In a finding that strengthens the link between environmental pollutants and rising rates of breast cancer, new research finds that women whose diets contain higher levels of cadmium are at greater risk of developing breast cancer than those who ingest less of the industrial chemical in their food.
Cadmium, a heavy metal long identified as a carcinogen, leaches into crops from fertilizers and when rainfall or sewage sludge deposit it onto farmland. Whole grains, potatoes, other vegetables and shellfish are key dietary sources of cadmium, which also becomes airborne as a pollutant when fossil fuels are burned, and is likely inhaled as well as ingested.
The new study, published by the American Assn. for Cancer Research and released Thursday, found that among 55,987 post-menopausal women, the one-third with the highest cadmium intakes were 21% more likely to develop breast cancer than the one-third with the lowest intakes.
Among obese women, the study found no increase in breast cancer rates with higher cadmium exposures.
The study offers new evidence in a large human population that environmental chemicals that mimic the effects of the female hormone estrogen may contribute to women's risk of certain cancers, including endometrial and breast cancers.
The finding comes just three months after the Institute of Medicine, a prestigious body of independent biomedical researchers, concluded that a host of other factors most within a woman's power to control, such as obesity and hormone-replacement medication were the most important sources of breast cancer risk.
The panel of experts had called it "biologically plausible" that estrogen-like pollutants promote breast cancers, but noted that evidence that they contribute significantly was inconclusive. By contrast, studies in human populations strongly point to fattening foods, hormone-replacement drugs, alcohol and cigarettes as having roles in boosting a woman's breast cancer risk.
Even this study, while showing a correlation, did not prove cause and effect, experts noted.
UC Davis epidemiologist Irva Hertz-Picciotto, chairwoman of the Institute of Medicine panel that issued its findings in December, said the study "does not move us beyond" the panel's overall conclusions.
"At this point, we have not identified the major drivers of the increase in breast cancer," Hertz-Picciotto said. If cadmium pollution truly turns out to be a cause, she added, "it's probably a small part" of a very large picture.
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Cadmium in diet is linked to higher breast cancer risk
