Fruits and vegetables contain many phytochemicals that have biological effects in humans. Phenolics, glucosinolates, terpenoids, carotenoids and phytoestrogens have all been identified as having possible protective effects against disease. Grapes are a particularly good source of a number of phytonutrients including tannins, anthocyanins, proanthocyanidins, stilbenes and flavonols, which are thought to confer protective effects against certain diseases. Raisins, grape juice, wine and supplemental grape seed extract all contain some of these chemicals in varying amounts. The flesh, seeds and skins of grapes are all abundant sources of polyphenols with slightly differing profiles. Research is accumulating to suggest that grapes and grape products are able to protect against cancer in those who ingest them regularly. It is thought that some of the polyphenols in grapes have specific activity against cancerous cells which makes them potent chemoprotective agents.
In animal studies grape seed extract has shown promising results against cancer. For example, mice fed grape seed extract are protected from skin cancer induced by both UVB radiation and by carcinogens such as 12-O-tetradecacanoylphorbol 13-acetate. Grape seed extract has also shown to be effective against breast, prostate and colorectal cell lines. The exact mechanism of protection is not fully understood, but evidence suggest that grape polyphenols are able to induce programmed cell death (apoptosis), decrease angiogenesis and alter DNA turnover enzymes in cancerous cells. The skin of grapes is rich in anthocyanins which have known anticancer effects in vitro. Also in the skin is the stilbene resveratrol which has demonstrated potent anticancer effects in a number of animal and cell culture models. A metabolite of resveratrol, piceatannol, has also been shown to have anti cancer effects.
Although the chemicals present in grapes show promise as chemoprotective agents it is worth considering that the effects of whole grapes, wine, raisins or grape juice may be greater than the individual nutrients used in cell and animal studies. While it is important to use isolated chemicals in research to understand individual effects, foods are complex mixtures of chemicals. For example, red wine has a complex chemistry that is not fully understood, and chemical interaction occur during the manufacturing process, such that the age of the wine, the grape used, the growing conditions and the alcohol content may all effect the biological effects seen in humans following consumption. For this reason it is recommended that to attain the best chemoprotective effects from grapes, a variety of different grape products are consumed in order to maximise possible benefits.
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