Heavy Metals in Cacao and Chocolate? How Polyphenols Help

For a while now, levels of heavy metals such as lead and cadmium in cacao and chocolate products reported as high compared to other foods have been among the biggest scares in the high flavanol cacao space. It is an undoubtedly important topic of discussion which has already led to positive change in the industry, with a standard of keeping up-to-date and publicly available test results being practiced in some form by almost every major brand. But while the fact of cacao’s natural absorption of lead and cadmium from the soil in which it is grown is not one that should be overlooked, it does not tell the entire story either.

The perception of cacao as a food particularly at risk of containing dangerously high levels of these metals seems less and less fair with an understanding of the often-undiscussed factors outside of the raw numbers which impact how they can actually affect the body. For those invested in truly being mindful of what they eat, studies that now show how foods with different nutrient profiles may be very different in terms of heavy metal risk even when their heavy metal content is comparable are just as important to understand. Read on to learn more:

If you have read Vital Purple’s other articles on the subject or done your own research already, you likely know that the levels of lead and cadmium in cacao products are not due to some industrial process carelessly allowing them to be mixed in. In fact, as mentioned already, cacao’s heavy metal content is quite natural, being absorbed from the soil in which it is grown. The volcanic soils found throughout Latin America, while some of the most fertile on Earth, have the side effect of containing these substances that plants there take in small amounts of. 

For thousands of years now, cacao has been safely cultivated and consumed in these same regions by many different cultures.^[1] This is not to say that organic and high flavanol brands should be exempt from scrutiny, of course, but those which practice single-origin sourcing and remain transparent about their manufacturing process are likely already being as safe as they can. The nature of providing such a product means every batch will be different, grown differently in different soil in a different area, and the variance seen in heavy metal test results of major brands is largely due to this fact.

Also important to know is who is at greater risk of heavy metal exposure, with substances generally being much less dangerous to adults due to a lower consumption-to-weight ratio and developed bodies absorbing less of them in the first place. And given that cacao is now one of the most scrutinized foods for heavy metal content, you can freely read the relevant test results on most major brands’ sites and compare them with competitors and most national-level guidelines to verify product safety for yourself. 

Key Takeaways:

• Heavy metal content in cacao is natural due to absorption from fertile, volcanic soil

• Variance of heavy metals is in the nature of cacao batches kept minimally-processed

• Major cacao brands are now almost all very transparent about heavy metal results

Why have some of these laws been created such as Prop 65, MADL, and the EU laws dictating the heavy metal content that is allowed to be consumed from cacao? Well, unfortunately the heavy metals in cacao are known to be bioavailable. However, what's not taken into account is serving size per person based on the body weight of the recipient and that person's ability to recycle heavy metals from their body based on their immune system and diet. 

Now, we'll discuss why the bioavailability of metals like cadmium in cacao are not as important as you may think because of the polyphenols in cacao. 

The simple amount of heavy metals present in a food is not the only factor in determining its potential toxicity, however. How able they are to be absorbed by and therefore affect the body, a measure known as bioavailability, is often just as important to look at. The bioavailability of a food’s heavy metals may be entirely different depending on its nutrient profile, a fact that becomes relevant in cacao due to its high polyphenol concentration. Polyphenols are a large group of antioxidant-rich micronutrients of which cacao flavanols are just one type, and current-day research consistently suggests their ability to protect against bodily absorption of metals like lead and cadmium when consumed.

Specifically, a 2018 report in the journal Current Drug Targets cites structures within polyphenols that form complexes with these heavy metals. These complexes are then unable to be absorbed by the stomach and intestines in the way metals typically would, and are eliminated more quickly from the body as waste instead.^[2] 

Other research cites magnesium, a mineral cacao is very naturally rich in, as a good inhibitor of both lead and cadmium as well.^[3][4] Important to note is that none of these studies claim zero net absorption of heavy metals is possible by consuming magnesium and polyphenol-rich foods, rather showing reduced effects of what are already considered by most jurisdictions to be safe levels of these chemicals.

Key Takeaways:

• Polyphenols in cacao help offset the absorption of dietary heavy metals

• Cacao is also rich in magnesium, which may help offset the same metals

• No study claims zero net absorption, but a lesser effect of levels already considered safe

Why specifically are polyphenols able to form new complexes with the heavy metals?

• Phenolic hydroxyl groups (–OH): Polyphenols are rich in aromatic rings with several –OH groups. When these groups deprotonate (lose H⁺), the oxygen atoms become negatively charged and highly attractive to positively charged metal ions such as Pb²⁺, Cd²⁺, or Fe³⁺.

• Ortho‑dihydroxy and catechol motifs: When two –OH groups sit next to each other on the ring (ortho position, often called a catechol unit), they can wrap around a metal ion in a five‑ or six‑membered ring, forming especially stable “chelate” complexes.

