The temptations of chocolateBMJ 2011; 343 doi: https://doi.org/10.1136/bmj.d5883 (Published 20 September 2011) Cite this as: BMJ 2011;343:d5883
- Johan P Mackenbach, professor
Epidemiologists only rarely bring good news—most messages about the health risks of our preferred consumption and behaviour patterns are unwelcome. It is therefore good to see a positive report on the health effects of chocolate, which people all over the world enjoy, in the linked study by Buitrago-Lopez and colleagues (doi:10.1136/bmj.d4488).1
The authors performed a systematic review and meta-analysis to assess the association of chocolate consumption with the risk of developing cardiometabolic disorders. The authors found no randomised trials, six cohort studies, and one cross sectional study. There was heterogeneity in terms of the measurement of chocolate consumption, methods, and outcomes evaluated. The highest levels of chocolate consumption were associated with a 37% reduction in cardiovascular disease (five studies: relative risk 0.63, 95% confidence interval 0.44 to 0.90) and a 29% reduction in stroke compared with lowest levels.
Chocolate consumption has a long and intriguing history. When the Spanish colonised America they found that the Aztecs used a psychoactive chocolate brew called “xocolātl” (“bitter drink”) in their rituals. The Spanish did not like it, but after sugar was added to a drink made of ground and fermented cocoa beans, it became popular throughout Europe during the 17th and 18th centuries. The development of industrial production processes in the 19th century allowed the incorporation of cocoa into solid tablets and candies, which are the preferred means of consumption today.2
The potential health benefits of consuming chocolate have only recently been discovered. It was initially observed that indigenous Kuna Indians, living on isolated islands off the coast of Panama, had no age related increase in blood pressure or hypertension, unlike their acculturated tribe members on the mainland. Surveys showed that island dwelling Kuna adhered to a diet rich in chocolate, whereas city dwelling Kuna had lost this old habit.3
This stimulated research into the possible health effects of chocolate consumption and the specific compounds responsible for these effects. Laboratory studies and observational and small scale experimental studies on humans have found that chocolate consumption not only lowers blood pressure,4 but that it may also have positive effects on serum cholesterol, platelet activity, endothelial function, and glucose tolerance.5 6
The chemical compounds responsible for these effects are likely to be flavonoids—naturally occurring plant pigments that are common in fruit, tea, red wine, and cocoa beans. The biological mechanisms of flavonoids are still unknown. They have been related to, among other things, their antioxidant properties and to the fact that they increase the bioavailability of nitric oxide, which has vasodilatory and other beneficial effects on the cardiovascular system, but no scientific consensus exists.6 7 8
Studies that link chocolate consumption with health outcomes (instead of intermediate outcomes like blood pressure) are less common, and reasonably good studies are all observational, as shown by Buitrago-Lopez and colleagues’ review.1 Their conclusion that a high level of chocolate consumption may reduce the risk of “cardiometabolic disorders” (cardiovascular disease plus diabetes and metabolic syndrome) by a third is remarkable. If this represents a causal effect it is substantial and comparable in magnitude to that of several other lifestyle related determinants of cardiovascular disease, such as serum lipids.9 10
As the authors note, the underlying studies do not allow a reliable assessment of the dose of chocolate (or its biologically active ingredients) needed to obtain a significant health effect. The observational nature of these studies also precludes a definitive conclusion about the causal nature of the association—as in all epidemiological studies of diet and health, residual confounding by other dietary factors than the one under study or by other aspects of a participant’s lifestyle is always possible.11
Although it is tempting to jump to conclusions with practical relevance, it is therefore too early to make health claims on chocolate products, or for inclusion of chocolate consumption in dietary guidelines for the general public or dietary advice to patients with cardiovascular disease.
A few well designed randomised controlled trials are now needed: adequately powered, with cardiovascular health outcomes, measured over a sufficiently long follow-up period, and looking at the effect of a realistic level of chocolate consumption (with the added energy intake balanced against a reduction in energy intake in other parts of the diet). For epidemiologists and the chocolate industry alike, this must be a temptation no one can resist.
Cite this as: BMJ 2011;343:d5883
Competing interests: The author has completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declares: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.
Provenance and peer review: Commissioned; not externally peer reviewed.