Most people would probably agree that dark chocolate is a healthier candy. It is known for its flavanol content1Impact of cocoa flavanols on human health | Martin, M.Á., Ramos, S. | 2021 | Food Chem Toxicoland a lower amount of sugar compared to milk chocolate. But is dark chocolate really as healthy as it is thought to be?
In this article, we’ll look at a known yet under-discussed issue of heavy metals—specifically, lead and cadmium—in dark chocolate and attempt to answer the question—how bad is the problem?
To get the full picture on the matter, we’ll first need to answer the following questions:
- How much lead and cadmium can you find in your average dark chocolate bar?
- How does this stack up against the everyday exposure we “normally” get to these substances?
This is because we are inevitably exposed to lead and cadmium daily, so we need to understand how much extra we might be getting from our dark chocolate fix. After all, it’s “the dose makes the poison,” as a popular adage goes.
What are lead and cadmium, and why are they toxic?
Lead and cadmium are toxic heavy metals that occur naturally in the Earth’s crust. While they are naturally released into the environment through the process of erosion, the main source of these metals are human activities, such as mining, burning fossil fuels, manufacturing, and use of pesticides and fertilizers.
Lead and cadmium are listed in the second and seventh positions respectively of the Harmful Substances Priority List (HSPL), which ranks substances based on their potential threat to human health.
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Both metals have been found to be associated with a number of adverse health effects, even at low levels of exposure.
Cadmium is classified as a Group 1 carcinogen by The International Agency for Research on Cancer (IARC). Its toxicity has been demonstrated2Cadmium Toxicity and Treatment | Bernhoft, R.A. | 2013 | The Scientific World Journalin several organs, but it most often causes damage to kidneys, liver, and bones.
Lead is a neurotoxin3Neurotoxic effects and biomarkers of lead exposure: a review | Sanders, T., Liu, Y., Buchner, V., Tchounwou, P.B. | 2009 | Rev Environ Healththat is especially harmful during children’s development, causing changes in the brain that lead to lowered IQ, perception and concentration problems, and hyperactivity. The IARC also classifies lead as Group 2A or a “probable human carcinogen.”
Where does the lead and cadmium in chocolate come from?
Although most consumers are unaware of the high concentrations of lead and cadmium in dark chocolate, it is actually a very well-known problem in the chocolate industry. According to a study by the FDA, dark chocolate has the third-highest levels of lead and cadmium among more than 300 other foods, exceeded only by baking powder and cocoa powder for lead, and cocoa powder and sunflower seeds for cadmium.
The levels of lead and cadmium are higher in dark chocolate than in milk chocolate because dark chocolate contains more cocoa solids, the part of the cacao bean where these metals are found.
But how do lead and cadmium get into cacao beans in the first place?
Cadmium contaminates cacao beans much like it does other plants—through the soil, absorbed by the cacao tree’s roots. How much cadmium accumulates in cacao beans depends on the soil’s initial contamination and the age of the cacao tree from which they are harvested (the older the tree, the more cadmium). Cadmium can also enter chocolate during production— through added ingredients, primarily milk4Lead and cadmium blood levels and transfer to milk in cattle reared in a mining area | Chirinos-Peinado, D.M., Castro-Bedriñana, J.I. | 2020 | Heliyon.
Lead, on the other hand, contaminates cacao beans during processing. Typically, cacao beans dry out in the sun after being harvested. The drying process ferments the beans, which develops their chocolate flavor. As they dry on the ground, their shells come into contact with lead-contaminated soil—the by-product of the decades of use of leaded gasoline in cocoa-producing countries. The sticky coating of freshly harvested cacao beans allows the lead from the soil to easily cling to their shells. Then, during bean processing, the lead on their shells is transferred to cacao nibs (the center), and finally to the chocolate liquor produced from nibs.
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How much lead and cadmium is in dark chocolate?
There isn’t a definite range of lead and cadmium in dark chocolate, but some studies attempted to shed light on the matter.
In December 2022, a study by Consumer Reports, an American nonprofit organization that conducts independent product testing, tested 28 dark chocolate bars for lead and cadmium.
Since there are no federal regulations for these metals, the study used California’s MADL (maximum allowable dose level) as a reference. This standard sets the daily MADL for lead at 0.5 micrograms and for cadmium at 4.1 micrograms.
The results were concerning:
- Eight bars contained over 100% of the MADL for cadmium in a one-ounce serving (28g).
- Ten bars exceeded the MADL for lead per ounce.
- Five bars exceeded the MADL for both lead and cadmium.
