NBC News
A new study reveals that dark chocolate products sold across the country may contain excessive amounts of heavy metals.
The research, led by scientists at George Washington University and published Wednesday in the journal Frontiers in Nutrition, examined more than 70 dark chocolate products from retailers including Whole Foods Market, Amazon and GNC. They were tested for heavy metals such as lead, cadmium and arsenic.
Overall, 43 percent of the products studied exceeded acceptable levels for lead and 35 percent exceeded acceptable levels for cadmium, according to the study, which was based on a California law that sets maximum allowable dose levels of heavy metals in foods. Food researchers typically use the 1986 regulation, known as Prop 65, as a safety standard because the Food and Drug Administration does not set limits for heavy metals in most foods, said Leigh Frame, director of integrative medicine at the George Washington University School of Medicine and Health Sciences and senior author on the study.
The FDA has indeed suggested limits on chocolate and sugar-based candy, but only for children.
Under California guidelines, the threshold for heavy metals in food is 0.5 micrograms per day. For the study, the scientists calculated the number of micrograms per day that people would be exposed to if they ate the amounts suggested on chocolate product labels. They found that the chocolate samples ranged from 0 to 3,316 mcg per daily serving. Levels of cadmium, a carcinogen at elevated levels, ranged from 0.29 to 14.12 mcg, with the limit being 4.1 mcg per day.
None of the products exceeded the maximum level of arsenic.
Frame noted that since the products contained varying amounts of lead, limiting consumption is the only sure way to reduce exposure.
“Don’t have large amounts of chocolate every day,” she said. “A one-ounce serving is what we recommend, or maybe two ounces every other day.”
How to avoid lead in food
Researchers agree that completely avoiding heavy metals in our diet is almost impossible. Foods such as rice, fish, fruits and vegetables are known to contain varying amounts of metals. Although the body can eliminate heavy metals naturally through sweat and urine, if consumed in high quantities they can accumulate in the body and damage major organs.
“You can’t really avoid exposure to heavy metals in your diet,” Frame said. “It’s not really about avoiding them, it’s about making sure you’re not getting too much of them.”
He emphasized dietary diversity to avoid excessive exposure to any one substance.
“Not eating the same thing every day helps protect you from many things, including heavy metals,” she said.
The authors intentionally omitted which brands had which concentrations of metals, given that levels could vary even within the same company. Interestingly, the study found that organic cocoa products were more likely to have higher levels of cadmium and lead.
“Organic foods don’t necessarily mean they’ve been tested for exposure to toxic metals like lead, cadmium and arsenic,” said Manish Arora, vice chair of the department of environmental medicine and climate science at the Icahn School of Medicine at Mount Sinai in New York.
“I think for most people ‘organic’ just means cleaner, and in this case it’s counterintuitive,” he said.
Arora, who was not involved in the study, said that while the new research was solid, a big question mark is how the heavy metals got into the chocolate products.
“Is it due to processing, cultivation, soil type, fertilizers or any other agricultural process?” he asked. “We are left without knowing for certain where the metal actually entered the food chain.”
Previous research has found that lead and cadmium can enter dark chocolate through different routes. Cadmium arrives primarily through the cocoa plant, which absorbs it from the soil, while lead can be introduced at various points in the manufacturing process, such as harvesting, drying and fermenting the cocoa bean.
There is no safe level of lead. Although the FDA does not set limits for cadmium or arsenic, nearly all of the chocolate bars in the study were below its recommended level of lead: 2.2 mcg per day for children under 7 years old and 8.8 mcg per day for women of childbearing age.
This contrasts with California guidelines, which under Proposition 65 tend to be more conservative, Frame said.
Tewodros Godebo, an associate professor of environmental health sciences at Tulane University’s School of Public Health and Tropical Medicine, said he believes Prop 65’s guidelines are too conservative and may cause unnecessary panic. This year, he published his own study, in which his team analyzed more than 100 chocolate products.
Instead of Prop 65 limits, Godebo’s research used a method proposed by the Environmental Protection Agency that found that the levels of heavy metals in chocolate were not high enough to be of concern to adults. The EPA routinely uses the formula, called a hazard quotient, to determine a substance’s toxicity.
However, she recommended not consuming more than one ounce of dark chocolate a day and limiting consumption by children and pregnant women.
The new study did not examine milk chocolate, but theoretically it should have a lower risk of heavy metal contamination, Frame added. That’s because the metals are thought to come from the cocoa powder itself, which is present in higher levels in dark chocolate.
