Should you judge these chocolates based on:
- TASTE – delicious or not?
- SUGAR – how many sugar grams is this adding to your day?
-
METAL– read on to avoid being fooled by headlines.
Having been asked my perspective on this many times, I hope this article answers open questions. Consumer Reports (CR) published a news article with results from their testing of 23 chocolate bars for metals. Read further to decide for yourself whether you should care or not and why.
What is missing from this?
What do these %s refer to?
You must go to CR’s ‘Methodology’ sheet (it would be helpful to have a more comprehensive Methodology, and the actual test results data, but at least you can see what the %s refer to): No, these %s do not refer to US regulatory benchmarks for Cadmium (Cd) levels in chocolate or food products, as there are none. The %s are in comparison to California’s Proposition 65 determination of a “Maximum Allowable Daily Level” (MADL), which is 4.1 micrograms (µg) for Cd.
- This 4.1µg per day comes from calculations made by the California Office of Environmental Health Hazard Assessment (OEHHA) based on one rat study in 1986.
- The Study: Gestating rats were given freely in drinking water either 4.2µg/ml (ppm) or 8.4µg/ml (ppm) concentration of Cadmium Acetate throughout their pregnancy. Result? “The metal exposure had no effect on the ontogeny of physical landmarks, surface and air righting reflexes and visual placing, but a significant hyperactivity and delay in the development of cliff aversion and swimming behavior were observed in the neonatal pups of either treatment group. Marked decreases in the locomotor activity shuttle box performance were evident at 60 days but not at 90 days of postnatal life. The apomorphine-induced hyperactivity was not affected in these rats at either age.”
Is it valid to translate this study to any relevance for humans eating food?
a) Cd Acetate is NOT found in nature. It is an industrial compound used for electroplating, semiconductors, textile dyes, and ceramics glazing.
b) What do we absorb from what is in a food? Cd (as with other metals) is less bioavailable (how much gets absorbed by the body) if it is in a food matrix vs. dissolved in drinking water. What factors impact the bioavailability of Cd?
- Food vs. Liquid
- Compound Form it is in
- Your Iron Status and Consumption: If you are not deficient in Iron, bioavailability for Cd will be lower. If the food you are eating contains Iron, it uses the same metal transporter protein 1 (MTP1) that the Cd would have used to be absorbed. What is one food that is high in iron? Dark Chocolate.
- Other Minerals: If you have sufficient iron, zinc, magnesium and calcium, there will be less absorption of Cd and lead (Pb), and more protection vs. these metals.
- Your Epithelium and Microbiota: Metalloids are stopped by epithelial cells (the cells that make up your intestinal wall), and by the microbiota lining the epithelial cells, providing a natural barrier. Additionally, microbiota also prevent metalloid entry by various reactions: adsorption, complexation and precipitation.
A study by Bolan S. et al (2021) provided a time course of metalloid transport through intestinal cells and discussed how the microbiota help prevent metalloid absorption. In this graph, Cd is the grey line and Pb is the blue line. As = Arsenic, Hg = Mercury, Cd = Cadmium, Pb = Lead.
3. Assuming one judges the 1986 rat study can be relevant to humans eating food, we will now look at the very interesting part of this – the CALCULATION for Prop65 MADL. The rats had free access to the Cd Acetate spiked drinking water, and the average daily Cd acetate intake apparently was 0.705mg/kg body weight/day. Prop65 authors took that 0.705mg and divided it arbitrarily by “10” to reach what they assumed will be a “No Observable Effect Level” (NOEL) of 0.07mg/kg body weight. They then multiplied this by an “assumed body weight of a pregnant woman”: 58kg. It is not clear if this is an average body weight of a pregnant woman, but that is the number chosen. Thus, they calculated: 0.07mg/kg x 58 = 4.1mg per day.
4. THEN, they arbitrarily divided this by an additional “1,000”, to reach their MADL of 4.1µg per day. To be clear, the gestating rats drinking Cd Acetate were drinking on average >76x this amount daily, and in the form of Cd Acetate in liquid. Do scroll up to reread the quoted effects of this.
