Chocolate (part 1)
I don't know who first harvested, fermented, dried, and roasted the seeds of the cacao tree, but whoever you are, thank you. You did good.
For a long time we've treated chocolate as a mixed blessing. It can be bad for you (lots of fat and sugar), but it's good for you too (lots of antioxidants). Over the past couple of months, the stakes have gotten higher. New evidence confirms that some chocolate contains high levels of lead and cadmium, yet the flavonols in it may actually promote heart health. The bad news seems worse than it used to be, even as the good news looks better than ever.
This newsletter is the first of a two-part look at the latest evidence. My focus this week is on whether the bad news about lead and cadmium is as bad as it sounds. (Spoiler alert: It's not.) Next week I'll talk about the good news. (Spoiler alert: It might be slightly better than the FDA suggested earlier this month.)
The bad news
Dave Barry once joked that "your hand and your mouth agreed many years ago that, as far as chocolate is concerned, there is no need to involve your brain". I would've agreed, before I learned that dark chocolate contains heavy metals. The brain definitely needs to join this party.
Back in December, Consumer Reports published an investigation showing that 23 of the 28 dark chocolate bars it tested have concerning levels of cadmium and/or lead, two metals that can accumulate in the body and cause damage. This is consistent with earlier findings and has sparked at least one lawsuit, against Hershey.
Scary, right? As a fan of dark chocolate, I was tempted for a moment not to look closely at the data. After all, there's so much unhealthy gunk in our food...why single out one of the most delicious and comforting things one could eat? The thought that dark chocolate may be toxic just made me want to curl up with a bar of dark chocolate.
I looked at the data anyway, and I'm happy to report that the news isn't quite as bad as it sounds. You can eat dark chocolate safely. You may want to take some simple precautions though.
Why pick on dark chocolate?
Cacao trees, the source of the beans (i.e., seeds) used to make chocolate, draw cadmium from the soil, while lead contamination occurs during processing steps such as harvesting, drying, and fermentation. Most of the lead and cadmium that make their way into chocolate are pollutants rather than naturally occuring. Dark chocolate tends to have more of each metal than milk chocolate because it's higher in cocoa solids.
Consumer Reports findings
Consumer Reports classified each brand of dark chocolate they reviewed as either safe or not with respect to lead and cadmium. The cut-off values were California's Maximum Allowable Dose Level for each metal (0.5 micrograms per ounce for lead, 4.1 micrograms per ounce for cadmium). By these standards, only five brands were deemed safe. Eight brands exceeded California's maximum for cadmium, ten exceeded the maximum for lead, and five exceeded the maximums for both. (You can see the results for all 28 brands here.)
Before you start selectively throwing away chocolate bars, let's take a closer look at the data.
The California standards
California's Maximum Allowable Dose Levels (MADLs) are more stringent than any other state's. In fact, these cut-offs fall substantially below the safe levels suggested by recent studies.
To calculate their MADLs, researchers at California's Office of Environmental Health Hazard Assessment identified the highest amount of lead (and, separately, cadmium) that any single study has found to not be harmful. The researchers then divided that amount by 1,000 "in order to provide an ample margin of safety". In other words, the California standards set limits of one one-thousandth of the maximum known safe levels for each metal.
Those maximum known safe levels could've been divided by some other number, such as 460, or 803, and we'd still have an "ample" margin of safety, but 1,000 is a nice round number, and it's enormous. If I lived in California, I would appreciate this extreme cautiousness around food safety. But it raises a question: What does the actual data tell us about exposure to low levels of lead and cadmium?
Actual safety data
One-time exposures to relatively high levels of these metals (e.g., in foods) are not typically harmful. Dark chocolate could only be toxic if you ate enough of it, for a long enough period of time, that either or both metals accumulate and remain in your body. So, assuming that you ate it every day, how much could you safely eat?
The most conservative approach to this question is to consider safe daily consumption for children and fetuses (via their mothers), since they're especially susceptible to the effects of heavy metals. What's safe for them will be safe for healthy adults.
Lead
Exposure to lead is primarily measured by its presence in the bloodstream. The WHO, the CDC, and other organizations concur that no safe blood lead levels in children have been identified. This doesn't mean that safe levels don't exist. It simply means we haven't identified a precise cutoff, if there is one.
Since 2021, the CDC has used a cutoff of 3.5 micrograms per deciliter of blood to mark the point at which intervention is needed. This is not a toxicity threshold, but rather the value above which 2.5% of American children now fall. Very few studies even hint that levels this low might be harmful, but in the interest of caution, and in order to prioritize those who need support, the CDC chose this conservative value.
To achieve that 3.5 micrograms/dL level, the FDA estimates that a child would need to ingest 2.2 micrograms of lead per day. (For a fetus, the mother would need to ingest 8.8 micrograms per day.)
In CR's data, the brand of chocolate with the most lead is Hershey's Special Dark Mildly Sweet Chocolate, which has 265% of the California Maximum Allowable Dose Level, or 1.325 micrograms. Assuming that this value remains constant from one Hershey's bar to the next, a child could eat up to about 1.6 ounces of this chocolate per day and stay within the CDC/FDA limits. A pregnant woman could eat up to about 6.6 ounces per day.