Why this favors heavy‑metal binding

• Hard‑Lewis‑base oxygen atoms capture hard‑Lewis‑acid metal ions (like Fe³⁺, Cu²⁺, Al³⁺) through strong coordination bonds, effectively “locking” them into the polyphenol framework.

• The resulting ring‑like coordination geometry (often five‑ or six‑membered rings) is thermodynamically stable and reduces the metal’s availability for harmful redox reactions or absorption in the gut, which is why polyphenols can help mitigate heavy‑metal toxicity.

The Unfortunate Caveat:

• With polyphenols able to form new complexes with heavy metals, forcing them to be less absorbable into the body- this also applies with good minerals as well. Minerals and polyphenols can help the body recycle heavy metals, but polyphenols can bind to minerals such as Iron and Zinc, so they're less digestible as well. That's why it's important to have a mineral rich diet at all times, because there are plenty of foods that can deplete your body of minerals accidently. 

Where does that leave us within the dangers heavy metals from cacao being absorbed into the body? Well, we can know that high flavanol cacao will likely reduce the likelihood of these heavy metals being absorbed into your body. What about cacao with little polyphenols? Where would you find cacao? Unfortunately that is all modern cacao and chocolate. High temperature roasting and processing strips high flavanol cocoa and chocolate of their (sometimes) natural polyphenols. Now...one would come to the next conclusion...without the polyphenols are these heavy metals more likely to absorb into my body? In theory- The answer is yes. Without the cacao polyphenols to bind to these heavy metals and create new unabsorbable complexes that your body can easily recycle, you would be in more danger of absorbing heavy metals from cocoa into the body. 

Today, cacao is almost certainly one of the most scrutinized foods for potential heavy metal content, largely owing to the natural ways it can accrue small amounts of these substances as we have already discussed. Important to note however is that multiple other foods have naturally high heavy metal levels while not carrying the same natural inhibitors as cacao, and still receive less of a spotlight.

One particularly interesting example of this is rice. Like cacao with lead and cadmium, rice, especially brown rice, has an increased ability to absorb arsenic from the soil in which it is grown.^[5] Brown rice may still offset some of this by being a great source of magnesium like all other whole grains, but what it does not have versus cacao is anywhere near the same polyphenol content. Other foods like spinach and lettuce also absorb lead and cadmium from the soil, but being leafy greens, these will have that high polyphenol content to help offset some of it.

Rather than simply replace one food scare with another, however, the point here is to show that a concern about heavy metals in food should not single out cacao as its biggest or only target. Transparency about what goes into our food is very important, and the spotlight on cacao has largely made it a reality. 

Key Takeaways:

• Natural heavy metals in rice are likely more dangerous than those in cacao

• Other foods like spinach and lettuce contain the same natural heavy metals as cacao

• Cacao is more transparent than other foods on heavy metals due to scrutiny

So why are there heavy metal standards without the proof that heavy metals in cocoa increase heavy metals in the body? Why have we removed the burden of proof from our governing bodies when there is a lack of substantial evidence that heavy metals found in cacao substantially increase heavy metal load in the body?  

Why is this bad? Because it limits great pure cacao from being consumed. Heavy metals are somewhat unpredictable in cacao and when cacao tests high for heavy metals, there is nothing you do with the material except dilute it. Are there nefarious intentions around these laws, in an attempt to negotiate more effectively with cocoa producers? The argument can definitely be made unfortunately. 

The best to safely consume cacao and avoid any uptake in heavy metals is to do two things. Watch out for cacao that closely monitors their cacao source for heavy metals, and look for cacao brands that are in high in polyphenols that naturally help your body recycle these heavy metals effectively.

Which high flavanol cocoa brands actively test for heavy metals and in theory are the safest to consume? You can see our list here! (Hint Vital Puprle can be found on that list ) 

Sources:

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC10920634/ 

2. https://pubmed.ncbi.nlm.nih.gov/29611487/

3. https://pubmed.ncbi.nlm.nih.gov/2397164/

4. https://pubmed.ncbi.nlm.nih.gov/9884986/

5. https://pmc.ncbi.nlm.nih.gov/articles/PMC7745115/

https://pmc.ncbi.nlm.nih.gov/articles/PMC10452320/

https://www.bohrium.com/en/paper-details/the-interactions-of-polyphenols-with-fe-and-their-application-in-fenton-fenton-like-reactions/817058263399923716-3821

https://pubmed.ncbi.nlm.nih.gov/29611487/

https://www.sciencedirect.com/science/article/abs/pii/S1383586622013867

https://www.bipcic.icpm.tuiasi.ro/pdf/2018/3/bipi_cic_2018_3_02.pdf

https://www.sciensano.be/sites/default/files/vanderschueren_et_al_2023_cacao_consumption_and_cadmium_exposure.pdf

Writer / Researcher: Trey Norbey