TAMPA, Fla. (WFLA) — Dark chocolate, that sweet and savory staple for millions across the world, may have a dark side, according to research released by Consumer Reports.

Scientists at the nonprofit advocacy organization recently took a look at 28 popular brands of dark chocolate bars, including products from Dove, Hershey’s, and Traders Joe’s, and found traces of “dangerous heavy metals” in all of them.

Researchers found the dark chocolate bars contained cadmium and lead—two heavy metals linked to a host of health problems in children and adults.

Long-term exposure to even small amounts of heavy metals can lead to a variety of health problems and poses the greatest risk for pregnant people and young children because the metals can cause developmental problems, affect brain development, and lead to lower IQ, according to Tunde Akinleye, the Consumer Report food safety researcher who led the study.

“But there are risks for people of any age,” Akinleye said. “Frequent exposure to lead in adults, for example, can lead to nervous system problems, hypertension, immune system suppression, kidney damage, and reproductive issues.”

For the study, researchers tested a mix of brands, including smaller ones such as Alter Eco and Mast, and more familiar ones, like Dove and Ghirardelli.

For 23 of the bars, eating just one ounce per day would put an adult over a level that public health authorities say may be harmful for at least one of those heavy metals.

While most of the chocolate bars in CR’s tests had concerning levels of lead, cadmium, or both, five of them were relatively low in both.

“That shows it’s possible for companies to make products with lower amounts of heavy metals—and for consumers to find safer products that they enjoy,” Akinleye said.

Consumer Reports used California’s maximum allowable dose level (MADL) for lead (0.5 micrograms) and cadmium (4.1mcg) because there are no federal limits for the amount of lead and cadmium most foods can contain. The organization said it chose California’s dose level because it is the most protective available.

Shown below are the percentages of the MADL supplied in an ounce of each chocolate:

Safer choices

BrandProduct NameLead AmountCadmium Amount
MastOrganic Dark Chocolate
80% Cocoa
14%40%
Taza ChocolateOrganic Deliciously Dark Chocolate
70% Cacao
33%74%
ChirardelliIntense Dark Chocolate
86% Cacao
36%39%
GhirardelliIntense Dark Chocolate Twilight Delight
72% Cacao
61%96%
ValrhonaAbinao Dark Chocolate
85% Cacao
63%73%

High in cadmium

BrandProduct NameLead AmountCadmium Amount
Beyond GoodOrganic Pure Dark Chocolate
70% Cocoa
42%112%
Beyond GoodOrganic Pure Dark Chocolate
80% Cocoa
42%138%
Equal ExchangeOrganic Extra Dark Chocolate
80% Cacao
45%120%
LindtExcellence Dark Chocolate
70% Cocoa
48%116%
Scharffen BergerExtra Dark Chocolate
82% Cacao
49%136%
Alter EcoOrganic Dark Chocolate Classic Blackout
85% Cacao
49%204%
PaschaOrganic Very Dark Dark Chocolate
85% Cacao
68%253%
DovePromises Deeper Dark Chocolate
70% Cacao
74%112%

High in Lead

BrandProduct NameLead AmountCadmium Amount
Tony’sChocolonely Dark Chocolate
70% Cocoa
134%28%
Lily’sExtra Dark Chocolate
70% Cocoa
144%42%
GodivaSignature Dark Chocolate
72% Cacao
146%25%
ChocoloveStrong Dark Chocolate
70% Cocoa
152%60%
LindtExcellence Dark Chocolate
85% Cocoa
166%80%
Endangered SpeciesBold + Silky Dark Chocolate
72% Cocoa
181%31%
Trader Joe’sDark Chocolate
72% Cacao
192%36%
HuOrganic Simple Dark Chocolate
70% Cacao
210%56%
ChocoloveExtreme Dark Chocolate
88% Cocoa
240%83%
Hershey’sSpecial Dark Mildly Sweet Chocolate265%30%

High in both lead and cadmium

BrandProduct NameLead AmountCadmium Amount
TheoOrganic Pure Dark
70% Cocoa
120%142%
Trader Joe’sThe Dark Chocolate Lover’s Chocolate
85% Cacao
127%229%
TheoOrganic Extra Dark Pure Dark Chocolate
85% Cocoa
140%189%
Lily’sExtremely Dark Chocolate
85% Cocoa
143%101%
Green & Black’sOrganic Dark Chocolate
70% Cacao
143%181%

While the report showed some products with relatively high levels of heavy metals, dark chocolate is widely known for its potential health benefits, thanks to studies that suggest its rich supply of antioxidants may improve heart health and other conditions. Dark chocolate also contains a lower level of sugar.