Is it dangerous to eat dark chocolate because of its cadmium and lead content?

A long time ago, many people switched from consuming milk chocolate to dark chocolate (much higher in cocoa), in search of healthier food. Today, however, some news suggests that chocolate may be contaminated with cadmium and lead…. and that the concentration of these heavy metals may be higher in dark chocolate.

Does this mean that we’re going to have to stop eating it? Well, if we actually analyze the information and put it into context, we can see that the risk isn’t exactly as high as most headlines indicate.

In just a few years, cocoa has gone from being frowned upon — due to its association with unhealthy foods, such as sweetened milk chocolate — to essentially being a superfood. Nowadays, many people include pure cocoa — or chocolate with high cocoa content — in their diet, in search of a beneficial effect on health. But recent news is warning of the supposed danger that its consumption entails, due to its content of heavy metals, specifically cadmium and lead.

This subject has reached the general public. It was first widely-discussed in 2022, although, just a few weeks ago, several studies were published by Consumer Reports. The results revealed that — upon analyzing various products made with cocoa (mostly dark chocolate) — the researchers found high amounts of cadmium and lead content. The reports warn that a large proportion of dark chocolate samples — especially those with cocoa content between 70% and 80% — present amounts of contaminants that are “too high” and “can put health at risk.”

This isn’t a new discovery

This news caught many people by surprise. They didn’t imagine that cocoa could contain heavy metals. Consumers began to wonder where this contamination came from.

But, in reality, this risk is nothing new. It’s actually been known and studied for more than four decades, given the repercussions it can have on health. The first thing that’s done is a risk assessment, which generally consists of four phases.

The first phase consists of identifying the hazards — that is, the potentially dangerous agents that may be associated with cocoa, including cadmium and lead. Both are persistent contaminants that can be found in soil. The first is absorbed by the plant and builds up as it grows, while the second accumulates in the cocoa beans during post-harvest processing (fermentation, drying, hulling, etc.) via dust from the soil or the environment.

The second phase of risk assessment is based on characterizing the hazards, in other words, knowing what effects they can cause. Cadmium is classified as a carcinogen by the International Agency for Research on Cancer (IARC). Its main effect (after prolonged exposure) is kidney dysfunction, although it can also affect the reproductive system and cause other damage, such as bone demineralization.

For its part, lead is classified as a probable carcinogen and can also cause neurotoxic effects, kidney or cardiovascular failure, serious neurological damage to the fetus during pregnancy and even miscarriages. However, this doesn’t mean that eating cocoa or chocolate will necessarily cause these problems. Risk depends on aspects such as the amount of cadmium and lead in the cocoa, the amount of cocoa we eat, or our body weight. That’s why the third phase of risk assessment consists of evaluating exposure to these contaminants.

Finally, it’s necessary to characterize the risk: that is, determine the probability that these hazards can cause health damage. From all this information, measures can be taken — such as establishing consumption recommendations or maximum limits for these contaminants — with a wide margin of safety to ensure that the food is safe. That being said, these limits aren’t the same in all countries, as different criteria are applied in each jurisdiction.

Disparity of criteria: the case of the United States

In the U.S., there’s no federal legislation that establishes limits for the cadmium content in cocoa. That’s why the study in Consumer Reports used the toxicological standards laid out in California, where restrictions do exist. There, a maximum allowable dose level (MADL) of 4.1 micrograms per day of cadmium is considered acceptable, which is the exposure level at which it would have no observable effect on the reproductive system.

The researchers compared the results of their analyses with said reference value. They found that single servings of some chocolates (or 30 grams, approximately a third of a bar) already exceeded that limit, even by twice as much.

The authors of the study used California’s standard as a reference, because they considered it to be the most prudent. The state’s legislation — Proposition 65 — has already been in the news on several occasions. However, many experts consider that the caution expressed by the state is somewhat excessive. A similar debate occurred when the California state government wanted to mandate the inclusion of warning labels on coffee and soft drinks, due to their high acrylamide and 4-methylimidazole content. But these potentially toxic compounds are also produced naturally in everyday processes, such as when we toast bread, or when we heat sugar to make caramel.

Disparity of criteria: the case of the European Union

The Joint FAO/WHO Expert Committee on Food Additives (JECFA) defines a maximum tolerable intake of cadmium to be 25 micrograms per kilogram (2.2 pounds) of body weight per month. This means that a person who weighs 176 pounds could ingest about 67 micrograms in a day, without a danger to their health. This figure is far above California’s recommendation of 4.1 micrograms per day.

Based on this reference value, in 2021, the JECFA made a recommendation to the Codex Alimentarius Commission, which is responsible for establishing internationally-recognized standards and recommendations about food. The JECFA requested the adoption of new guidelines regarding maximum levels of cadmium in chocolate — specifically, 0.3 micrograms per kilogram for the category of chocolate with up to 30% cocoa and 0.7 micrograms per kilogram for chocolate with 30% to 50% cocoa content.

