, to date few clinical trials have been conducted, and their claimed benefits are largely based on animal or epidemiological studies. Epidemiological or population studies try to equate the diets consumed in a particular region with incidence of particular diseases. Since controlled clinical trials try to determine cause and effect of a single drug or chemical, it can be a daunting task in the case of phytochemicals. Literally thousands of phytochemicals have been found in foods, and there is evidence that in some cases at least, their protective effect may result from acting in concert.

Are phytochemical drugs or food supplements on the horizon?

Phytochemicals have received top billing in the popular press for many years. In a recent conference sponsored by the American Institute for Cancer Research, 1 a question was posed- "should companies be allowed to synthesize phytochemicals to fortify foods or to offer in pill form?" The consensus of researchers present was "not in the foreseeable future." There is simply not enough known about safety or effectiveness of individual phytochemicals to recommend such a move. Instead, initiatives by the National Cancer Institute, the European Prospective Investigation of Cancer and Nutrition, and the World Health Organization to promote increased consumption of fruits and vegetables are encouraged. In order to be effective, consumption of these foods has to be a long-term process over many years, since the concentration of phytochemicals in these foods is relatively low.

How do phytochemicals help to prevent cancer?

Carcinogenesis is a multistep process consisting of tumor initiation, promotion, and progression. 3 Phytochemicals can act at any of the stages. Initiation is the conversion of a normal cell to a cancer cell after exposure or uptake of a carcinogen and its interaction with the cellular DNA. Cancer-blocking agents prevent carcinogens from reaching the cell, or prevent the carcinogen from interacting with cellular components. Examples of phytochemicals that block initiation include ellagic acid, indole-3-carbinol, sulphoraphane, and flavonoids.

Cancer-suppressing agents, on the other hand, block the promotion stage, which is the slow multiplication of cancer cells to pre-neoplastic cells, or to the progression stage, which is the conversion to neoplastic cells that can invade tissues and metastasize (spread). Examples of cancer-suppressing phytochemicals include β-carotene, curcumin, epigallocatechin gallate, genistein, resveratrol, gingerol, and capsaicin. Most of these cancer-suppressing phytochemicals act on signaling molecules that have been abnormally activated or silenced. These signaling molecules, which are kinase enzymes, are responsible for the activation of genes that regulate cell growth, differentiation, and apoptosis (cell death). Cancer progresses when these processes are unregulated.