In terms of micrograms, the lead content ranged from 0.07 µg to 1.325 µg per one-ounce (28g) serving, with an average of 0.6 µg. The cadmium content per one-ounce serving varied from 1.025 µg to 10.373 µg, with an average of 4.1 µg. See calculations here.
It’s worth noting that the CR study’s sample was quite small, and that the research wasn’t peer-reviewed. However, the results show similar levels of lead and cadmium found in the large study5Cadmium and lead in cocoa powder and chocolate products in the US Market | Abt, E., Fong Sam, J., Gray, P., Posnick Robin, L. | 2018 | Food Additives & Contaminantspublished by researchers at the Food and Drug Administration in 2018. According to that study, an average one-ounce (28g) serving of dark chocolate contained 0.8 µg of lead and 7.6 µg of cadmium, with certain products having three to four times higher levels of these metals.
Similar levels of lead and cadmium in dark chocolates were also reported by As You Sow, which has been testing chocolate products available for sale in California since 2014. Similarly by Consumer Lab (results behind paywall, unfortunately).
How much lead do we “normally” consume per day?
Lead is present in the soil, air, and water. There are also still some consumer products (e.g. children’s toys, jewelry) made with lead both in the U.S. and in other countries. Finally, lead is present in our food, most notably leafy greens, root vegetables, and dried spices.
Because lead is so ubiquitous, everyone inevitably comes into contact with it on a daily basis. However, due to natural variation across the world, it’s quite difficult to estimate just how much lead an average person consumes daily.
The World Health Organization (WHO) estimates mean lead exposure per day by country, but it varies greatly. For the source, see table 22 of this report.
Based on these estimates, we could assume the following ranges for a 70 kg human.
| Country | Mean exposure per day (mcg/kg bw) | 70 kg human |
| Australia | 0.02 – 0.40 | 1.4 – 28 mcg / kg |
| Canada | 0.11 | 7.7 mcg / kg |
| China | 0.9 | 63 mcg / kg |
| Europe | 0.36 – 1.24 | 25.2 – 86.8 mcg / kg |
| India | 0.44 | 30.8 mcg / kg |
| New Zealand | 0.13 | 9.1 mcg / kg |
| USA | 0.03 | 2.1 mcg / kg |
Another source is a study in Northern Italy6Lead exposure in an Italian population: Food content, dietary intake and risk assessment | Malavolti, M., Fairweather-Tait, S.J., Malagoli, C., Vescovi, L., Vinceti, M., Filippini, T. | 2020 | Food Research Internationalthat found that people there consumed 0.155 µg/kg of bodyweight per day. So, a 70kg human would consume 10.85 µg per day.
These figures suggest that daily lead exposure below 10 µg might be considered low, while 10-20 µg might be considered “normal” for developed countries.
How much cadmium do we “normally” consume day to day?
The general population is mostly exposed to cadmium through cigarette smoking (including passive smoking) and food. Numerous studies found cadmium in coffee, fruits, and green, leafy vegetables. A study published in 2021 in Consumer Reports also found it in many commonly used dried spices.
Below are a range of values for average daily cadmium consumption from the WHO report mentioned previously:
| Country | Mean Exposure per month (mcg/kg bw) | Mean Exposure per day (mcg / kg bw) |
| Australia | 2.2 – 6.9 | 5.13 – 16.1 |
| China | 9.9 | 23.1 |
| Europe | 9.1 – 12.1 | 21.2 – 28.2 |
| USA | 4.6 – 8.1 | 10.7 – 18.9 |
Again, we could say that amounts less than 10 µg per day might be considered low, and amounts that fall in the range of 10 – 20 µg per day might be considered “normal” for developed countries.
Could eating 1 serving of dark chocolate per day be bad for our health?
To quantify the impact that a one-ounce serving of dark chocolate will add to your daily lead and cadmium exposure, we have to generalize, and accept that it’s guaranteed to inaccurate, but ideally is within an order of magnitude accuracy (less than 10x difference in either direction).
To start with, we will use the above figure of there being 0.6 µg of lead and 4.1 µg of cadmium, on average in a one-ounce (28g) serving of dark chocolate (data calculated from the Consumer Reports study).
Next we will assume 10 µg of lead and cadmium exposure per day. This may be high for some areas, but low for other areas.
Using these assumptions we can speculate that one ounce of dark chocolate may increase lead exposure by 6% and cadmium by 41% per day.
To give one further example, if we were to use the figures quoted by WHO for the USA of 2.1 mcg of lead and 10.7-18.9 mcg of cadmium, then a one-ounce (28g) serving of dark chocolate may raise daily lead exposure by 28% and cadmium by between 21 and 38%.
Fortunately, our bodies are remarkably resilient when it comes to warding off the host of harmful substances we come in contact with on a daily basis, including heavy metals.
