Burning fossil fuels and using chemical fertilizers are creating a food system laced with a toxic heavy metal.

We've all heard that mammograms can help detect the early stages of breast cancer, and that being obese or regularly eating red or processed meats are some of the causes of breast cancer. But what about actually preventing it in the first place? Scientists have clearly shown that exercising regularly and maintaining a healthy body weight are crucial to slashing your risk, but a new study suggests that doing your best to avoid cadmium, a heavy-metal contaminant detected in the food supply, may also help protect women.

Looking at data from more than 55,000 women, Swedish researchers investigated dietary habits and applied dietary cadmium data to come up with a calculation of cadmium exposure in the women's diets. During the next 12 years, researchers noted about 2,100 cases of breast cancer cases occurring in postmenopausal women. They split breast cancer cases into three groups based on the amount of cadmium the women were exposed to through food. The women with the highest dietary exposures of cadmium saw a 21 percent increase in breast cancer risk compared to the lowest levels of exposure.

Women who ate the most whole grains and vegetables were the least likely to develop breast cancer, compared to the women who had been exposed to cadmium through other sorts of food. Interestingly, bread and vegetables are also the most common sources of dietary cadmium. "We certainly cannot advise women against eating a certain kind of food; indeed, it seems as if whole grain products and vegetables even provide a degree of protection against cancer," explains lead investigator Agneta Åkesson, assistant profesor at Karolinska Institute of Environmental Medicine.

The study was published Thursday in the journal Cancer Research.

According to United States Geological Services data, about 90 percent of the phosphate rock that's mined is used to produce chemical fertilizers, and this rock is often contaminated with naturally-occurring cadmium. The cadmium-laced fertilizers are then used to grow food crops for people or animals. Cadmium also winds up in the atmosphere from the burning of natural gas, coal, oil, and wood. Facilities that incinerate medical waste, sewage sludge, and municipal waste also emit cadmium into the air, where it can come back in the form of tainted rain, according to the Environmental Protection Agency.

"Cadmium ends up on farmland not only by the use of fertilizers, but also through atmospheric deposition of emissions from various industries," explains Bettina Julin, doctoral student at Karolinska Institutet's Institute of Environmental Medicine.

"Cadmium can travel long distances in the atmosphere. From agricultural soil, it accumulates in crops."

Here's how to help protect yourself from cadmium in food:

• Definitely stop smoking. Tobacco leaves are particularly good at absorbing cadmium, and half of a smoker's cadmium exposure from cigarettes comes from the actual smoke, according to Julin.

• Limit cadmium-rich food consumption. Certain foods could contain higher levels of cadmium, including crabs and mussels, and organ meats like liver and kidneys, Julin adds.

• Support more sustainable farming. While it's impossible for any type of farmer to avoid cadmium that comes back to the soil in the form of rain, by supporting farmers who don't use chemical fertilizers, you can cut back greatly on the amount of cadmium in the soil. And remember, continue to eat your veggies! In this study, people who ate the most vegetables were best protected from breast cancer. Julin adds, "We also must remember that cadmium concentrations in our food are generally quite low, and that there are several other scientifically established causes of breast cancer."