You Don't Need To Worry About Heavy Metals In Dark Chocolate

Why you probably don't need to stress about tiny quantities of lead and cadmium in your chocolatey treat.

Pictured: Yum. Photo by Mae Mu on Unsplash

Another week, another spate of scary headlines implying that you are going to be poisoned by the food you eat. There’s no more reliable story for media to tell about your health than the one that says that you’re unknowingly getting deadly chemicals in everyday products. I even wrote about this general trend last week.

This time, the story is about lead and cadmium infesting your dark chocolate. There’s no shortage of fearmongering stories implying that these sweet treats are contaminated with heavy metals, based on a new study that’s just been published.

Fortunately for all of us, the real risks here are incredibly low. As ever when it comes to stories about household products killing you, the devil is in the details, and the details show very little to worry about when it comes to eating dark chocolate.

Let’s look at the science.

The Study

The study in question was a fairly minimalistic effort by a group of scientists. The authors took 72 different chocolate bars purchased between 2014 and 2022, and sampled the levels of lead, cadmium, and arsenic in each of them. They classified risk according to the Californian Prop 65 limits which require labelling of products that have more than a certain amount of various substances in them - in this case, more than the Maximum Allowable Dose Level (MADL) for lead, cadmium, and arsenic.

Of the products tested, the average levels of lead and cadmium exceeded the MADL set by the Californian OEHHA, with 43% and 35% of products tested exceeding the MADL for lead and cadmium, respectively. Arsenic levels were universally lower than the MADL. The authors also found that the levels of heavy metals didn’t differ based on certifications, but that organic chocolate bars had significantly higher levels of cadmium when compared to non-organic.

Pictured: Deadly, apparently. Photo by Monika Grabkowska on Unsplash

What this means to the consumer is fairly simple - dark chocolate is probably entirely safe to eat, at least when it comes to lead and cadmium levels. In other words, pretty much the exact opposite of what most of the headlines have been saying.

There are a few reasons for this. Firstly, while the MEAN average levels of lead and cadmium exceeded the MADL, the MEDIAN levels were below this threshold. In other words, more than half of the sampled chocolates were below the MADL threshold. The authors don’t report how many samples tested negative for either lead or cadmium, but we know that at least a few had none of these metals detected at all.

Secondly, and more importantly, the MADL is intentionally too stringent. I’ve talked about this before - Prop 65 requires the Californian government to set thresholds that they are certain are safe. To do this, they take the known safe threshold for the most problematic source of exposure, and then divide that number by 1,000.

The lead MADL, for example, was set based on the lowest known safe level of lead inhalation. But you absorb somewhere around 5 times as much lead from inhalation as you do from food. So what the MADL represents is a number about 5,000 times lower than what scientists considered to be a safe dose of lead when setting the regulation.

There are complex reasons as to why the MADLs are set this way - it has to do with a negotiation between consumer safety and a desire to reduce the regulatory burden on businesses - but the upshot is that the MADL is not a useful threshold to use to determine safety.

In this particular study, the highest quantity of lead that the authors found in any chocolate bar was 0.3 micrograms per gram. Another way of saying this is 0.3 millionths of a gram of lead per gram of chocolate. So eating an entire 200g (7 ounce) bar of dark chocolate would be equivalent to eating 60 millionths of a gram of lead.

Or eating both of these Lindt bars at the same time. Not easy to do, they’re very rich. Photo by Moses Rukshan on Unsplash

And that’s if you eat a very large amount of chocolate on a daily basis. If you instead eat a few servings of the sweet treat a week, you’ll probably be falling well below the MADL even for these more contaminated bars. Moreover, there’s no evidence that even the highest level of lead exposure that this study found from any chocolate bar is harmful. In fact, the evidence that the MADL is based on suggests that eating 60micrograms of lead in a day is still well below the lowest level of lead exposure that’s known to cause any harm. And that’s the highest amount you could get if you were eating an entire bar of the most contaminated chocolate found in this study on a regular basis.

Bottom Line

Monitoring foods for safety is very important. There’s always a chance that you find very high levels of a pollutant in some products, and that sort of thing needs to be acted on very quickly to ensure that people don’t get very sick.

But the take-home from most of these studies that test for heavy metals is that the things you eat are generally very safe. Even using the most conservative threshold for lead and cadmium exposure that has been set anywhere in the world, most of these chocolate bars were entirely fine to eat. None of them exceeded the MADL for arsenic, which has barely been mentioned in the news reporting.

The levels of lead and cadmium in chocolate bars appear to be well below any cause for concern. You get about as much of these heavy metals from eating dried fruit, and no one writes headlines about that.

Dark chocolate isn’t a particularly healthy thing to eat - despite the bitter taste, it’s usually a very high-sugar, high-calorie treat - but neither is it especially bad. I wouldn’t worry at all about the heavy metal content of your delicious dark chocolate. The data shows that even the worst chocolate bars are still almost certainly safe to eat.