However, the European Union refused to adopt these limits. Instead, it opted to maintain those that it had already established in 2014 (which are more restrictive) in order to better protect the child population, which is the most vulnerable to these toxic components.

These 2014 guidelines were established based on the work of the European Food Safety Authority (EFSA), which established a tolerable weekly intake of cadmium at 2.5 micrograms per kilogram of body weight. That is, a 176-pound adult could ingest 28.6 micrograms in one day. Still, this is approximately seven times more than what is considered safe in California. Hence, had the study published in Consumer Reports used this as a benchmark upon conducting analyses, all chocolate would have been considered safe.

The difference in the reference values taken in one place or another is due — above all — to the criteria being considered. In California, the value of 4.1 micrograms per kilogram is based on a toxicological study carried out in 1986. The explanation is based on the principal danger of cadmium, which is damage to the reproductive system. In fact, the California guidelines are based on a person who weighs 128 pounds, which was the average weight of a pregnant woman 37 years ago.

However, in the EU, the acceptable amount of toxic compounds is based on more recent studies, from 2011, which consider that the main danger of cadmium is possible kidney damage. And, rather than considering women to be the most vulnerable population, the child population is classified as being the most at-risk group.

Generally, the higher the proportion of cocoa in chocolate, the more cadmium it contains. That’s why different limits are established, depending on the proportion of that metal.

The importance of origin

To understand the situation at an international level, we can consult the data collected by the WHO on contaminants in its “Food Contamination Assessment” application. According to the data available for Europe, in 2020, none of the samples analyzed exceeded the maximum limit of 0.8 micrograms per kilogram, while the vast majority of chocolate samples were between 0.1 and 0.3 micrograms per kilogram. However, in the data available for the U.S. in 2020, almost all the samples analyzed exceeded the limit of 0.8 micrograms, mostly reaching values of between one and two micrograms per kilogram.

It’s risky to draw a conclusion from isolated data, but it’s possible that the differences are explained by the origin of the cocoa. Cadmium — like lead — can be present in soil as a result of human activity, such as mining or heavy industry. But these types of metals can also come from natural sources, such as volcanic sediments. For this reason, cadmium levels are higher in cocoas from regions with volcanic activity — such as the Southern Cone of the Americas or the Southeast Pacific — than in cocoa beans that come from other places where this doesn’t occur, such as in West and Central Africa.

Hence it’s likely that the levels of cadmium in the cocoa used in the United States are higher than those of the cocoa that reaches the EU, given that America’s principal cocoa suppliers are Ecuador, the Dominican Republic and Papua New Guinea, in addition to Ivory Coast and Ghana. For the EU, the most important cocoa suppliers are Ivory Coast, Ghana, Nigeria and Cameroon.

In other words, the chocolate consumed in Europe isn’t the same as what’s consumed in the United States, nor are dietary habits or legislation. The results regarding cadmium and lead content cannot be applied across the board.

Lead in cocoa

With respect to lead, there’s also a disparity in criteria. The Codex Alimentarius sets a maximum limit of one microgram per kilogram of coca, a figure that the United States considers to be too high. In fact, for children, the FDA recommends a maximum limit of 0.1 micrograms of lead per kilogram of chocolate. That means that a single serving (30 grams) is considered safe if the lead content is capped at three micrograms — a far cry from the 0.5 micrograms per day set by California’s Proposition 65.

In the EU, no maximum limits are established for the lead content in cocoa. For various reasons, this contaminant is of less concern in chocolate than cadmium. It tends to be found at lower levels, given low bioavailability. European legislation focuses on foods that contribute the greatest amount of lead to the diet. This aspect is considered fundamental, because what’s most worrying about heavy metals is, above all, chronic toxicity, due to their accumulation in the body over time.

For example, if we talk about cadmium, the highest concentrations are found in algae, fish, shellfish and cocoa. However, foods that contribute the most to exposure via diet are cereals, vegetables, nuts and legumes, because humans consume more of these products. That being said, this doesn’t mean that we should worry.

No need to panic, but action should be taken

What we know today is that the chocolate and cocoa consumed in North America and Europe are safe and their cadmium and lead content doesn’t pose a health concern. Of course, food regulations aren’t written in stone. Changes in production, dietary patterns, or scientific knowledge can cause the limits for these heavy metals to change over time.

For the moment, health authorities are working with producers and exporters to take measures to reduce the levels of these contaminants in cocoa. This involves paying attention to the origin of beans, applying good production practices and other long- and medium-term actions, such as opting for younger plants, or trying to modify the composition of soil.

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