So, assuming the most vulnerable dark chocolate-eaters, and the worst chocolate (among the brands CR investigated) a small amount of daily consumption would still not exceed conservative limits set by the CDC/FDA. Meanwhile, there's a lot of variability in the lead content of the other brands that CR reviewed. Hershey's Special Dark Mildly Sweet Chocolate, for example, has about 19 times more lead in it than Mast Organic Dark Chocolate. Assuming you're not pregnant, you could eat 7 ounces of Mast per day and still not exceed the exceptionally stringent Californial MADLs. According to the CDC/FDA calculations, a child could eat just over 30 ounces of Mast per day without exceeding the 3.5 microgram/dL limits. (Please don't give your child this much chocolate!)
I don't mean to sound casual about food safety. Lead has a long, dark history of undermining public health, and, as the Flint water crisis illustrates, it remains a dangerous pollutant. My point here is simply that dark chocolate may not pose a special risk – and it almost certainly does not if you're mindful of which brand you choose, how often you eat it, and how much you eat.
Sad to say, we're all exposed to trace amounts of lead in food, air, water, soil, and commercial products. If you eat dark chocolate regularly and have concerns, you can consult the Consumer Reports guide, or see more comprehensive (but older) data at As You Sow. I suspect most of us have no genuine cause for concern.
Cadmium
Experts disagree about the cut-off for safe levels of cadmium exposure, so I will assume the MADL limit set by California (4.1 micrograms/dL). which is more stringent than what's used by other organizations such as the EPA (6 micrograms/dL), the U.S. Agency for Toxic Substances and Disease Registry (6 micrograms/dL), and the European Food Safety Authority (21 micrograms/dL).
California's MADL for cadmium is based on one study, with rats, that estimates .07 milligrams/dL per kilogram of body weight as the highest level that causes no harm. To obtain the 4.1 micrograms/dL MADL, the researchers assumed a 58 kg pregnant woman, and, as I mentioned earlier, divided by 1,000 to provide an enormous margin of safety. (The value for a child who just turned 3 and weighs 30 pounds would be slightly higher at 5.15 micrograms/dL.)
To illustrate how conservative it is to divide the observed maximum safe amount by 1,000, consider the following statement from the U.S. Agency for Toxic Substances and Disease Registry (ATSDR):
"Although human data are preferred, MRLs [minimum risk levels] often must be based on animal studies because relevant human studies are lacking. In the absence of evidence to the contrary, ATSDR assumes that humans are more sensitive than animals to the effects of hazardous substances [and] that certain persons may be particularly sensitive. Thus the resulting MRL may be as much as a hundredfold below levels shown to be nontoxic in laboratory animals."
In other words, the maximum safe levels identified in animal studies could be as much as 100 times greater than they are for humans. You might therefore want to divide the maximum observed safe levels by 100 or more. California divides by 1,000.
Again, I'm not complaining about California's restrictiveness. I would want all public health organizations to err on the side of safety. I'm just suggesting that the margin of error seems enormous.
In CR's data, five of the 28 brands of dark chocolate have safe levels of cadmium as well as lead. An additional 10 brands have safe levels of cadmium. Although these 10 brands exceed the California limits for lead, they don't necessarily exceed the CDC/FDA safe levels. For instance, a child could eat roughly 3 ounces per day of four of those 10 brands and still come in just under 2.2 micrograms for lead (and be safe under either standards for cadmium).
Conclusions
1. Large amounts of dark chocolate, consumed occasionally, should not be toxic.
You could not eat enough chocolate at one sitting to attain toxic levels of lead or cadmium. If there's cause for concern, it's that regular consumption of dark chocolate – large quantities of certain brands – might allow these metals to accumulate. (As far as I can tell, it's not possible to define "regular consumption" or "large quantities" very specifically.)
2. Small amounts of dark chocolate, even if consumed every day, should not be toxic.
The definition of "small" depends on your body weight, your developmental status (adult, child, fetus), and the brand of chocolate. The Consumer Reports data provides the most conservative guidelines, as do those from As You Sow, which also rely on California standards. Meanwhile, CDC/FDA calculations provide guidelines that are also conservative but more consistent with existing data. Several ounces per day of most brands would be quite safe according to that data.
Should you be concerned about metals in chocolate adding to what you ingest from other sources? Probably not. The only consumables that tend to have more lead than chocolate are cocoa powder and baking powder, while the only ones that have more cadmium are cocoa powder and sunflower seeds. Other foods typically have much less, although specific occupations and activities can increase exposure (e.g., making stained glass, eating certain candies from Mexico, and using certain brands of turmeric from India or Bangladesh may increase ingestion of lead) .
At the same time, other elements in your food can work against the absorption of lead and cadmium. Here's how Johns Hopkins Medicine toxicologist Andrew Stolbach puts it:
"The safety levels for lead and cadmium are set to be very protective, and going above them by a modest amount isn't something to be concerned about...If you make sure that the rest of your diet is good and sufficient in calcium and iron, you protect yourself even more by preventing absorption of some lead and cadmium in your diet."
3. Brands of dark chocolate vary widely in their heavy metal content.
If you eat dark chocolate regularly and still have concerns, you can check the Consumer Reports or As You Sow lists, or use the CDC/FDA calculations provided here, and decide which brands are right for you. You'll have a lot of options.
Finally, if you'd like to push manufacturers to reduce the amount of heavy metals in their chocolate, you can digitally sign Consumer Reports' petition to the makers of the five bars with high levels of both lead and cadmium, and/or reach out to As You Sow.
Now that I've finished, I'm going to open this Ghirardelli Intense Dark chocolate bar on my desk. 3.5 ounces of joy, and I'm pretty sure it's safe.
Thanks for reading!