How valid is this calculation? I support health protection and believe passionately in improving the food environment that we live in, but this type of approach does not help. It makes one question everything in Prop65, undermines food regulation further, and is a distraction from the most consequential issues in our food environment, i.e. excess sugar exposure.
Thus, this is the information that is missing from the CR image: The %s shown are in comparison to 4.1µg per day as ‘calculated’ by Prop65, not a government regulated amount – an amount that was reached through an arbitrary division upon division, starting from an animal study with minimal relevance.
Are there any governments with specific Cd limits? Yes, the EU specifies a Cd limit for chocolate products, per kilogram, (not per day as the MADL), making it clearer to calculate. This enables you to test a product, rather than making assumptions on body weight and servings per day. The EU limit is 0.8mg/kg (ppm) of dark chocolate. So, how do the CR bars stack up to the EU limit? See the last column here.
On average, they are 28% of the EU regulated limit when applying that limit to these serving sizes. Thus, aside from the question of bioavailability (will the Cd even be absorbed?), it looks like these chocolates are all well within the EU limit for Cd content.
How do the bars stack up to common vegetables?
If you appreciate the concept of bioavailability, and the evidence that it is low for Cd and Pb, you could stop reading now. If you still consider it important to care about Cd content in food, you may become wary of your vegetable intake. Even though some of these %s look alarming compared to what is found in the CR chocolate bars, remember what is also important that media often ignore is absolute (vs. relative) value. We are still looking at tiny amounts (<1 ppm) in these foods, and then remember to ask: what % of that <1ppm is bioavailable? Personally, I am not giving up on the benefits of broccoli based on this.
Another interesting graph to consider is this review of the largest food sources of Cd intake:
The top food groups contributing to Cd intake in the US population were cereals and bread (34%), leafy vegetables (20%), potatoes (11%), legumes and nuts (7%), stem/root vegetables (6%), and fruits (5%). (Figure 1)
Figure 1. Cd contribution (µg/day/person) from major food groups among the US population aged ≥2 years in NHANES 2007–2012.
What about Lead (Pb)?
As you now correctly assume, the %s that CR uses for Pb in these products is also based on Prop65, not a government regulated limit, and it is 0.5µg/day. While the original determination analysis appears not to be available, the “No Significant Risk Level (NSRL)” document concludes that for various lead compounds, the NSRL is “23µg /day for Pb Acetate, 41µg/day for Pb Subacetate and 58µg /day for Pb Phosphate”. The Pre-Regulatory Discussion document (August, 2015) states that the ‘default’ method is used: dividing animal research data levels by “10”, and then again by “1,000”. I am going to keep this section shorter because a) the oral bioavailability of lead is extremely low, and b) most foods have extremely low amounts.
Based on CR’s numbers, this is how the bars stack up vs. the EU limit for lead in plant foods – see the column on the right.
Points to Note:
- Bioavailability matters: how much of which food components do you in fact absorb? Does the food (e.g. chocolate) contain iron that helps to further prevent Cd absorption?
- Metals are naturally occurring in volcanic soil. Meanwhile, there are also more metals found globally in soil due to pollution and some pesticides. Exposure sources include air, water, industrial products, paint and certain working environments.
- Foods such as spinach have far higher Cd levels vs. the CR chocolate bars.
- Notwithstanding all the above, chocolate producers should check Certificates of Analyses for each batch of cacao they buy and make sure that Pb is bordering undetectable, and that Cd is <0.5ppm.
- Then, after roasting those beans, producers usually winnow them, removing and discarding the outer shell, where more trace metals may be found. Note: this is not the process for raw chocolate, where they might not discard the shell.
- After mixing with other ingredients to produce final chocolate, any trace metals are further diluted.
- The benefits of cacao polyphenols are copious: from cardiovascular to metabolic to intestinal to skin health. The benefits of leafy greens and broccoli are evident too and in my opinion these many benefits outweigh any traces of Cd ppm that you will most likely hardly absorb.
- Choosing organic certified products means you will go a long way to avoiding unwanted metals that come from pesticides in your food.
