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Effects of theobromine should be considered in future studies

Michigan State University
Department of Food Science and Human Nutrition
GM Trout Building
East Lansing, MI 48824
E-mail: kellycal{at}msu.edu

Dear Sir:

The report by Grassi et al (1) showing that "short-term administration of dark chocolate is followed by a significant increase in insulin sensitivity and a decrease in blood pressure in healthy persons" discusses flavanols as a potential component responsible for the phenomenon reported (acting through an increase in nitric oxide production and availability). The corresponding editorial in the same issue offers other possible mechanisms involving "oxidant-mediated cell signaling" and "the rennin-angiotensin system" (2). It should be noted that another factor, theobromine, may be partially responsible for the decrease in blood pressure reported.

Theobromine is "present in chocolate in uniquely high quantities" and it is cited that dark chocolate contains 237–519 mg theobromine per 50 g (3). Thus, the subjects studied by Grassi et al may have received 474–1038 mg theobromine in each chocolate bar consumed. Theobromine was once used to treat arteriosclerosis, some peripheral vascular diseases, angina pectoris, and hypertension (3). In one report, 5 of 7 subjects could discriminate the subjective effects of theobromine at doses as low as 100–560 mg (4). It was noted that "published work investigating the effects of theobromine is restricted to relatively few articles" (3). A MEDLINE (National Library of Medicine, Bethesda, MD) search using the keywords theobromine and insulin did not provide any results investigating the effects of theobromine on insulin sensitivity. Considering the high concentrations of theobromine in cocoa and its history of use in the treatment of hypertension, theobromine should be investigated or controlled for in future studies that seek to elucidate the components and mechanisms responsible for the recently reported effects of chocolate consumption in healthy persons.

ACKNOWLEDGMENTS

The author had no personal or financial conflicts of interest.

REFERENCES

1. Grassi D, Lippi C, Necozione S, Desideri G, Ferri C. Short-term administration of dark chocolate is followed by a significant increase in insulin sensitivity and a decrease in blood pressure in healthy persons. Am J Clin Nutr 2005;81:611–4.[Abstract/Free Full Text]
2. Fraga CG. Cocoa, diabetes, and hypertension: should we eat more chocolate? Am J Clin Nutr 2005;81:541–2(editorial).[Free Full Text]
3. Smit HJ, Gaffan EA, Rogers PJ. Methylxanthines are the psycho-pharmacologically active constituents of chocolate. Psychopharmacology (Berl) 2004;176:412–9.[Medline]
4. Mumford GK, Evans SM, Kaminski BJ, et al. Discriminative stimulus and subjective effects of theobromine and caffeine in humans. Psychopharmacology (Berl) 1994;115:1–8.[Medline]

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