March 15, 2012 -- Exposure to high levels of dietary cadmium may boost the risk of breast cancer, according to new research.
Cadmium is a metal commonly found in the environment. It is also found in many farm fertilizers. From fertilizers, it can work its way into food. It is found in breads, cereals, potatoes, root crops, and vegetables.
"It's been known for some time that cadmium is toxic and, in certain forms, carcinogenic," says Bettina Julin, a doctoral student at the Karolinska Institutet in Stockholm.
The metal can have estrogen-like properties, and estrogen can fuel breast cancer growth.
In the new study, Julin and her colleagues followed nearly 56,000 Swedish women for more than 12 years. Those who had the highest level of exposure to cadmium from their diets had a 21% increased risk of breast cancer.
It’s important to note that the researchers found a link between cadmium and breast cancer risk, but that does not prove cause and effect.
The findings are not a reason to avoid vegetables and whole grains, the researchers say. In fact, they found that women in the study who ate a lot of whole grains and vegetables had a lower risk of breast cancer compared to women who were exposed to the cadmium through other foods.
The grains and vegetables may protect against breast cancer because of their antioxidant properties and in other ways, the researchers say.
The study is published in Cancer Research.
Cadmium and Breast Cancer Risk: Study Details
In the past, cadmium has been linked with lung cancer in workers exposed to it, Julin tells WebMD in an email.
The possible link with breast cancer is newer, she says. It has surfaced in the last eight years as researchers found in animal research that cadmium has estrogen-like effects. Excess estrogen can raise breast cancer risk in women past menopause, she says.
For the new study, the researchers used information from the Swedish Mammography Cohort, which was established in 1987 to 1990. The women answered questioned about diet and gave other information.
During the 12 years of follow-up, there were 2,112 cases of breast cancer.
Most (1,625) were cancers known as estrogen-receptor positive. These cancers require estrogen to grow.
The researchers divided the women into three groups, from lowest to highest dietary intakes of cadmium.
The lowest group took in less than 13 micrograms a day. The middle group took in about 13 to 16. The highest group took in more than 16 micrograms a day.
Experts recommend different ''safe'' levels. For instance, the World Health Organization recommends 25 micrograms per kilogram of body weight per month. For a 120-pound woman, that would mean about 45 micrograms a day.
The risk was higher in normal weight or lean women than in overweight women, the researchers found. While the overall risk from high cadmium levels was 21%, it was 27% for the normal weight and lean women.
The link between cadmium and breast cancer risk was stronger, not surprisingly, for estrogen-receptor positive cancer. Estrogen-receptor positive or ER-positive cancers are fueled by estrogen. The link between cadmium and breast cancer risk for ER-negative cancers was too slight to be significant from a statistical point of view.
Vegetables, Whole Grains May Offset Risk
Women who ate diets high in whole grains and vegetables appeared to be protected, Julin found.
It's not certain why. It could be due to the antioxidant properties of the foods, the researchers say.
The study was funded by the Swedish Cancer Society, the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning, and the Swedish Research Council/Research Infrastructures.
Cadmium and Breast Cancer Risk: Perspective
"This is a very solid study that is likely to be influential in getting cadmium classified as either a breast carcinogen or a breast tumor promoter," says Kenneth Portier, PhD, managing director of the Statistics & Evaluation Center for the American Cancer Society.
He reviewed the findings for WebMD.
The new study ties in what researchers know about cadmium exposure from laboratory and animal studies and extends it to its effect in women, he says.
Exactly why cadmium is linked to risk is not clear. Portier suspects it is the estrogen-like properties of the cadmium. "Recent research has demonstrated that cadmium can operate like estrogen in the body, and we know from other data that estrogen promotes cancer growth."
These effects would be most evident in women past menopause, he says. That is because they have less estrogen. As a result, they are sensitive to increases in estrogen from outside the body.
"In women who have gone through menopause, you have to be concerned about anything that may increase estrogen levels -- including dietary sources," he tells WebMD.
However, he urges women to put the risk in perspective. Many other factors affect breast cancer risk, he says. Among them:
- Family history of breast cancer
- Excess alcohol intake
- Inactive lifestyle
More research is needed, he tells WebMD, to figure out how to reduce possible risk due to cadmium.