What Is Cadmium? Health Effects, Risk Factors for Exposure, and More

If you’re worried that heavy metals like cadmium might be lurking in your food, you’re not alone — and you may not be wrong, either. But that doesn’t mean there’s cause for alarm.

An investigation published in December 2022 in Consumer Reports, for example, did lab tests on 28 dark chocolate bars from brands including Hershey’s, Trader Joe’s, Dove, and Ghirardelli and detected the heavy metals cadmium and lead in every single one of them.

And this was just the latest example of cadmium and other heavy metals in foods. Numerous studies have found cadmium in coffee, fruits, and green, leafy veggies. And an investigation published in 2021 in Consumer Reports found it in many commonly used dried spices.

“Cadmium is a natural element, and we are exposed to it all the time,” says Jaymie Meliker, PhD, a public health professor at the Renaissance School of Medicine at Stony Brook University in New York. “The question is fundamentally about dose: How much are we exposed to and at what levels are we at risk?”

Turns out, measuring cadmium exposure and the health risks involved is complex, but the good news is not everyone needs to be worried.

Read on to get the rundown on how you might get exposed to cadmium, what level of exposure could be dangerous, and what you can do to keep yourself and your family healthy.

What Is Cadmium?

Cadmium is listed in the seventh position of the harmful substances priority list to reduce exposure to humans, behind others like arsenic, lead, and mercury, according to the Centers for Disease Control and Prevention's (CDC) Agency for Toxic Substances and Disease Registry.

Cadmium is a relatively rare metal found naturally in the earth’s crust, according to the Dartmouth Toxic Metals Superfund Research Program. While natural processes like erosion can release cadmium into the environment slowly over time, human activities like mining, manufacturing, and farming are the main ways cadmium is released into the environment.

Discovered in Germany in the early 1800s, cadmium was first used to make pigments and paints because it can produce vibrant yellow, orange, and red colors, according to the Occupational Safety and Health Administration (OSHA).

More recently, cadmium has been used as an erosion-protection coating on iron and steel; a main component in nickel-cadmium rechargeable batteries; and for manufacturing solar cells, plastics, and pigments, according to OSHA.

Activities like mining, smelting, and refining metal ores like zinc, lead, and copper release cadmium into the environment, according to Dartmouth. Burning fossil fuels, incinerating waste, and producing steel also release cadmium. The United States is the biggest producer of cadmium, generating an estimated 1,100 tons of the heavy metal each year.

Cadmium gets into food when plants absorb it from the soil, air, and water where they are grown, says Luz Claudio, PhD, a professor of environmental medicine and public health at the Icahn Mount Sinai School of Medicine in New York City.

“The reason that there is so much cadmium in foods is because of the industrialization of agriculture with its heavy use of fertilizers that can contain high levels of cadmium,” Dr. Claudio says. “Cadmium can also come from manufacturing activities that release this metal into the environment.”

It’s unclear.

One reason is regulations vary even within the United States, experts point out. These amounts are gauged by a metric called maximum allowable dose level, or MADL, which indicates the maximum allowable dose that is thought to be safe, Dr. Meliker says.

“Of course, nothing is 100 percent safe, and we determine safety by a very crude method that essentially takes a dose that is observed to cause harm,” Meliker says. Also, this dose is often based on animal research, and then scientists use those values to try to calculate how much would be unsafe for humans or for certain vulnerable subpopulations such as infants or children.

Part of the challenge in determining the exact amount of cadmium that may be unsafe to eat or breathe is that studies are not going to expose people to cadmium specifically to test how much is dangerous, Meliker adds.

So while the answer isn’t straightforward, limiting exposure as much as possible, particularly by not smoking, still makes sense, Meliker says.

Consuming food with cadmium and smoking cigarettes are the primary sources of cadmium exposure, says Tunde Akinleye, test program leader of food safety at Consumer Reports in Yonkers, New York.

“In the United States, for nonsmokers, the primary source of cadmium exposure is the food supply,” Akinleye says. “In general, leafy vegetables such as lettuce and spinach, potatoes and grains, peanuts, soybeans, and sunflower seeds can contain high levels of cadmium.”

Candy probably isn’t the biggest offender despite lab tests of dark chocolate run by Consumer Reports finding that 1 ounce of most samples contained more than 0.5 micrograms (mcg) of cadmium. This exceeds the maximum allowable dose levels (MADL) under California regulations, which are the strictest in the United States. However, what's unclear for dark chocolate and other food sources of cadmium is its so-called bioavailability, or the percentage of ingested cadmium that is absorbed through the digestive tract and has the potential to be toxic, says Meliker.

Overall, the amount of cadmium in food depends on the amount of cadmium it’s exposed to when grown (factors like location and fertilizer use can affect exposure levels) and the amount of cadmium absorbed also varies by food, experts say. That said, for most foods, scientists estimate that about 1 to 10 percent of cadmium gets absorbed, Meliker says. If that’s the case, a daily ounce of dark chocolate is probably innocuous.

Organ meats — like the liver or kidney from animals — are far and away the largest potential source of dietary cadmium, says Meliker. A main dish made from some kidney meats might have more than 50 mcg of cadmium. “But most people don’t eat organ meats very frequently,” Meliker notes.

