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Chocolate is high in copper but for some reason it does not seem to be a good food for hypers which the high copper content would suggest. Because of this and other reasons, I developed a suspicion that chocolate is high in cadmium.  Searching for medical studies on cadmium and chocolate led me to only two studies.  The first study below is very suggestive that my suspicion is correct and that cocoa beans may be high in both cadmium and lead. The second study confirms that chocolate is high in cadmium (and also nickel). It's possible that the cadmium is introduced to the cocoa during processing, possibly by contact with galvanized containers, and is not natural to the food.
Nahrung 1987;31(5-6):635-6

Lead and cadmium content in cocoa beans (short communication).

Prugarova A, Kovac M

Food Research Institute, Bratislava, Czechoslovakia.

The choice of cocoa beans as the experimental and sample material for study of the contamination with lead and cadmium was inspired by high Pb and Cd limits in foods made on its basis (cocoa powder, chocolate) as well as by the relatively high proportion of these foods in human nutrition. For Cd, the limits in food products are within the range of 0.01 mg X kg-1 (milk) to 1.0 mg X kg-1 (kidneys) whereas the limits for lead range between 0.1 mg X kg-1 (e.g. milk) and 10.0 mg X kg-1 (e.g. tea, yeast, crustaceans, molluscs). Limits for Pb and Cd in foods made on cocoa bean basis are given in Table 1.
Food Addit Contam 1994 May-Jun;11(3):351-63

Beverages as a source of toxic trace element intake.

Pedersen GA, Mortensen GK, Larsen EH

National Food Agency of Denmark, Central Laboratory, Soborg.

Beverages of different kinds have been investigated for their content of lead, cadmium, nickel, chromium, arsenic and mercury. About a ten times higher lead concentration was found in wine than in most other beverages. Cocoa was high in cadmium and nickel and some vegetable juices contained high levels of nickel. The daily intake of trace elements from beverages was estimated. Wine was still the most significant source of lead even if the bottles did not have lead capsules. By consumption of half a bottle per day the daily intake of lead would be doubled and it would contribute 12% of Provisional Tolerable Weekly Intake. Cocoa is an important source of cadmium and nickel, and consumption of tea as well as vegetable juices could increase the nickel intake significantly. The data are compared to Danish maximum limits on lead and cadmium.

Title: Chocolate craving and liking. 

Author(s): Rozin P Levine E Stoess C 

Journal: Appetite. 1991 Dec; 17(3): 199-212 1991 0195-6663 

Abstract: Liking and craving for chocolate and related substances were surveyed in a sample of University of Pennsylvania undergraduates (n = 249) and their parents (n = 319). Chocolate was highly liked in all groups, with a stronger liking by females. Chocolate is the most craved food among females, and is craved by almost half of the female sample (in both age groups). Although this craving is related to a sweet craving, it cannot be accounted for as a craving for sweets. About half of the female cravers show a very well defined craving peak for chocolate in the perimenstrual period, beginning from a few days before the onset of menses and extending into the first few days of menses. There is not a significant relation in chocolate craving or liking between parents and their children. The current motivation for chocolate preference seems to be primarily, if not entirely, sensory. Liking for chocolate correlates significantly with liking for sweets and white chocolate. The liking for the sensory properties could originate in innate or acquired liking based on the sweetness, texture and aroma of chocolate, or it could be based in part on interactions between the postingestional effects of chocolate and a person's state (e.g., mood, hormone levels). Based on correlational data, we find little evidence for a relation between addiction to chocolate or the pharmacological (e.g., xanthine-based) effects of chocolate and the liking for chocolate.