Agneta Akesson, an associate professor at Karolinska Institutet in Sweden, and colleagues traced 55,987 women for more than 12 years. They estimated the dietary cadmium exposure using a food frequency questionnaire.
Cadmium occurs at low concentrations in nature but there is a concern because contamination of farmland mainly due to atmospheric deposition and use of fertilizers leads to higher uptake in plants, Akesson said.
"Because of a high accumulation in agricultural crops, the main sources of dietary cadmium are bread and other cereals, potatoes, root crops and vegetables," Akesson said in a statement. "In general, these foods are also considered healthy."
During the follow-up period, researchers observed 2,112 incidences of breast cancer -- including 1,626 estrogen receptor-positive and 290 estrogen receptor-negative cases.
The study, published in Cancer Research, found a higher exposure to cadmium from the diet was linked with a 21 percent increase in breast cancer, but among lean and normal weight women, the increased risk was 27 percent.
Both estrogen receptor-positive and negative tumors had the same risk increase, at roughly 23 percent.
Akesson said 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.
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