Chocolate often makes headlines for its potential cardiovascular benefits, largely attributed to its flavonoids (flavanols in particular), which have antioxidant, anti-inflammatory, and anti-clotting properties. Among the more recent studies was one in the American Journal of Clinical Nutrition, which found that a flavanol-enriched cocoa powder improved some measures of cognitive functioning in older people, as well as blood pressure, cholesterol, and blood sugar.
But if you’re a chocoholic—or just a regular consumer—you may have been startled by reports from the independent testing company ConsumerLab.com, which found that cocoa (the key ingredient in chocolate) also harbors something far less welcome: cadmium. Actually, this was not really news, since it has long been known that cocoa (and many other foods) often contain trace amounts of heavy metals.
Cadmium is naturally found in soil—a result, for example, of volcanic activity, forest fires, and weathering of rocks—and is taken up by many plants, including cocoa plants. Soil can also be contaminated by “man-made” sources of cadmium, such as from the manufacturing of certain batteries and the use of phosphate fertilizers. How much of the heavy metal ends up in cocoa beans depends on the geographic region, soil acidity, plant variety, and other factors. Further contamination may occur, to varying degrees, during processing and manufacturing of cocoa products as well as during transport and storage.
Cadmium accumulates in the body and can have detrimental effects on the kidneys, lungs, bones, and possibly fetal development; it’s also classified as a probable human carcinogen. Unlike the Canadian government and the European Union, the FDA has not set cadmium limits in foods or supplements. The World Health Organization (WHO) suggests a maximum of 0.3 micrograms per gram in dried plants. And California requires a warning label on products that have more than 4.1 micrograms of cadmium per daily serving of a single product. Cadmium limits have been determined in many different ways, but it’s unclear which approach is best.
Good news, bad news
For its report, last updated in June 2015, ConsumerLab.com analyzed 21 cocoa products, mostly cocoa powders and dark chocolate bars, but also several cocoa supplements. First, the good news: All seven dark chocolate bars fell below the WHO limits for cadmium (as well as below a limit for arsenic), though one exceeded California’s daily cadmium limit. All the supplements also passed testing.
The bad news was that of eight cocoa powders, six failed because of excessive cadmium levels, with most having three to five times the WHO limit. Two had more than three times the California limit and one had five times the limit. And one cocoa powder that fell below the cadmium limit contained a small amount of lead, as did two other powders. Lead is another toxic metal that is regularly detected in cocoa products.
According to ConsumerLab.com, dark chocolate seems to be a “cleaner” source of flavanols than cocoa powders. As Tod Cooperman, the company’s president, explained, flavanols are about four times more concentrated in dark chocolate than in cocoa powder—so to get an equal amount of flavanols, you’d consume about four times more cadmium from cocoa powder than from dark chocolate. On the other hand, when comparing chocolate bars and cocoa powders by serving sizes (about 40 grams and 5 grams, respectively), the bars had nearly as much cadmium, on average, as the powders.
“A disturbing surprise”
That’s what ConsumerLab.com called its findings, though it’s not clear how much cocoa or chocolate you’d have to consume—and for how long—to develop health problems. Cadmium is not well absorbed by the body when ingested, and consuming adequate calcium, iron, and zinc may help reduce cadmium absorption further. But because the heavy metal accumulates in the body, it can do damage over time. Thus, minimizing exposure to cadmium and other heavy metals is prudent, and researchers are looking for ways to reduce levels in cocoa. At an international workshop, several recommendations were proposed for cocoa farmers, such as making soil less acidic, not using phosphate fertilizers, and selecting cocoa varieties that accumulate little cadmium.
The bigger picture
Cocoa is just one of many sources of cadmium. Lots of foods contain trace amounts, notably rice, as well as seaweed, seafood, and some organ meats; even peanuts, sunflower seeds, leafy greens, potatoes, bread, and mushrooms contribute to dietary cadmium intake. In fact, most foods—even ones we consider to be very healthful—carry some kind of potential risk. Smoking is another route by which cadmium enters the body, and absorption is more efficient through the lungs than the gastrointestinal tract. Some people are also exposed to cadmium-contaminated air—sometimes at quite high levels—depending on where they work or live.
Words to the wise
There’s no reason to avoid cocoa or chocolate, though children in particular should not go overboard on cocoa powder, whether in hot cocoa or baked goods. “Dutch” (alkali) processing of cocoa powders—which most undergo—destroys much of the flavanols, anyway. Dark chocolate (as opposed to milk chocolate) can be a good source of flavanols (the higher the percent cocoa, the better), but because trace amounts of cadmium and lead can still be lurking in your bars, keep moderation in mind. Just a small square a day may be enough to satisfy, while minimizing the risk of heavy metals.
What about cocoa supplements? They all passed muster in ConsumerLab.com’s analysis, but we don’t recommend them. Other testing by the company found that they varied widely in flavanol content and often didn’t have the amounts claimed on the labels—plus, the supplements have not been proven to have health benefits. The best way to get an array of antioxidant phytochemicals on a daily basis—including ones similar to those in cocoa and chocolate—is by eating a variety of fruits and vegetables. They have fewer calories than chocolate and an abundance of vitamins and minerals, along with fiber and other healthful plant compounds.