THURSDAY, March 15 (HealthDay News) -- Consuming the toxic metal cadmium in the foods you eat may raise your risk for breast cancer, a new Swedish study suggests.

Cadmium, which is found in many farm fertilizers, can make its way into soil and water, the researchers explained. Some of the main sources of cadmium in the diet are bread and other cereals, potatoes, root crops and vegetables. Once it enters the body, cadmium may mimic the effects of the female hormone estrogen, which can fuel the growth of certain breast cancers.

"Modern life has become increasingly dangerous for our breast health," said Dr. Marisa Weiss, director of breast radiation oncology and breast health outreach at Lankenau Medical Center in Wynnewood, Pa. "Now, there's cadmium hanging onto our carrots and whole grains, the very vegetables that are supposed to be good for us," she noted.

"To help our patients reduce their exposure to environmental chemicals (like cadmium), which might increase their risk for breast cancer, we have to partner with our farmers to make sure our foods are grown in healthy soil without chemically loaded fertilizers," said Weiss, who is also president and founder of Breastcancer.org. "Sticking to real, whole (unprocessed) foods remains a healthy strategy until we can be more sure of what's inside the package."

In the Swedish study, the researchers followed close to 56,000 women for more than 12 years. Women filled out food frequency questionnaires, which the researchers used to estimate how much cadmium they consumed in their diets. There were 2,112 breast cancer diagnoses during the follow-up period, including 1,626 estrogen receptor-positive and 290 estrogen receptor-negative cancers.

Women who had the highest amount of cadmium in their diets were 21 percent more likely to develop breast cancer than women who had the least amount of cadmium in their diets. This risk increased to 27 percent among women who were lean or normal-weight, the study showed. The risk was similar, 23 percent, for both estrogen receptor-positive and -negative tumors.

Those 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," study author Agneta Akesson, an associate professor at Karolinska Institute in Sweden, said in a news release from the American Association for Cancer Research. "It is, however, important that the exposure to cadmium from all food is low."

The findings are published in the March 15 issue of Cancer Research.

Johanna Lampe, a member of the public health sciences division at Fred Hutchinson Cancer Research Center in Seattle, said the new study adds to a growing body of research linking cadmium exposure to breast cancer risk. "It adds another grain of sand to the pile," she said. "We would benefit from more research in this area to understand these risks better."

The ideal study would use a more objective measure of cadmium exposure, such as cadmium levels in urine. "We could look at women years before they develop breast cancer and measure cadmium exposure at certain points in time," she explained.

In terms of lowering exposure to cadmium, Lampe said that smoking is the most important single source of cadmium exposure. "Not smoking is a good place to start," she noted.

Dr. Stephanie Bernik, chief of surgical oncology at Lenox Hill Hospital in New York City, said that it is too early to recommend making any dietary changes based on these findings. "We can't say we should limit intake of fiber and other things that contain cadmium yet," and some of the foods that contain cadmium are part of a healthy diet, Bernik stressed.

In the study, thinner women had a higher risk for breast cancer based on their exposure to cadmium. "Obesity overrides any effect that cadmium may have on breast cancer," Bernik said, adding that obesity is a greater risk factor for breast cancer than cadmium exposure, because "when people are overweight, they have more estrogen circulating in the body."

More information

Learn more about breast cancer risks and how to lower yours at Breastcancer.org.