As in nature there is no perfect food providing all the essential substances for the human biological functions, so an over-consumption of any food can cause its side effects to human health.
Swiss Renaissance physician, botanist, and alchemist Philippe Theophrastus Bombast von Hohenheim—better known as Paracelsus—asserted in his pioneering studies on toxicology that “dosis sola facit venenum”, that is any substance introduced into the human body is potentially harmful in function of the quantity introduced.
Unfortunately, even the much revered and beloved “food of the gods” is not exempt from exceptions. Cacao and its derivatives are undoubtedly a delicious source of human nourishment and sensory satisfaction since the dawn of time. Nevertheless, chocolate and other cacao products are recently causing greater and greater concern among their regular consumers, as they can come out as dietary carriers of a chemical element that can be harmful to human health under chronic exposure: cadmium.
In order to dismiss unjustified scaremongering about cadmium in chocolate or any other food, two aspects need to be taken into account: 1) how cadmium is distributed in nature and along the agri-food chain; 2) what is the average exposure to cadmium through foodstuffs and consumption styles.
The origin of cadmium in the agri-food chain is in the soil
- Cadmium is a non-essential metal that is found as an environmental contaminant both from natural occurrence and from industrial and agricultural sources. Food is the primary source of exposure (accounting for about 90% of the total exposure to cadmium) for the non-smoking general population.
- Cadmium is unique among the trace elements in that it appears to be taken up readily by plants (despite being non-essential for crops). It is mostly present in its divalent cationic (positively-charged ionic) form as Cd2+ in soils, combining readily with negatively-charged ions, such as Cl- (chloride anions) and (SO4)2- (sulfate anions) to form soluble complexes in an acidic environment. This implies that cadmium solubility is directly proportional to low pH, with cadmium being available the most in increasingly acid soils.
- Calcium ions of Ca2+ have the most similar ionic radius to cadmium ions (Cd2+), so calcium mitigation can effectively compete against cadmium in root mineral uptake.
Why cadmium contamination in foodstuffs is so dreaded
- Even if the dietary cadmium absorption in humans is usually low (3-5%), the intrusive mineral is retained in the human kidney and liver with a very long biological half-life, ranging from 10 to 30 years.
- Cadmium is primarily toxic to the kidney, especially to the proximal tubular cells where it accumulates over time in the cortex. Prolonged and/or high exposure may lead to tubular damage and progress to renal impairment with decreased glomerular filtration rate, and eventually to renal failure.
- Cadmium can also cause bone demineralization, because competing with calcium in its absorption in the human body.
Dietary exposure to cadmium in the European population
In 2012, the European Food Safety Agency (EFSA) published a scientific report named “Cadmium dietary exposure in the European population”.
Since a Provisional Tolerable Weekly Intake (PTWI) for cadmium of 7 μg/kg body weight (b.w.) was established by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) back in 1988, in 2010 the same committee reviewed the previous evaluation and established a provisional tolerable monthly intake (PTMI) of 25 μg/kg body weight corresponding to a weekly intake of 5.8 μg/kg body weight.
Meanwhile, in 2009, the Panel on Contaminants in the Food Chain (CONTAM)—a pool of toxicologists from EFSA—was asked by the European Commission to assess the risks to human health related to the presence of cadmium in foodstuffs. To provide an updated assessment of exposure from foodstuffs, about 140,000 data covering the period from 2003 to 2007 on cadmium occurrence in various food commodities were received from 20 Member States and considered by the CONTAM Panel. Conclusions to the scientific opinion were mainly two:
- Often it is not the food with the highest cadmium levels, but foods that are consumed in larger quantities that have the greatest impact on cadmium dietary exposure. Looking at the food categories in more detail, potatoes (13.2%), bread and rolls (11.7%), fine bakery wares (5.1%), chocolate products (4.3%), leafy vegetables (3.9%) and water mollusks (3.2%) contributed the most to cadmium dietary exposure across age groups.
