Q: There were a number of news articles about cadmium and lead in dark chocolate recently, and it made me incredibly anxious as someone who eats very dark chocolate every day — including during my pregnancy and breastfeeding! What would experts say about how much I should worry?
The bad news came in mid-December: Consumer Reports published an investigation showing that 23 of the 28 dark chocolate bars it had tested from various brands contained concerning levels of lead, cadmium or both. Research has previously shown that consuming dark chocolate may have several health benefits, including lowered blood pressure, better cholesterol and a reduced risk of heart disease. So the news that it could also contain toxic heavy metals has worried many consumers.
Melissa Melough, an assistant professor of behavioral health and nutrition at the University of Delaware, said she was curious to see the actual data as soon as she read the headlines: “These types of reports always get sensationalized.” When she took a closer look, though, she agreed that the results were worrisome.
“If you’re a regular consumer of these dark chocolates, I would be concerned,” she said, especially if you’re pregnant or breastfeeding or have a child who enjoys dark chocolate, as the health effects of these metals are most concerning during early brain development.
How much lead and cadmium are we talking about?
The Consumer Reports investigation was not peer-reviewed, but the levels of cadmium and lead found in the dark chocolate were similar to those reported in a more comprehensive study of cocoa and chocolate products published by researchers at the Food and Drug Administration in 2018. The F.D.A. study found that dark chocolate had, on average, 7.6 micrograms of cadmium and 0.8 micrograms of lead per one-ounce serving, and some products had three or four times as much. (Milk chocolate, which contains less cocoa, had much lower concentrations.)
Compared with more than 300 other foods tested by the F.D.A. in a separate study, dark chocolate had the third-highest concentrations of both cadmium and lead, exceeded only by baking powder and cocoa powder for lead, and cocoa powder and sunflower seeds for cadmium.
Researchers and chocolate companies have been aware of the high levels of lead and cadmium in cocoa products for decades, said Jerome Nriagu, a professor emeritus of environmental health sciences at the University of Michigan School of Public Health. In a 2005 study, he and his colleagues also found that the lead concentrations in cocoa powder and chocolate products were among the highest of any foods. As You Sow, a social responsibility nonprofit, has since put pressure on chocolate companies to address the issue, outlining strategies that can reduce the amount of cadmium and lead in chocolate.
How do these metals end up in chocolate in the first place, and are the levels high enough to be harmful?
Lead and cadmium are both natural elements in the Earth’s crust, but human activities like mining, manufacturing, transportation and agriculture have increased their levels in the air, soil and water. Because of their presence in the environment, these metals are ubiquitous in the food supply, said Kantha Shelke, a senior lecturer on food safety at Johns Hopkins University and a consultant to food manufacturers, including cocoa processors. “Total avoidance of lead and cadmium is impossible,” she said in an email.
But it’s clear that cadmium and lead can cause harm to the body, especially during pregnancy and childhood. Long-term exposure to cadmium can lead to bone fragility as well as kidney and lung damage. Lead can affect nearly every organ system in the body, especially the nervous system.
Since potential toxins can’t be tested directly on humans, it’s difficult to estimate how much of a substance is enough to be harmful. What’s more, different agencies have different food safety standards. European safety standards, for example, state that a 130-pound person should consume no more than 21 micrograms of cadmium per day to avoid health risks; therefore, an ounce of dark chocolate that contains seven or eight micrograms is unlikely to be harmful, Dr. Shelke said. (People who weigh more or less would have different limits.)
On the other hand, the “minimal risk level” for daily cadmium intake set by the U.S. Agency for Toxic Substances and Disease Registry is about six micrograms for a 130-pound person. A single one-ounce serving of dark chocolate could exceed that amount, and people in the United States consume an average of five micrograms of cadmium per day via other food sources, according to a 2019 study by Dr. Melough and her colleagues.
There is no established safe intake level for lead in the United States, because even the lowest blood lead levels are associated with adverse neurodevelopmental effects in children. However, the F.D.A. does have a recommended maximum for lead in candy, above which the agency may take action to limit a product’s sales. The amount of lead typically found in dark chocolate is lower than this maximum.
Despite the variability in safety standards, it’s clear that dark chocolate is relatively high in both metals and can significantly increase a person’s overall daily intake.
What’s a chocolate lover to do?
The upside is that you don’t have to give up dark chocolate entirely. Just enjoy it in moderation, and as part of a varied diet, Dr. Melough said.
If you eat chocolate often, it may be worth choosing products with lower heavy metal concentrations, she said. As You Sow’s website keeps track of cadmium and lead levels in products from several chocolate brands.
A general rule of thumb is to consume no more than an ounce per day, Dr. Melough said. Eating more than that raises concerns not only about heavy metals, but also about high levels of saturated fat, she added. And research has shown that you can reap the health benefits of dark chocolate by eating as little as one-third of an ounce per day.
Because of the greater risk of harm from heavy metals during early stages of human development, she said, those who are pregnant or breastfeeding should consider eating dark chocolate only once or twice a week. The same goes for children.
But in the longer term, Dr. Melough said, consumers shouldn’t have to carry the burden of worrying about heavy metals in their chocolate. “I do think this has to fall on industry and producers to change their methods” to reduce cadmium and lead in their products, she said.
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