Better Living Through Chocolate?

Of all the food and drink we take the most pleasure in imbibing, red wine and chocolate seem to gather the most scientific (and indeed pseudoscientific) attention with regards to supposed health benefits.  A number of chemicals common to both, for example the antioxidant flavonoids, have been lauded as offering anti-cancer, anti-aging, anti-heart disease and antibacterial properties, and our desire to justify our dietary excesses means that any new studies are certain to provoke media interest.  The latest research from the University of Aberdeen has generated a series of stories claiming that eating chocolate adds years to your life, so should we really be reaching for the Kit Kats to prolong our existence?

The Study

Led by Professor Phyo Kyaw Myint at the University of Aberdeen, the researchers examined the EPIC-Norfolk study, which examines the impact of diet on the health of 21,000 participants over 12 years, and found that consumption of 8-100 g of chocolate per day was associated with an 11% lower occurrence of cardiovascular disease and 25% lower risk of death associated with these diseases.  A 9% lower risk of coronary heart disease, and a 23% lower risk of stroke were also associated with high chocolate consumption.  Extending the examination to a meta-analysis of five further studies also showed a lower risk of cardiovascular disease and death with chocolate consumption. It was also found that the type of chocolate had no effect on the results, with milk chocolate being more popular than dark chocolate (supposedly a better source of flavonoids), and that chocolate consumption was highest amongst younger, thinner adults.

The Reporting

Predictably, the media feasted upon the press release like a hungry academic on free seminar biscuits, generating headlines based around the high levels of chocolate consumption. “A chocolate a day: how just two bars daily can add years to your life” said the Daily Express, “Two chocolate bars a day ‘reduce risks of heart disease and stroke’” said a more sedate Independent, similar to the BBC’s “Eating chocolate linked to ‘lower heart disease and stroke risk’“, and the Guardian led with “More evidence that chocolate may be good for the heart, say researchers“.  The reporting was relatively accurate in this case, reflecting the press release from the researchers and with comments from the lead scientist and other experts warning of the high fat and sugar content of chocolate, although no links to the actual paper, published in Heart, were given.  The headline in the Daily Express about longer life is somewhat misleading, but the paper has a track record in hoping to prolong the existence of its readers (readers – search “daily express live longer” to find articles on the life extending properties of low-fat / vegetarian / high-fat / low consumption / quinoa / wholegrain diets).

None, however, reported the caveat from the press release that reverse causation may explain the results – those with a higher risk of heart disease and stroke may cut chocolate out of their diet in an attempt to avoid these conditions, skewing the results.  This observation is supported by the fact that the highest chocolate consumption was recorded in those deemed to be at the lowest risk of cardiovascular disease.

The Conclusions?

As the authors state, this study is purely observational, so “no definitive conclusions about cause and effect can be drawn“.  Both the authors and the associated experts in the media reports warn against increasing chocolate consumption; surely sensible advice given that 100 g of chocolate contains approximately 500 calories, 50 g of sugar and 20 g of saturated fat (100% of the recommended daily intake for an adult).  It may be, however, that cutting out chocolate from our diets entirely is unnecessary in attempts to avoid these types of disease.  Perhaps the most sage advice came from the school children participating in our “Rewrite the Headlines” workshop investigating previous claims in this area; “chocolate is good for the heart but only if you eat a wee bit!”. Finally, the work also throws up an interesting example of correlation not equalling causation; those who ate the most chocolate in the studies were found to have lower weight (assessed by BMI), and so the press could equally have gone for an “eating chocolate helps you lose weight” stance, but let’s not open up that particular can of worms again!

Kwok C. H. et al. (2015). Habitual chocolate consumption and risk of cardiovascular disease among healthy men and women. Heart. DOI:10.1136/heartjnl-2014-307050