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Dark chocolate has some health benefits but too much might expose you to other risks.YelenaYemchuk/iStockPhoto / Getty Images

Q: I’ve been hearing that dark chocolate can be high in heavy metals. Is this a real concern? How much is safe to eat?

If your daily diet includes a square (or two) of dark chocolate, you’re not alone. Many people savour this treat for its rich flavour along with its hefty dose of flavonols, antioxidants linked to heart health.

Now for some less welcome news.

According to scientists from Consumer Reports, a U.S. based independent non-profit organization, your favourite bar of dark chocolate may contain worrisome levels of cadmium and lead, harmful heavy metals.

Here’s what to know – and why it’s not necessary to give up dark chocolate completely.

About cadmium, lead

Cadmium and lead, as well as other heavy metals (arsenic and mercury), are naturally occurring elements in rock and soil. Heavy metals are also released into the environment through industrial processes such as mining, manufacturing and burning fossil fuels, as well as household wastes.

As such, they are ever-present in the food supply. Cadmium is also present in cigarette smoke.

Long-term exposure to lower levels of heavy metals is tied to adverse health effects.

Continuing exposure to cadmium, for example, can cause a buildup of the metal in the kidneys, leading to kidney damage. It’s also linked to lung damage, weakened and painful bones and high blood pressure.

Consistent long-term exposure to lead is associated with harm to the brain, heart and kidneys, as well as reproductive health. Infants and children, as well as those who are pregnant, are especially vulnerable to the danger of long-term lead exposure owing to its harmful effect on brain development.

The new research findings

The Consumer Reports study, released on Dec. 15, analyzed the amount of cadmium and lead in 28 dark chocolate bars, including 21 brands, some of which are available in Canada. Cadmium and lead were detected in all samples.

For 23 of the bars tested eating an ounce (28 g) a day would put adults over the daily maximum allowable dose, according to the California Office of Environmental Health Hazard Assessment, for at least one of these heavy metals. Five of the bars exceeded the thresholds for both cadmium and lead.

A 2018 study conducted by the U.S. Food and Drug Administration found similar levels of cadmium and lead in cocoa and chocolate products available in the U.S.

The Consumer Reports investigation did find that five bars were relatively low in both cadmium and lead.

Keep in mind the Californian maximal allowable dose levels are stricter than the U.S. FDA-recommended maximum for lead in candy and the European Union recommendations for maximum cadmium in dark chocolate. The levels of cadmium and lead found in the dark chocolate bars were within both recommendations.

How do heavy metals get into chocolate?

Dark chocolate, made from cacao beans, contains 50 to 90 per cent cocoa solids, along with cocoa butter and sugar. The higher the percentage of cocoa solids, the higher the flavonol content.

Cocoa solids can also contain heavy metals, especially cadmium. As the cacao plant grows, it takes up and accumulates cadmium from the soil.

Lead can make its way into cocoa solids during harvesting of the beans and/or manufacturing of chocolate.

What to do?

According to assessments conducted by Health Canada, chocolate contributes marginally to our dietary intake of cadmium and lead. As such, the government has not established maximum levels for these heavy metals in chocolate products.

Even so, there ways to enjoy dark chocolate while, at the same time, minimizing potential risks.

Moderation is key. Stick to a one ounce serving of dark chocolate and don’t eat it every day. The health risk comes with continuing and frequent consumption.

To be cautious, young children and those who are pregnant or breastfeeding should limit their dark chocolate intake to once or twice a week.

If you eat dark chocolate often, consider choosing a bar with a lower percentage of cocoa solids; cadmium levels tend to increase with the percentage of cacao solids as well. Or alternate with milk chocolate, which contains 10 to 50 per cent cocoa solids.

If it’s protective flavonols you’re looking for, you’ll also find these anti-inflammatory and antioxidant plant compounds in berries, red grapes, pomegranate seeds, apples, pears and tea (black, green and white).

Leslie Beck, a Toronto-based private practice dietitian, is director of food and nutrition at Medcan. Follow her on Twitter @LeslieBeckRD

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