NewScientist.com news service
Cadmium is astonishingly good at mimicking the effects of the female sex hormone estrogen, new research on rats has revealed. The discovery raises concerns that the metal, and others like it, could increase the risk of illnesses like breast cancer in people.
Cadmium is widely used in batteries, and is present in cigarette smoke and sewage sludge spread on agricultural land. It is best known for obvious toxic effects on the liver and kidneys.
But new research by Mary Beth Martin's team at Georgetown University in Washington DC shows that, at much lower doses, cadmium can cause very similar effects as estrogen.
Martin gave cadmium to female rats whose ovaries had been removed, so they could not make estrogen themselves. The animals received doses comparable to the level set by the World Health Organization as a tolerable weekly intake for people. The results were unexpectedly striking, with the effects of the cadmium appearing almost identical to those of estrogen.
Rats given cadmium rapidly developed heavier wombs, denser mammary glands and thicker womb linings - just as they did when given estrogen itself. They also began to make milk, and two genes usually activated by estrogen were switched on.
And when Martin's team gave cadmium to pregnant rats, their female offspring went through puberty sooner and developed denser mammary gland tissue, again matching the effects of estrogen.
Denser tissue in mammary glands is associated with a higher risk of breast cancer, and Martin's team is now studying this possibility. But she notes that more work needs to be done before the implications for people become clear: "We have to look closely at human exposure."
The main dietary sources of cadmium are wheat, grain and other cereals, potatoes and rice. Limits for the safe consumption of food ingredients are set by a joint expert committee of the WHO and the Food and Agriculture Organization.
This met in June and re-adopted the existing limit for cadmium, before the Georgetown team's data was available to them. But the limit is unlikely to be reconsidered in the near future, says a WHO spokesman.
Journal reference: /Nature Medicine/ (DOI: 10.1038/nm902