(ChemotherapyAdvisor) – Risk of breast cancer increases with increasing exposure to dietary cadmium, a toxic metal found in many fertilizers and a “ubiquitous food contaminant” that has features of an estrogen mimetic, a population-based prospective study published in the March 15 issue of Cancer Research has found.

“Because of a high accumulation in agricultural crops, the main sources of dietary cadmium are bread and other cereals, potatoes, root crops, and vegetables,” said Agneta Åkesson, PhD, associate professor at Karolinska Institutet in Sweden, where the study was conducted. “In general, these foods are also considered healthy.”

The investigators examined the association between dietary cadmium exposure at baseline in 1987 and risk of overall and estrogen receptor (ER)-positive or ER-negative breast cancer within a cohort of 55,987 postmenopausal women. Dietary cadmium exposure was estimated using a food frequency questionnaire. During an average follow-up of 12.2 years, 2,112 incident cases of invasive breast cancer were observed, 1,626 ER-positive and 290 ER-negative.

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“After adjusting for confounders, including consumption of whole grains and vegetables (which account for 40% of the dietary exposure, but also contain putative anticarcinogenic phytochemicals), dietary cadmium intake was positively associated with overall breast cancer tumors,” they wrote. Comparing the highest tertile with the lowest, the rate ratio (RR) was 1.21. Among lean and normal weight women, statistically significant associations were observed for all tumors (RR, 1.27) and for ER-positive tumors (RR, 1.25). Similar, but not statistically significant associations were found for ER-negative tumors (RR, 1.22).

Dr. Åkesson said that women who consumed higher amounts of whole grain and vegetables had a lower risk of breast cancer compared to women exposed to dietary cadmium through other foods. “It’s possible that this healthy diet to some extent can counteract the negative effect of cadmium, but our findings need to be confirmed with further studies,” she said. “It is, however, important that the exposure to cadmium from all food is low.”

“Overall, these results suggest a role for dietary cadmium in postmenopausal breast cancer development,” they concluded.