The levels of heavy metals found in single servings of some chocolate and cocoa-based products are generally so low that they likely don’t pose a health risk to consumers, according to a new study.

However, research published in the journal Frontiers in Nutrition warns that eating more than one serving per day or eating these products with other sources of heavy metals, such as seafood and uncooked brown rice, may increase exposure levels above recommended limits.

Previous reports from consumer groups and independent testing agencies have highlighted heavy metal contamination in cocoa products such as dark chocolate.

Possible causes include the type of soil where cocoa is grown and industrial processing methods.

Researchers from the George Washington University School of Medicine and ConsumerLab.com analyzed 72 cocoa-containing products. They found that 70 of these products were below the lead contamination limit set by the US Food and Drug Administration (FDA).

However, using the stricter limits set by California’s Proposition 65 law, 31 of 72 products exceeded lead limits, and 13 of 37 exceeded cadmium limits.

Studies show that these products pose no health risk when consumed once in a while, but large amounts may exceed California’s strict limits. The recommended single serving size for chocolate is about 1 to 2 ounces (30 to 60 grams).

The researchers stressed that small or irregular consumption of contaminated products may not be a public health concern, but regular consumption could be problematic.

The National Confectioners Association, which represents the U.S. chocolate industry, responded to the study, saying that “chocolate and cocoa are safe to eat and have been consumed as a gift for centuries.”

The long-term research, conducted over different periods in 2014, 2016, 2019 and 2022, analysed 72 products for heavy metals such as lead, cadmium and arsenic.

The study found that the average concentrations of each metal were lower than California’s conservative Proposition 65 limits.

However, consuming it multiple times daily or combining it with other sources may increase the level of risk.

The researchers advocate for more testing of consumer products to ensure safety, especially given the potential dangers of heavy metal exposure.