August 1, 2003. For the first time a study has found that the heavy metal cadmium mimics estrogen and damages estrogen-sensitive tissues in the breast and uterus and in unborn offspring.
Researchers at the Lombardi Cancer Center at Georgetown University studied cadmium and its ability to mimic estrogen's effects on the body. When exposed to low doses of cadmium, female rats show an increase in mammary gland density and uterine weight, and changes in the endometrial lining, all telltale developments in the early onset of breast cancer.
Additionally, when pregnant rats were exposed to the same low dose, their female offspring experienced earlier onset of puberty and mammary gland development. Early onset of puberty can increase a woman's chance for getting cancer by fifty percent.
"We never expected to see this strong a relationship, given how different the cadmium and estrogen compounds are," said Mary Beth Martin, Ph.D., associate professor of oncology at Georgetown University Medical Center. "Cadmium's ability to functionally mimic estrogen and its affect on cell growth is quite remarkable. What we saw suggests a direct link between low dose cadmium exposure and increased risk for breast cancer."
With 15,000 tons of cadmium produced each year for batteries, alloys, fertilizers and pigments, this heavy metal is one of the commonest environmental pollutants. Chronic exposure can cause kidney damage and bone disease. In occupational health studies, cadmium has been linked not only to breast cancer but also to lung cancer and prostate cancer.
Cadmium is present in cigarette smoke. A study published this month found that heavy smoking doubles the risk of aggressive prostate cancer. The authors cite as one likely factor, increased exposure to cadmium.
Some scientists, says Dr. Martin, suggest that environmental contaminants that mimic the effects of estrogen "contribute to disruption of the reproductive systems of animals in the wild, and to the high incidence of hormone-related cancers and diseases in Western populations." Previous studies have shown that cadmium acts like steroidal estrogens in breast cancer cells as a result of its ability to form a high-affinity complex with the hormone binding domain of the estrogen receptor.
Martin says the study's results provide "solid evidence that cadmium has estrogenic effects in the whole animal." These are not isolated results but"follow up on earlier studies reporting that cadmium and other heavy metals such as nickel interact with the estrogen receptor." Recent laboratory studies on yeast showed that cadmium damaged the ability of DNA to repair itself (Jin et al., Nat. Genet. 34, 326-329; 2003).
The latest studies found that cadmium set off potent estrogenic responses in rats at doses close to the cut off level recommended by the World Health Organization (7 micrograms per kilogram per week).
In addition to pinpointing another mechanism for some of cadmium's effects, the new data could call into question current regulatory standards for cadmium exposure.
Nature Medicine, August 2003 Volume 9 Number 8 pp 1081 - 1084. Cadmium mimics the in vivo effects of estrogen in the uterus and mammary gland Michael D Johnson, Nicholas Kenney.... & Mary Beth Martin.
Cadmium, Contained in Street De-Icer Magnesium Chloride, Linked to Human Cancer by Sterling Greenwood (Aug 2003)