Conclusion:
When you see a food news headline and feel shocked and worried, sadly there is a strong probability that it is highly misleading and sometimes even contrary to truth. Ask: “what are these percentages based on?” and “what about bioavailability?” Do not let headlines dictate your diet. If you are considering eating these bars, evaluate them based on their taste, and how much sugar they are adding to your day.
Considerations before pressing ‘publish’: Both scientific publications and media can have harmful effects on people when misleading headlines are published without a few minutes of extra thought (e.g. on bioavailability, on what the numbers are based on). In addition to the time, money and effort wasted on the endeavour, consumers are left feeling afraid, unhappy and confused. Once a seed of doubt is planted, the truth is that very few people go to the trouble to sift through and understand if that doubt is warranted or not. You have thus robbed people permanently of truth that would make their lives happier and healthier. I hope that media outlets try harder to assume proper responsibility for the impact they have and level up their analyses and logic. Also, when one realises that what one published is misleading, should one not consider publishing an apology and explanation?
0.45ppm Limit based on 2018 to 2022 Review and Report for As You Sow
This report looked at the feasibility of reducing Cd content in cacao products. Three out of four experts concluded that for products between 65 and 95%, 0.45ppm Cd should be achievable and for products >95% cacao, 0.96ppm should be the achievable limit. While this 0.45ppm is still half of the EU limit, it does not imply as extreme a low level as the MADL. Unfortunately, this report and discussion ignored the fundamental point of bioavailability for humans eating food.
Despite the low bioavailability of Cd and PB, and my being unconvinced that this is a relevant topic based on the evidence, at NOMOSU, we carry out a variety of testing before and after product formulation and production, including Cd and Pb. Test results for the dark chocolate for Cd are 0.27ppm and for Pb are <0.01ppm. We target <0.4ppm for Cd (lower than the 0.8ppm EU limit) and <0.1ppm for Pb (the EU Pb limit for plant foods is 0.5ppm). This is achieved by careful, delicate sourcing of excellent tasting, sustainably sourced organic cacao and testing each batch.
TLDR: Relevant Criteria to judge your chocolate on:
- The manifold benefits of cacao polyphenols
- Taste
- How much SUGAR is a particular bar adding to your daily sugar intake?
References
Ahn, Timothy et al. (2022), Expert Investigation Related to Cocoa and Chocolate Products: Final Report, March 28, 2022.
Nolan, Shiv et al. (2021), “Bioavailability of arsenic, cadmium, lead and mercury as measured by intestinal permeability.” Scientific reports vol. 11,1 14675. 19 Jul. 2021
CBI.EU, ‘What requirements must cocoa meet to be allowed on the European market?’ Updated 10 July 2024
FDA, ‘FY2018-2020 Total Diet Study (TDS) Elements Report’
EUR-Lex, ‘Commission Regulation (EU) 2023/915 of 25 April 2023 on maximum levels for certain contaminants in food and repealing Regulation (EC) No 1881/2006 (Text with EEA relevance)’, April 2023
Kim, K. et al. (2019), ‘Dietary Cadmium Intake and Sources in the US. Nutrients. 2019; 11(1):2.’
Loria, Kevin, ‘Lead and Cadmium Could Be in Your Dark Chocolate’, Consumer Reports, Updated October 25, 2023
OEHHA, Proposition 65 Maximum Allowable Daily Level (MADL) for Reproductive Toxicity for Cadmium (Oral Route), May 2001
OEHHA, ‘No Significant Risk Levels (NSRLs) for the proposition 65 carcinogens lead and lead compounds (oral)’, June 2002
OEHHA, Pre-Regulatory Draft – for discussion purposes only safe drinking water and toxic enforcement act of 1986 proposition 65 possible amendments to section 25805 Specific Regulatory Levels: chemicals causing reproductive toxicity, august 2015
Zhai, Qixiao et al. (2015), “Dietary strategies for the treatment of cadmium and lead toxicity.” Nutrients vol. 7,1 552-71. 14 Jan. 2015
