Does eating chocolate make you a serial killer?

You may have seen the news item on the BBC website and several other news outlets that suggested that eating chocolate may make you more intelligent!  This originates from a paper by Franz Messerli that was published in the New England Journal of Medicine [1]. He obtained data from several countries on the number of Nobel laureates per-capita and plotted these data in relation to the annual per-capita chocolate consumption.  Why, you ask?  Well, there is limited evidence that dietary flavonoids improve cognitive function and a subgroup of flavonoids known as flavanols are widely present in cocoa, green tea, red wine, and some fruits.

There was a significant linear correlation (r=0.791, P<0.0001) between chocolate consumption and the number of Nobel laureates. The good doctor says, “Switzerland was the top performer in terms of both the number of Nobel laureates and chocolate consumption. The slope of the regression line allows us to estimate that it would take about 0.4 kg of chocolate per-capita per year to increase the number of Nobel laureates in a given country by 1”.  His conclusion was that, “Chocolate consumption enhances cognitive function, which is a sine qua non for winning the Nobel Prize, and it closely correlates with the number of Nobel laureates in each country. It remains to be determined whether the consumption of chocolate is the underlying mechanism for the observed association with improved cognitive function”.

Now call me a skeptic if you like but I just don’t believe this is true.  So I was really pleased that after just a little searching I came across a blog article by James Winters and Seán Roberts, entitled “Chocolate Consumption, Traffic Accidents and Serial Killers”.  They reproduced Messerli’s findings but also showed that chocolate consumption per-capita is significantly correlated with the (log-transformed) number of serial and rampage killers per-capita (r = 0.52, p=0.02). Are we to infer that all this chocolate consumption in Switzerland,  Germany and the UK is causing some people to loose the plot? Maybe not.

More importantly, Winters and Roberts showed that when they controlled for per-capita GDP and mean air temperature, chocolate consumption was not a significant predictor of the number of Nobel laureates. Countries with higher GDP and lower mean outside air temperatures tended to have higher numbers of  Nobel laureates per capita.  So a better explanation for these observations might be that Nobel laureates tend to work in affluent northern hemisphere countries that can afford to support research and where the population buys lots of chocolate.

Reference

1.  Franz H. Messerli FH. (2012) Chocolate Consumption, Cognitive Function, and Nobel Laureates  N Engl J Med; 367:1562-1564October 18, 2012DOI: 10.1056/NEJMon1211064