Many Chocolate Products Still Pose a Slight Heavy Metals Risk, Say Researchers

Most chocolate products sold in the US are safe to consume, according to a new study. A significant minority of products, however, may pose a heavy metals risk if consumed in high quantities.

After testing 72 different cocoa-containing products, bought between 2014 and 2022, a research team from George Washington University found that 43% exceeded the maximum dose of lead allowed in a food product in California; 35% exceeded the state’s cadmium limit.

Products labeled as “organic” were significantly more likely to demonstrate higher levels of both heavy metals.

The results were published in Frontiers in Nutrition.

A slight metallic flavor

Cocoa crops can absorb heavy metals, particularly cadmium, from surrounding soil. The harvested cocoa beans can then become contaminated with lead and other metals during handling and processing.

Cadmium exposure has been linked with a heightened risk of cancers and kidney, bone and lung diseases. Lead exposure can lead to anemia, hypertension and renal impairment.

To help determine the level of heavy metals in chocolate sold in the US, the researchers bought 72 cocoa-containing products from several online and physical retailers between 2014 and 2022. All products were tested for lead, cadmium and arsenic – metals often present in food contamination cases.

The researchers used California’s Proposition 65 maximum allowable dose levels (introduced in 2023) to act as an uppermost limit for each metal. These limits are 0.5 micrograms per day (μg/day) for lead, 4.1 μg/day for cadmium and 10 μg/day for arsenic. 

The average results for all 72 products exceeded the first two limits; the mean serving for lead was 0.615 μg/day, the mean for cadmium was 4.358 μg/day while the mean for arsenic was 0.931 μg/day – well below the 10 μg/day limit.

In total, however, less than half of tested products exceeded the Prop. 65 limits for lead and cadmium (43% exceeded lead levels, 35% exceeded cadmium levels), which indicates that the high mean results were slightly inflated by a few exceptionally contaminated products.

The more recently purchased cocoa-containing items also tended to have lower levels of heavy metals than the products bought in 2014 – an encouraging finding for US consumers.

Products labelled as “organic”, though, tended to have higher levels of lead and cadmium, on average.  

The paper’s findings appear to roughly concur with the well-publicized results of a 2023 Consumer Report, which concluded that a third of chocolate products tested contained harmful levels of lead and cadmium.

To minimize this kind of contamination and protect consumers, the researchers say cocoa harvesters and chocolate manufacturers both need to adopt better quality control practices.

“To mitigate these issues, it is crucial for cocoa producers to: conduct thorough soil and water testing to identify and avoid highly contaminated sites, implement good agricultural practices to minimize the uptake of heavy metals by cocoa plants, ensure clean and safe processing environments to prevent additional contamination,” Leigh Frame, an associate professor of clinical research at George Washington University and co-author of the paper, told Technology Networks.

“Our study aims to raise awareness about these potential sources of contamination and encourage steps towards reducing heavy metals in cocoa products.”

Reference: Hands JM, Anderson ML, Cooperman T, et al. A multi-year heavy metal analysis of 72 dark chocolate and cocoa products in the USA. Front in Nutri. 2024. doi: 10.3389/fnut.2024.1366231

Leigh Frame was speaking to Leo Bear-McGuinness, Science Writer and Editor at Technology Networks.

About the interviewee:

Leigh Frame is an associate professor of clinical research and leadership at George Washington University and executive director of its Office of Integrative Medicine and Health. She brings nutrition and immunity together through clinical, translational research.