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Selenium
Numerous studies suggest that an inverse association exists betwen selenium levles and cancer incidence. Asspciations appear to be particularly strong with cancers that are also associated with hgh-fat, low-fibre diets (ie breast, colon, prostate etc). The mechanism for selenium's rprtd protective effects is likely to be function in antioxidant synthesis.
Selenium may also act as an immune stimulant. Selenium deficiency stops the destruction of tumors brought about by macrophages, and inhibits the production of tumor necrosis factor-alpha in animals. Dietary supplementation with selenium produces the opposite effect.
Zinc
The effercts of zinc on cancer development and growth are not well established, although the negative effects of zinc deficiency on the immune system are clear. In an evaluation of 261 patients with breast cancer and 281 controls, the cancer patients had singularly higher mean zinc blood levels. The higher levels were thought to be due to a release of tissue zinc stores. The effect of the release on cancer growth is uncertain.
Calcium
Numerous animals studies indicatre that calcium may inhibit colon cancer. Human studies indicate that calcium may reversibly inhibit hyperproliferation of colon cells. Calcium is likely to reduce colon cancer risk by combining with fat in the stool, thereby reducing lipid damage.
Phytonutrients
Numerous non-nutrient dietary factors, such as those from the Allium species (onions and garlic) and cruciferous vegtables (cabbage, cauli and broccoli), may play key roles in preventing cancer.
A number of non-nutrient dietary factors may also be useful in treating cancer. These include certain phytoestrogens, phytosterols, saponins, flavonoids, protease inhibitors isoflvones and lignans. Some of the mor promising compounds include the phytoestrogen equo;, the flavonoids quercetin, (+)-cachetin and epigallocachetin 3-galate (EGOG), the isoflavone genistein and lignans obtained from flax seed. These compounds may act by way of a variety of mechanisms to inhibit cancer growth, such as by reducing oestrogen bioavailability, inhibiting mitosis, inhibiting invasion, inhibiting angiognesis and inducing differentiation.
Protease Inhibitors
Soya beans contain protease inhibitors and isoflavones, both of which have been reported to prevent cancer.
Epidemiological studies indicate that soybean consumption may be rsponsible for the desreadsed incidence of a number of cancers sn in Chinese and Japanese populations. For example, Japanese who consume miso soup daily have significantly reduced risk of cancers of all types, compared with those who consume miso less often. Asian women who consume soy products regularly have lower rates of breast cancer than American women, who do not consume soy. Colon cancer incidence is reduced by 50% in those subjects who consume miso soup.
Isoflavones
Isoflavones are flavonoid compounds found in a varity of legumes such as soy, and other plant sources such as red clover. The volume of isoflavone research has exploded recently, especially into the isoflavone genistein (derived from soy). See Soya - The Two-edged Sword on this site (opens in another window).
Genistein (an isoflavone derived from soybeans) has several characteristics that make it very promising as an anticancer agent. For example genistein -
- inhibits platelet aggregation
- induces apoptosis (suicide of neutrophils)
- inhibits production of leukotrienes (chemicals which cause asthma symptoms derived from the action of enzyme 5-lipoxygenase on arachidonic acid)
- inhibits angiognesis (the growth of new blood vessels)
- reduces the bioavailability of sex hormones
- induces differentiation (a maturing process during which a determined cell becomes a recognizable, specialized cell) in cancer cells
Many of these characteristics may be related to genistein's ability to inhibit the protein tyrosine kinase (modification). As for the growth of new blood vessels, in one study fractions of the urine of healthy subjects who consumed a plant-based diet indicated that the diet inhibited the proliferation of vascular endothelial cells and also inhibited angiognesis in vitro. The most potent fractions contained isoflavones, of which the most potent was genistein.
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