Shellfish are another big source of cadmium, and might contain 5 to 10 mcg per meal, Meliker notes. “But we believe the bioavailability from shellfish is low,” Meliker notes, making this another source that may not result in a lot of cadmium accumulation in the human body.

Among nonsmokers, there are several foods that can account for the bulk of cadmium exposure, according to the European Commission (EC). The EC lists the following foods as main offenders when it comes to cadmium exposure:

• Cereals
• Leafy vegetables
• Nuts and legumes
• Potatoes and root vegetables
• Meat

For smokers, cigarettes are a far bigger concern when it comes to cadmium exposure, Meliker says. With each cigarette, people can inhale 1 to 2 mcg of cadmium, amounting to up to 40 mcg daily for a pack-a-day smoker, Meliker estimates. While there are no specific cadmium exposure guidelines for cigarette smoke, OSHA suggests that workplaces limit average cadmium exposure over an eight-hour shift to less than 2.5 mcg.

Not all heavy metals are bad for you. Iron, for example, is a main component in hemoglobin, a protein in red blood cells that transports oxygen from the lungs to the rest of the body, according to the Harvard T.H. Chan School of Public Health.

But there are no health benefits to cadmium, and it can become increasingly harmful as more and more of it accumulates in the body, says Claudio.

Most often, people may be exposed to low levels of cadmium over long periods of time through smoking or eating certain foods. This can cause cadmium to slowly build up in the kidneys, causing kidney disease, and also contribute to fragile bones and certain cancers, according to the CDC.

If you were exposed to toxically high levels of cadmium at work or a contaminated food source, it is possible to develop upset stomach, vomiting, diarrhea, or respiratory symptoms, according to the CDC. This can also happen when people consume foods or drinks stored in containers with a cadmium paint or glaze, according to the Agency for Toxic Substances and Disease Registry (ATSDR).

Acute cadmium poisoning is also a risk for people who have exposure to this metal on the job, according to ATSDR. High-risk jobs include cadmium alloy production, welding that involves cadmium-coated steel, and cadmium smelting and refining.

For these workers, cadmium inhalation can cause severe and sometimes fatal lung diseases, ATSDR notes. They can start having acute symptoms 4 to 10 hours after exposure to cadmium at work.

Initial symptoms can include chills, fever and muscle aches, according to ATSDR. Symptoms can progress to include chest pain, cough, and shortness of breath. They can also develop two serious and potentially life-threatening conditions that impair breathing: chemical pneumonitis — a severe form of inflammation in the lungs that makes it difficult to breathe — or pulmonary edema, a dangerous accumulation of fluid in the lungs. Yet these more severe reactions are not connected to common low-level exposure from eating the aforementioned foods.

For most people who aren’t exposed to cadmium at work, the main sources of cadmium exposure are foods and smoking, according to ATSDR.

Vegetarians can have a higher risk for cadmium exposure because their diets may contain more foods with higher levels of this heavy metal, such as cereals, nuts, and legumes, according to the European Commission.

In some countries where contaminated soil has led to high levels of cadmium in certain crops, consumption of certain foods can be a big risk factor for a more severe cadmium exposure, according to ATSDR. In Japan, for example, local rice crops often contain high levels of cadmium, and rice consumption is a big risk factor for exposure, according to the ATSDR.

However, smoking is a bigger risk factor for cadmium exposure in the United States, according to the ATSDR. Among Americans, one study published in Environmental Science and Pollution Research International identified the following risk factors for exposure to high levels of cadmium:

• Older age
• Poverty
• Lower education levels
• Smoking
• Female sex

In the United States, cadmium exposure has declined over the past few decades among both men and women, according to the study in Environmental Science and Pollution Research International that examined data on cadmium levels in blood samples from about 48,000 adults and urine samples from roughly 33,000 adults.

However, this study also found that about 8 percent of men and 19 percent of women have had enough cadmium exposure reported to show harmful effects on the kidney.

A report from the CDC suggests that the risk of cadmium exposure is higher among smokers and people exposed on the job.

While the exact prevalence of poisoning from cadmium and other heavy metals is unknown, it’s rare, and becoming less common as these substances are removed from more consumer products, according to Cleveland Clinic.

For people who have exposure to cadmium at work, safety practices like using alternative materials when possible, creating proper ventilation, and wearing protective equipment to minimize contact and inhalation can all help reduce the exposure risk, according to OSHA.

There’s a lot the rest of us with desk jobs can do, too, says Toby Amidor, RD, author of The Family Immunity Cookbook. The main things she advises are:

• Don’t smoke
• Eat a balanced diet with a variety of foods from different food groups
• If you drink well water, test it for cadmium
• If you grow your own veggies, test your soil for cadmium

One thing you don’t need to do is give up dark chocolate, Amidor says. “You will not get cadmium poisoning from one bite or even one bar of chocolate,” Amidor adds. “You would need to eat a lot of higher-cadmium foods over a much longer period of time to get any toxicity effects.”

You may not be able to control whether you’re exposed to foods that absorb cadmium from the soil, or avoid some exposure to cadmium if you live with a smoker. But you can do a lot to limit your risk, says Meliker.

“The No. 1 thing people should do is not smoke cigarettes,” Meliker says. Second, don’t rethink including healthy foods in your diet — even if some of those foods contain cadmium, as these pose a relatively low risk to human health. If you’re concerned about exposure to cadmium, consult your primary care doctor.