The toxic heavy metal Cadmium is associated with increased breast cancer risk. Unlike some other heavy metals such as copper, iron and zinc, cadmium has no beneficial role in maintaining health and is not essential to human life. Numerous studies have demonstrated that cadmium interacts with breast cancer cells in ways that promote their growth and proliferation.

Cadmium is a heavy metal with industrial uses

Cadmium has toxic properties at relatively low concentrations. It accumulates in tissues since the body has no efficient mechanism for excreting it. Cadmium itself is not mined; it is a byproduct of smelting of other metals such as zinc, lead, and copper. However, cadmium has wide industrial uses, including in soldering and metal plating, the manufacture of alloys, plastics, and pigments, and the stabilization of phosphate fertilizers, as well as a component of batteries and electrical conductors.

Cadmium promotes breast cancer in cells

Cadmium is a metalloestrogen, a type of inorganic xenoestrogen that can affect the gene expression of cells with estrogen receptors. As such, cadmium functions as an endocrine disruptor, stimulating estrogen receptor activity. It has also been shown to promote uterine and mammary gland growth in mice.
Cadmium influences gene expression, modifying signaling in both normal and cancerous breast cells. Exposure to cadmium leads to reduced DNA repair capacity and genomic instability. The increased proliferation of cells with genomic instability is one possible viable mechanism for cadmium-induced cancer. Long-term exposure to cadmium in normal (MCF-10A) breast cells has been shown to increase colony formation and invasion, both typical of cancer cells.

Cadmium may reduce sensitivity to breast cancer treatment

Cadmium exposure has been reported to decrease the sensitivity of breast cancer cells to tamoxifen. Cadmium has also been found to modify the cell cycle, suppress apoptosis (programmed cell death), and alter the expression of various genes in ways that reduce the treatment effectiveness of 5-Fluorouracil (5-FU) chemotherapy in hormone receptor positive (ER+/PR+) breast cancer cells.

Human studies show link between cadmium and breast cancer risk

While not all studies are in agreement, there is ample evidence that cadmium promotes breast cancer in women:
  • A 2022 U.S. study reported that breast cancer patients had significantly higher urinary concentrations of lead and cadmium. However, after adjusting for all the covariates included in the study, only urinary lead was shown to be significantly associated with increased breast cancer.
  • An Iranian study reported that the level of cadmium was significantly elevated in cancerous breast tissue compared to breast tissue of healthy women.
  • A Japanese study found that women in the highest third of urinary cadmium levels had more than six times the risk of breast cancer compared to those in the lowest third. Urinary cadmium is a measure of exposure to cadmium over the prior 20 to 30 years. Japanese women have potentially high cadmium exposure through their rice and seafood consumption. The risk of breast cancer increased with increasing levels of cadmium.
  • A large Swedish prospective study reported that women in the highest third of cadmium intake had 21% higher risk of breast cancer than women in the lowest intake. The risk was highest among slender and normal weight women with high intake, for whom it was 27% higher. The risk was also higher for ER+ tumors than for ER- tumors (for which the elevated risk did not reach statistical significance). The risk of breast cancer was found to decline with increasing consumption of whole grains/vegetables within each level of cadmium exposure, suggesting that such consumption is protective.
  • A study that measured urinary cadmium levels of women living on Long Island, New York (a region with a high rate of breast cancer) and in a representative sample of the general U.S. population reported that both groups of women had increasing likelihood of breast cancer with increasing levels of cadmium.
  • A Lithuanian study that compared cadmium levels of breast cancer patients and women with benign breast tumors reported higher concentrations of cadmium in the breast tumors and urine of breast cancer patients. Breast cancer patients with ER+ disease had significantly higher levels of cadmium in their breast tissue than patients with ER- tumors.
  • A U.S. study that matched breast cancer patients and cancer-free controls reported that women in the highest fourth of urinary cadmium levels had twice the breast cancer risk of those in the lowest quartile. The study also reported a statistically significant increase in breast cancer risk with increasing cadmium level.
  • Several human and animal studies have reported that cadmium exposure is associated with increased breast density, a strong marker of breast cancer risk.

