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Metals Metals are natural products of our earth. At very minute levels and through regular dietary intake, some of these metals are critical to our cells' abilities to function normally. But if we are exposed to metals in the air (from mining dust or cigarette smoke, for example) or in our water, these higher doses or heavy metals can cause serious health effects. Some of these metals have recently been shown to mimic estrogens, perhaps explaining why they may be associated with increases in breast cancer risk.

What are the chemicals that are causing concern and where are they found?

Many heavy metals are naturally occurring and are used in a variety of industrial settings. Metals cannot be created or destroyed, but can change form, altering their biological availability and toxicity. Metals used in industry many times wind up in the food supply, groundwater, drinking water, and soil. Metals are also found in many consumer products as well. These metals include copper, cobalt, nickel, lead, mercury, tin, chromium, cadmium, aluminum, vanadate (metal anion), antimony, barium, selenite, and arsinite.

Cadmium is a widely distributed metal used in manufacturing and present in a number of consumer products. It is used as a metal alloy, in paint, batteries (Ni-Cd), pigments, metal coatings, plastics, welding, and battery manufacture.

Aluminum is used in a wide range of products such as cooking utensils, containers, appliances, and building materials. It is also used in paints, fireworks, and in the production of glass, rubber, and ceramics. Aluminum is also found in consumer products such as antacids, astringents, buffered aspirin, food additives, and antiperspirants.

How do these chemicals enter the body?

Exposure to heavy metals can occur through a variety of pathways. Many metals enter the air from mining and industry, binding to particles in the air, and enabling the metals to travel long distances, where they can then be taken into the body by breathing the contaminated air. Metals can also enter the soil and water where they bind strongly to soil particles and dissolve in water, thus remaining in the environment. Exposure can then occur from drinking contaminated water. Also, fish, plants, and animals take up the heavy metals from their polluted surroundings. Human exposure can then occur when these animals and plants are eaten.

Cadmium also enters the body easily through first- and second- hand cigarette smoke. Aluminum exposure can occur from the daily use of consumer products such as antiperspirants, cooking utensils, and other medications including antacids, astringents, and buffered aspirin. When these products are used, aluminum is taken into the body by absorption through the skin or through ingestion.

What are the mechanisms by which these substances might increase the risk for breast cancer?

Cadmium and other heavy metals have been shown to be estrogenic, and have the ability to activate the estrogen receptor, similar to the effects of estradiol [Martin et al., 2003]. The expression of estrogen receptors is also affected and results in the levels of estrogen receptor being greatly reduced [Garcia-Morales et al., 1994] again mimicking the effects of natural estrogens. The regulation of expression and activity of estrogen receptor plays an essential role in the growth, differentiation, and prognosis of human breast cancer. Thus, the effects of the metals in living organisms have also been found to change the breast anatomy in specific ways, making it more susceptible to cancer, including an earlier onset of puberty, an increase in epithelial area, and an increase in the number of terminal end buds in the mammary gland [Johnson et al., 2003]. Aluminum has been found to interact with DNA, binding strongly to the phosphate backbone of the structure under neutral conditions [Zhang et al., 2002]. This suggests that aluminum could serve as a possible source of DNA damage, increasing the chances of DNA mistakes and promote the growth of the damaged cells. It has also been shown that aluminum can interfere with cell growth regulatory processes through many pathways, including altering gene expression [Darbre, 2003].