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Chocolate consumption and cardiometabolic disorders: systematic review and meta-analysis

BMJ 2011; 343 doi: https://doi.org/10.1136/bmj.d4488 (Published 29 August 2011) Cite this as: BMJ 2011;343:d4488

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Only the crumbliest flakiest data...

Sir,

As would be expected, the claim that chocolate reduces cardiovascular
events [1] has been warmly received. Any excuse to indulge in one of
life's great pleasures comes as welcome news in these bleak times.

But we should beware those who tell us what we want to believe. And
this is certainly true in the case of Buitrago-Lopez et al. [1] After
scouring the literature, they identified a handful of relevant
epidemiological studies. When we look closely, though, we see that the
meta-analysis was based on data dredged from very large cohort studies.
Unsurprisingly, the results from individual studies were, to say the
least, unimpressive. For example, the German study [2] reported that
chocolate reduced the risk of myocardial infarction by <1% in absolute
terms and the size of the effect was similar in the case of stroke. But
it's the old, old story: trivial treatment effects disguised by the use of
relative risk reductions. [3] And the same applies, of course, to the meta
-analysis. [1]

The authors of the paper duly acknowledged its limitations [1] and so
did the writer of the accompanying editorial, [4] although this prevented
neither from drawing enthusiastic conclusions. And, as has become the
custom in these situations, they also called for randomised trials. But
who is going to fund this research? The pharmaceutical companies have
nothing to gain by doing so. Chocolate manufacturers would be wise to
settle for what they have at present. As for independent research, it is
to be hoped that scarce resources would not be squandered on such flimsy
grounds. But, in any case, the results of large-scale RCTs would not be
available for a decade or more.

In the meantime, the misguided believers in statistics-based research
will peddle the nonsense that the meta-analysis from Buitrago-Lopez et al.
is something of importance. [3] But the claim of a link between chocolate
and the prevention of cardiovascular events is unfounded. Let this be a
warning to the Royal Colleges: it would be premature to begin preparing
mandatory training courses in rock climbing for medical practitioners. The
days when doctors have to scale the side of country mansions to dispense
Milk Tray to their patients are a long way off.

James Penston

e-mail: james.penston@nhs.net

References

1. Buitrago-Lopez A, Sanderson J, Johnson L, Warnakula S, Wood A, et
al. Chocolate consumption and cardiometabolic disorders: systematic review
and meta-analysis. BMJ 2011;343;d4488

2. Buijsse B, Weikert C, Drogan D, Bergmann M, Boeing H. Chocolate
consumption in relation to blood pressure and risk of cardiovascular
disease in German adults. Eur Heart J 2010;31;1616-23.

3. Penston J. Stats.con - How we've been fooled by statistics-based
research in medicine. The London Press. London, November 2010.

4. Mackenbach JP. The temptations of chocolate. BMJ 2011;343;d5883.

Competing interests: No competing interests

07 October 2011
James Penston
Consultant Physician/Gastroenterologist
Scunthorpe General Hospital, Scunthorpe, North Lincolnshire DN15 7BH