Some dark chocolates contain heavy metals. Should you be concerned?

The study’s findings are not a reason to stop eating dark chocolate, Frame said. Some studies suggest flavonoids found in dark chocolate may lower the risk of heart disease and high blood pressure.

But these small exposures to heavy metals, plus other exposures in an individual’s diet, could amount to higher blood lead levels over time. “And that is something that we all need to be aware of,” Frame said.

“I would not want someone to be afraid of chocolate. That would be the worst thing that could come out of the study to me,” she said. “Frankly, it’s a small contributor to our diet.”

The facts

• ConsumerLabs selected cocoa products to test largely using a ranked survey completed by thousands of respondents on the company’s website every year, the researchers write in the study.
• ConsumerLabs purchased the products and paid for them to be tested at two independent labs, Frame said. Researchers at George Washington University analyzed the results, without knowing the names and brands of the products that were tested.
• Forty-three percent of the 72 cocoa-containing products had amounts of lead that exceed California’s maximum allowable dose level for the heavy metal, which is 0.5 micrograms per day. Thirty-five percent of the products had amounts of cadmium that exceed California’s rules.
• Seventy of the 72 products tested contained amounts of lead lower than the Food and Drug Administration’s benchmark of 2.2 micrograms per day for children. The benchmark is set nearly 10 times lower than the amount of lead from food required to meet the marker the Centers for Disease Control and Prevention uses to identify high blood lead levels.
• Some samples had “much higher” levels of lead and other heavy metals detected; there was “a bit of variability” in dark chocolate and other cocoa products, Frame said. One sample tested had 3.13 micrograms of lead per serving, the highest detected in the study.
• The researchers say the heavy metals detected “may not pose any appreciable risk for the average person when consumed as a single-serving.”
• Jacob Hands, the co-lead author of the study and a medical student at George Washington University School of Medicine and Health Sciences, said the researchers chose California’s regulation for the analysis because it is a conservative estimate. Frame also said the state’s regulation is what is generally used in other studies.

The study was published in the journal Frontiers in Nutrition on Wednesday.

Hands is a contract researcher for Consumer Labs.

Background

The George Washington University study follows the findings of a 2022 investigation by Consumer Reports that detected cadmium and lead in all of the 28 dark chocolate bars tested, as well as follow-up testing of 48 cocoa-containing products in 2023.

In response to questions about the GWU study, an FDA spokesperson said, “while the presence of cadmium and lead in chocolate has been the subject of considerable media attention, experts from around the world have found that chocolate is a minor source of exposure to these contaminants internationally.”

Chocolate, or cocoa, has been historically used as a medicine to treat fatigue and improve digestion. And studies suggest flavonoids found in cocoa can lower the risk of heart disease, high blood pressure and diabetes. But the type of chocolate matters; darker chocolate often contains higher amounts of cocoa and more flavonoids.

Chronic exposure to lead and cadmium is associated with kidney dysfunction and other health problems. Infants, young children and pregnant people can be particularly vulnerable because prolonged lead exposure in early development has been associated with a higher risk of learning disabilities or lower IQ levels.

Young children in the United States are eating and drinking far less lead than they did decades ago — from 43 micrograms per day in 1980, to around 1 microgram per day in 2016 — according to the FDA.

However, lead contamination in food products remains a concern. In the fall, the FDA warned of “extremely high” levels of lead detected in three brand names of cinnamon applesauce puree pouches. And the agency continues to send public health alerts recommending that consumers stop using and dispose of certain ground cinnamon products contaminated with lead.

Frame said the good news is kids generally don’t like eating dark chocolate. The darker the chocolate, the more the cocoa powder and the potential for higher amounts of lead, cadmium or other metals.

“I don’t think we need to worry as much about kids,” Frame said.

And cocoa powders — such as mixes used for hot chocolate — are often more akin to milk chocolate with less raw cocoa than dark chocolate, she said.

What the industry says

Christopher Gindlesperger, the senior vice president of public affairs and communications for the National Confectioners Association, the trade organization for the candy industry in the United States, said chocolate and cocoa are safe to eat, and food safety and product quality “remain our highest priorities.”

“Consumers understand that chocolate and candy are occasional treats and not center-of-the-plate foods,” Gindlesperger wrote in an email.

Why are heavy metals in dark chocolate?

Cadmium in the soil can transfer into a cacoa tree growing there, leading to a “natural contamination,” said Tewodros Godebo, an assistant professor of environmental health sciences at Tulane University School of Public Health and Tropical Medicine.

Lead, though, appears to be introduced during the production of cocoa products, not from the soil, but potentially during drying, processing or packaging, Godebo said.

What other experts are saying

Katarzyna Kordas, an associate professor of epidemiology and environmental health at University of Buffalo, said in an email that the study’s findings demonstrate “not all chocolate or cocoa products are created equal.” Some contain more metal than others.

The amount of a metal someone is exposed to is a function of how much of the contaminant is in the food, how much the person consumes and whether they’re eating on an empty or full stomach, Kordas said. “We tend to absorb proportionally more metals on an empty stomach,” she said.

But the amount of lead or cadmium detected in the study is often below stringent reference values and that suggests “the level of concern may be low,” Kordas said.

Godebo said California’s regulations on heavy metals are “very conservative,” making it difficult to translate what the amounts of cadmium or lead mean for the general population. People are exposed to metals every day, and other types of foods, vegetables and fruits can be more significant sources of heavy metals, he said.

“Of course, we want a negligible amount of exposure,” Godebo said. “But, literally, it’s impossible.”

In a study published in June, Godebo and other researchers at Tulane University tested 155 dark and milk chocolates for lead and other heavy metals and concluded eating one ounce of dark chocolate a day “poses no health concerns for adults.” The researchers also determined four of the chocolate bars tested had cadmium levels that could pose a risk to young children.

“What we’ve found is that it’s quite safe to consume dark and milk chocolates,” Godebo said in a statement in June about the study.

Should I eat dark chocolate?

Frame said she continues to eat chocolate.

People can eat a diverse diet of different foods to reduce any potential exposure to lead, or other heavy metals, from a part of their diet, Frame said.

Anyone concerned about their exposure to lead, cadmium or other metals should ask their physician for a blood test, Frame said. “Then you’ll have a ground truth,” to determine whether relatively small exposures in your diet could be adding up to higher blood lead levels.

“I think it’s pretty clear, actually, that having one ounce of chocolate a day is not detrimental,” Frame said. But people can be cognizant of how much they’re having and how often, she said.

Frame said she eats chocolate every other day.

“It makes it feel more like a treat,” she said.