Sunday, January 29, 2023

Heavy Metals in Chocolate

 Chocolate is one of my favourite foods, and may even have health benefits.  But of course, we have to be wary of bias about health claims that we would really, really love to be true!  

 A few studies suggest possible positive mood effects from chocolate consumption, but this research looks a little bit preliminary or questionable (Shin et al).   

Other studies suggest that dark chocolate could help reduce blood pressure (see Amoah et al for a meta-analysis).  

But a recent simple RCT showed that 8 weeks of dark chocolate intake (100 mg per day) did not affect cognition (Suominen et al). 

In any case, I think chocolate, like other delicious foods, has a role in a healthy, happy lifestyle, provided of course that we stick to moderation, and that we choose products which are high quality and lower in sugar.  

The big issue in the past few weeks has been concern that chocolate contains high levels of lead and cadmium.  This was alarming to read about.  The December 2022 Consumer Reports article on this showed that many brands of dark chocolate (including my own personal favourite) contain up to  7 micrograms of cadmium and 1 microgram of lead in a typical 1-ounce serving.    They compare these numbers to California's maximum allowable dose levels, which are 4 micrograms of cadmium per day, and 0.5 micrograms of lead.    

But whenever we see a report like this, it would be important always to find out what the baseline levels are in the population, otherwise we may be much more alarmed than we need to be.  Various studies have looked at average lead and cadmium intake in the diet.   In summary, average cadmium intake in the diet ranges from 5 micrograms per day in the U.S.,  to 10-15 micrograms per day in Europe, to 30 micrograms per day in Asia, from sources such as grains, nuts, vegetables, and shellfish.  Average lead intake ranges from 2-5 micrograms per day in the U.S., to 10-30 micrograms per day in Europe and other parts of the world, from sources such as cereals, meat, and fish.  Recommendations from various sources, such as the FDA, conclude a conservative safe limit of about 58 micrograms a day for cadmium and 12.5 micrograms a day for lead, for a typical 70 kg adult, which are numbers much lower than previous recommendations. 

So the 7 micrograms of cadmium and 1 microgram of lead in a serving of chocolate is still way below most recommended safe limits, and in a ballpark comparable to existing average dietary intakes across the world.  

Of course, any amount of lead and cadmium should be reduced or eliminated in the diet.  And I hope that chocolate makers will take steps to bring down these levels.  But in the meantime, moderate daily chocolate intake is very unlikely to push your lead or cadmium levels up very much higher than they would have been otherwise; the enjoyment and possible health benefits very likely exceed the small risks.  

It will continue to be a longer-term global issue to minimize heavy metal contamination and other contaminants in food and water.  While some of this contamination is "natural," other examples are made worse by industrial pollution.  In any case, there is more work to be done to improve food safety in the coming decades.  


Suominen, M. H., Laaksonen, M. M. L., Salmenius-Suominen, H., Kautiainen, H., Hongisto, S.-M., Tuukkanen, K., Jyväkorpi, S. K., & Pitkälä, K. H. (2020). The short-term effect of dark chocolate flavanols on cognition in older adults: A randomized controlled trial (FlaSeCo). Experimental Gerontology, 136, 110933.

Amoah, I., Lim, J. J., Osei, E. O., Arthur, M., Tawiah, P., Oduro, I. N., Aduama-Larbi, M. S., Lowor, S. T., & Rush, E. (2022). Effect of Cocoa Beverage and Dark Chocolate Consumption on Blood Pressure in Those with Normal and Elevated Blood Pressure: A Systematic Review and Meta-Analysis. Foods, 11(13), Article 13.

Shin, J.-H., Kim, C.-S., Cha, L., Kim, S., Lee, S., Chae, S., Chun, W. Y., & Shin, D.-M. (2022). Consumption of 85% cocoa dark chocolate improves mood in association with gut microbial changes in healthy adults: A randomized controlled trial. The Journal of Nutritional Biochemistry, 99, 108854.

Lead and Cadmium Could Be in Your Dark Chocolate. (2022, December 15). Consumer Reports.

Cadmium and Lead Exposure. (n.d.). Retrieved January 29, 2023, from

Koch, W., Czop, M., Iłowiecka, K., Nawrocka, A., & Wiącek, D. (2022). Dietary Intake of Toxic Heavy Metals with Major Groups of Food Products—Results of Analytical Determinations. Nutrients, 14(8), 1626.

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