Non-food sources of exposure to cadmium

Cadmium is easily absorbed through the lungs, less easily absorbed in the digestive tract, and difficult to absorb through the skin. Cadmium is released into the environment from (1) making and using phosphate fertilizers; (2) automobile exhaust; (3) mining and metal smelting operations; (4) burning coal, oil or garbage; (5) iron and steel production; and (6) disposal of metal products. While U.S. Environmental Protection Agency regulations have been successful in reducing the cadmium exposure of the general population to levels considered safe, people living near or working in industries that conduct any of the above activities might be exposed to relatively high levels of cadmium in the air. Since cadmium is found in car exhaust, soils near roads can have elevated levels.

Crafts, toys and jewelry

Artisans or small business owners who make jewelry or stained glass, or work with paints containing cadmium, should take steps to minimize their exposure to it. Silver solder contains cadmium and ought to be handled carefully. Long-term exposure to cadmium plating baths should be avoided. Artists who work with cadmium pigments (commonly used in strong oranges, reds, and yellows) should also take precautions.
Because it is used in pigments, cadmium is sometimes found in plastic toys and food containers, especially those manufactured in Asia. For example, high levels of cadmium have been found in lines of jewelry meant for children and sold at large retailers.

Smoking

Cigarettes are also a significant source of cadmium exposure. The tobacco plant is particularly efficient at taking up and storing cadmium from the soil. Smokers have approximately double the cadmium in their bodies as nonsmokers. However, breathing secondhand smoke is not believed to be a significant source of cadmium exposure.

Food sources of cadmium

Although cadmium is more easily absorbed through the lungs, most U.S. nonsmokers get their exposure from food. Cadmium particles settling from the air can result in high levels of cadmium in surface soils. Once on the ground, cadmium moves through soil layers and is taken up preferentially by certain plants. Cadmium that lands in water tends to sink and accumulate in the sediment at the bottom. Hence, bottom dwellers such as shellfish can have relatively high levels of cadmium.

Cadmium levels vary by country and region

In countries with lax environmental standards, untreated cadmium-containing industrial waste and sewage may be released directly into rivers, lakes and coastal waters and may also contaminate underground sources of water used for irrigation. Countries reported to have significant problems with such pollution include China, India, Pakistan, Thailand, Nigeria and Russia. Phosphate fertilizers and manure used to fertilize crops can also be significant sources of cadmium. In addition, there are large areas of some countries, including the U.S., Canada and China, in which significant levels of cadmium are found naturally in the soil.

Uptake of cadmium in plants and people varies

Certain plants take up and incorporate cadmium more readily than others. These plants include rice and other cereal grains, flaxseed, potatoes, sunflower seeds, peanuts, lettuce, spinach and other leafy vegetables, and tobacco. Generally speaking, cooking is of very limited value as a means of reducing cadmium concentrations in food.
However, some of these plants contain compounds that tend to offset the deleterious effects of cadmium (e.g., the iron in spinach). Also, other dietary components can influence the impact of cadmium intake on health. For example, curcumin, piperine (found in black pepper), selenium, zinc and iron all appear to protect against cadmium toxicity. Smokers with high fruit consumption have lower blood cadmium concentrations of than those with low fruit consumption. Women with iron deficiency have increased uptake of ingested cadmium. In other words, nutritional status can be an important determinant of cadmium absorption.