So, given that you’re already exposed to lead and cadmium on a daily basis, eating a little dark chocolate every now and then is unlikely to pose a significant risk. With a caveat that pregnant women and developing children are more at risk from the harms of heavy metals.
However, eating dark chocolate is potentially an issue if you are eating a lot of it regularly. So, if that’s the case, consider cutting back. If you can’t resist, you could at least try opting for dark chocolate brands that claim to contain less lead and cadmium, although it’s not a foolproof measure.
Which brands can we trust?
Unfortunately, there are no (at least, to our knowledge) chocolate brands that consistently conduct batch testing for lead and cadmium. However, there are a few that conduct partial testing.
For example, the German company Edelmond appears to test for cadmium.
If you’re after the health benefits of flavanols found in chocolate, you may consider checking out the supplement brand CocoaVia (for 20% off, you can use this coupon code). Their products are made with their proprietary Cocoapro™ cocoa extract, which is made in a way that does not lead to a concentration of lead and cadmium – or so they claim.
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Can we trust the brands that had lower levels when tested?
While most of the chocolate bars tested in the above studies were found to contain potentially toxic amounts of lead or cadmium (or both), some brands did show lower, potentially safe levels. So, it’s only natural to ask; can we trust these “safer” brands?
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The hitch here is that the levels reported in these studies might not be the whole story. Why? Because the studies typically test only one batch of each chocolate brand. For all we know, the tested batches of some of the chocolates were OK, but it could just be luck.
Also, it’s worth noting that none of the chocolate brands tested in these studies actually test their batches for lead and cadmium. So, trusting the “safer choices” is still a bit of a gamble.
Is there a cover-up?
With the global chocolate market worth over $110 billion annually, there is, of course, a possibility of a cover-up. However, the results of the Consumer Reports study and As You Sow analysis are likely accurate as they were conducted by reputable nonprofits.
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However, when it comes to reports of lead and cadmium levels by chocolate brands themselves, you should probably take those with a grain of salt.
How does this get fixed going forward?
There are two potential avenues for addressing the issue of lead and cadmium in chocolate:
1) Regulatory Action: Regulators could set low maximum thresholds for lead and cadmium per serving in chocolate and actively enforce these rules.
2) Consumer Awareness: If consumers become more informed about this issue, they may shift their preferences toward brands that conduct batch testing and strive to maintain low heavy metal levels.
To tackle the problem at its root, chocolate manufacturers must gain a thorough understanding of their supply chain processes and figure out how to bring lead (during processing) and cadmium (during growing) down.
For example, one way the concentration of cadmium can be reduced is by blending beans harvested in higher-cadmium regions with beans harvested in lower-cadmium regions, which will lower cadmium concentration in the final product. Some manufacturers are already doing that.
Cacao growers could also work on increasing soil pH to reduce cadmium uptake or replacing contaminated cadmium-contaminated soil altogether. As a more enduring solution for cadmium in chocolate, we could genetically engineer cocoa plants to absorb less cadmium from the soil, but it could take up several years.
For lead, manufacturers can minimize contact between beans and soil during drying (e.g. by drying beans on elevated surfaces or covering them with protective covers), improve processing and cleaning equipment, and implement rapid lead testing kits and soil analysis.
Closing words
In conclusion, while dark chocolate is probably safe as an occasional treat, it’s useful to be aware of the heavy metal presence and make your health decisions accordingly.
If you’ve any questions or comments, please leave them below.
References
- 1Impact of cocoa flavanols on human health | Martin, M.Á., Ramos, S. | 2021 | Food Chem Toxicol
- 2Cadmium Toxicity and Treatment | Bernhoft, R.A. | 2013 | The Scientific World Journal
- 3Neurotoxic effects and biomarkers of lead exposure: a review | Sanders, T., Liu, Y., Buchner, V., Tchounwou, P.B. | 2009 | Rev Environ Health
- 4Lead and cadmium blood levels and transfer to milk in cattle reared in a mining area | Chirinos-Peinado, D.M., Castro-Bedriñana, J.I. | 2020 | Heliyon
- 5Cadmium and lead in cocoa powder and chocolate products in the US Market | Abt, E., Fong Sam, J., Gray, P., Posnick Robin, L. | 2018 | Food Additives & Contaminants
- 6Lead exposure in an Italian population: Food content, dietary intake and risk assessment | Malavolti, M., Fairweather-Tait, S.J., Malagoli, C., Vescovi, L., Vinceti, M., Filippini, T. | 2020 | Food Research International
Disclaimer: The above information is for research and educational purposes only and not a substitute for professional medical advice. See full medical disclaimer.