- The mean dietary exposure for adults across EU countries is between 1.9 and 3.0 μg/kg body weight (b.w.) per week, with vegetarians representing the group with the highest dietary exposure (calculated to be up 5.4 μg/kg b.w. per week) in the overall population.
Recommended Tolerable Weekly Intake (TWI) of cadmium
The CONTAM Panel noted that the reported average level of dietary exposure to cadmium in European countries was close to the Provisional Tolerable Weekly Intake of 5.8 μg/kg b.w., as recommended by the JEFCA in 2010. In fact, vulnerable subgroups such as vegetarians, children, smokers, and people living in highly contaminated areas may even exceed the Tolerable Weekly Intake by about two-fold. Although adverse effects on kidney function are unlikely to occur for an individual exposed at this level, the CONTAM Panel concluded that exposure to cadmium at the population level should be reduced and, in their definitive opinion, they recommended a tolerable weekly intake (TWI) of 2.5 μg/kg body weight in order to ensure a high level of protection for all consumers.
Recommended Maximum Levels (MLs) of cadmium in cocoa products
Following the latest recommendations provided by the CONTAM panel on the tolerable weekly intake of cadmium in the human diet, the previous Regulation (EC) No 1881/2006 regarding maximum levels of cadmium in foodstuffs was amended in May 2014 as Commission Regulation (EU) No 488/2014.
New maximum levels for cadmium in foodstuffs were established and, for the first time, cocoa products were included as a category. In fact, chocolate and cocoa powder sold to the final consumer can contain high levels of cadmium and represent a major source of human exposure, since cadmium levels in cocoa products are related to their cocoa content.
Even if no FAO/WHO Codex Alimentarius MLs for cocoa or cocoa products have been set yet, exporting countries could have their trade affected by some food standards in force, like the strict EU Regulation n. 488/2014. For this reason, in March 2017, the Joint FAO/WHO Codex Committee on Contaminants in Foods (JECFA) agreed to initiate new work on MLs for Cd in chocolate and cocoa-derived products and established an Electronic Working Group (EWG) led by Ecuador and co-chaired by Ghana and Brazil to prepare proposals for MLs for comment. The proposals were harmonized with those specified in the EU Regulation in order to protect consumer health and facilitate international trade, and related to the maximum levels (MLs) for finished products ready for consumption, based on total cocoa solids content (%):
The levels took into account the distribution of cadmium content in samples of cocoa liquor and cocoa powder (range and percentage) in different cocoa growing countries. A limitation of this analysis was that samples from a given country were an average result coming from different origins/regions of the same country. It would therefore be premature for the EWG to recommend MLs for cocoa liquors and cocoa powders until adequate information is available, which could be the subject of future recommendations.
Solutions to ameliorate cadmium uptake at the origin are under development
Waiting for further clarification on the recommended maximum levels of cadmium for cocoa-based raw materials from cocoa-producing countries, what are the actual measures to minimize cadmium absorption from soil to plant?
The European Cocoa Association (ECA) provides in his latest “Cocoa And Chocolate Industry Requirements” some useful advice to mitigate cadmium uptake:
- Increase soil pH, for example by liming, to reduce the availability of Cd.
- Only use phosphate fertilizers and/or manure which has been checked to ensure it does not contain high Cd levels.
- In areas where soil levels of Cd are high, remove pruned material and pod husks from the ground since these could contain Cd which will be released into the top layers of the soil when they decay.
- Avoid irrigation with contaminated water.
- Test for macro and micro nutrient deficiencies.
- Increase organic matter content of soil to stabilize nutrients and heavy metal contaminants.
- Avoid post-harvest contamination, particularly by protecting drying/stored beans from dust and traffic fumes.
- Develop and promote utilization of cocoa varieties or rootstocks with low accumulation levels.
Since both cocoa suppliers and chocolate makers are also consumers of chocolate, all of us as consumers have the right to continue to enjoy chocolate (without overdoing) but also the duty to know the traceability of the main ingredient that composes it. Moreover, if there is a reason why the fine cocoa industry is most appreciated, that is precisely for its transparency.