Specific foods of concern

Most U.S. women can limit their cadmium exposure by restricting their intake of the small group of foods below. Sometime we fall into the habit of regularly consuming a particular food that appears to be healthy, or at least not harmful. If one of the foods below falls into this category for you, make the necessary adjustments to reduce or eliminate this source of cadmium:
  • Shellfish: Various types of shellfish from locations around the world have been found to incorporate cadmium as a result of industrial pollution. Most low-priced shrimp sold in the U.S. are sourced from parts of Asia known to have heavy metal pollution in coastal waters. The problem is more acute in shellfish from countries with limited pollution control and regulation. However, the problem is not limited to such countries. For example, oysters from the both the West and East coasts of Canada have been reported to contain high levels of cadmium. Continuous monitoring of water conditions and shellfish health is rare, even in the U.S.
  • Flaxseed: Flaxseed can absorb unacceptable levels of cadmium. Areas of Canada, which is the world's largest producer of flaxseed, have high levels of cadmium in the soil. North and South Dakota, the two largest producing U.S. states, also are known to have cadmium-rich soils. The other major flaxseed producers are China and India, both known for heavy metal pollution in some regions. It is possible that flaxseed from high-cadmium areas are reaching the U.S. consumer. The organic label does not necessarily mean a low-cadmium product. We recommend that consumers use flaxseed that is stated to have low levels of cadmium. Note that refined flaxseed oil has negligible levels of cadmium and other heavy metals.
  • Sunflower seeds: Sunflower plants have a tendency to accumulate cadmium — sunflower seeds and kernels are a dietary source of cadmium. Sunflower seeds are grown either for sunflower oil production or for consumption as seeds (confectionary sunflower seeds). U.S. confectionary sunflower seeds are grown primarily in North and South Dakota, a region with relatively high soil cadmium levels. Stricter European rules on cadmium in confectionary sunflower seeds have caused U.S. sunflower seeds with relatively low levels of cadmium to be diverted to the European market. Efforts have been under way for several years to breed sunflower hybrids that will take up less cadmium, however it is not clear to what extent U.S. consumers are benefiting from such steps.
  • Rice: Rice represents a path of cadmium exposure when the rice is grown in contaminated irrigation water or soil. Southern Louisiana is home to numerous oil refineries and petrochemical plants that have introduced cadmium to some of the soil used for rice production, in addition to cadmium contributed in previous decades by phosphate fertilizers. Although the U.S. is a net rice exporter, it imports specialty rice varieties such as jasmine and Basmati rice from countries such as Thailand and India. This rice is often grown under conditions that would be unacceptable inside U.S. borders. Rice grown in California is most likely to have low levels of heavy metal contaminants.
  • Dried apricots: Significant levels of cadmium have been detected in dried apricots from Turkey. Most U.S. apricots are grown in California and Washington state. However, the U.S. imports significant quantities of dried apricots from Turkey.
  • Chocolate: Chocolate, especially dark chocolate, can also incorporate significant levels of cadmium. The European Commission has established maximum cadmium levels in all foods that include cacao, suggesting that higher cadmium chocolate products are more likely to reach the U.S. It is next to impossible to determine the cadmium content of chocolate sold in the U.S.
  • Escargot: Free range escargot (snails) have been found to accumulate cadmium in their tissues from soils containing cadmium. Commercially farm-raised snails typically are fed a diet of ground cereals. Free range snails (which are considered superior in taste and texture) consume a variety of decayed matter, dead animals and insects, and a wide variety of leaves. In the process, they ingest soil. Snails can also become contaminated by roadside car exhaust fumes.
  • Indian mustard: Indian mustard (black mustard) is known for its tendency to incorporate heavy metals, including cadmium, from soil. As noted above, heavy metal contamination of agricultural soils and stream sediments have been reported in many countries, including in China near coal and copper mines, in India near tanneries, and in Russia near uranium plants and heavy metal smelting complexes. Much of the imported Indian mustard consumed in the U.S. is imported from Canada, but it also comes from parts of the old Soviet Union, India and China. Buyers of Indian mustard from specialty markets should be aware of its source and assure themselves of its safety and quality.
Finally, consumers growing their own vegetables should avoid using roadside plots.

Sources of information provided in this webpage

The food lists and other information above, which are updated continually as new research becomes available, have been developed based solely on the results of academic studies. Clicking on any of the foods will take you to its webpage, which contains specific information concerning that food's relationship to breast cancer (including its overall ranking), as well as links to supporting studies.
Below are links to 20 recent studies concerning this topic. For a more complete list of studies, please click on cadmium.