Health effects of chocolate

Theobroma cacao, the cacao tree, produces seeds containing flavanols. The seeds were used to make beverages over some 2000 years in Aztec, Olmec, and Maya civilizations in Central and South America.[2] The drinks were ascribed various curative and stimulant properties, unsupported by experimental evidence. In the 19th century, chocolate as a solid was invented, and milk and sugar were added to create milk chocolate, which is high in fat and sugar.

Throughout history, numerous beneficial effects have been attributed to chocolate consumption, although none has been substantiated.[3] Doubtful research, sometimes funded by the chocolate industry, has at times made suggestions of possible health benefits for these products.[4] This is often based on an unwarranted extrapolation of in vitro studies of isolated compounds in cocoa products.

Chocolate contains polyphenols, especially flavan-3-ols (catechins) and smaller amounts of other flavonoids,[5] which are under study for their potential effects in the body.[6] The following table shows the content of polyphenols and theobromine in various preparations of chocolate.

Although research suggests that even low levels of lead in the body may be harmful to children,[8][9] it is unlikely that chocolate consumption in small amounts causes lead poisoning. Some studies have shown that lead may bind to cocoa shells, and contamination may occur during the manufacturing process.[10] One study showed the mean lead level in milk chocolate candy bars was 0.027 µg lead per gram of candy;[10] another study found that some chocolate purchased at U.S. supermarkets contained up to 0.965  µg per gram, close to the international (voluntary) standard limit for lead in cocoa powder or beans, which is 1 µg of lead per gram.[11] In 2006, the U.S. FDA lowered by one-fifth the amount of lead permissible in candy, but compliance is only voluntary.[12] Studies concluded that "children, who are big consumers of chocolates, may be at risk of exceeding the daily limit of lead; whereas one 10 g cube of dark chocolate may contain as much as 20% of the daily lead oral limit. "Moreover chocolate may not be the only source of lead in their nutrition"[13] and "chocolate might be a significant source of cadmium and lead ingestion, particularly for children."[14]

In sufficient amounts, the theobromine found in chocolate is toxic to animals such as cats, dogs, horses, parrots, and small rodents because they are unable to metabolise the chemical effectively.[15] If animals are fed chocolate, the theobromine may remain in the circulation for up to 20 hours, possibly causing epileptic seizures, heart attacks, internal bleeding, and eventually death. Medical treatment performed by a veterinarian involves inducing vomiting within two hours of ingestion and administration of benzodiazepines or barbiturates for seizures, antiarrhythmics for heart arrhythmias, and fluid diuresis.

A typical 20-kilogram (44 lb) dog will normally experience great intestinal distress after eating less than 240 grams (8.5 oz) of dark chocolate, but will not necessarily experience bradycardia or tachycardia unless it eats at least a half a kilogram (1.1 lb) of milk chocolate. Dark chocolate has 2 to 5 times more theobromine and thus is more dangerous to dogs. According to the Merck Veterinary Manual, approximately 1.3 grams of baker's chocolate per kilogram of a dog's body weight (0.02 oz/lb) is sufficient to cause symptoms of toxicity. For example, a typical 25-gram (0.88 oz) baker's chocolate bar would be enough to bring about symptoms in a 20-kilogram (44 lb) dog. In the 20th century, there were reports that mulch made from cacao bean shells is dangerous to dogs and livestock.[16][17]