Is chocolate good for your heart?


Many people can't resist the allure of chocolate, and science is no exception. But do reports of the health benefits of chocolate really stand up to scrutiny? Elizabeth Finkel investigates. 


Four millennia after the Olmecs used the cocoa bean in their rituals, chocolate has lost none of its thrall.

Now science is trying to discover its secrets. But you have to wonder whether science itself has become mired in chocolate. Take the 2012 report from the prestigious New England Journal of Medicine suggesting nations that ate more chocolate produced more Nobel Prize winners.

Author Franz Messerli, a cardiologist from St. Luke’s–Roosevelt Hospital in New York, reported “a close, significant linear correlation” between per capita chocolate consumption and the number of Nobel laureates per 10 million persons in 23 countries.

Switzerland was the top performer in both the number of Nobel Laureates and chocolate consumption. Messerli’s hypothesis? “It seems likely that in a dose-dependent way, chocolate intake provides the abundant fertile ground needed for the sprouting of Nobel Laureates.” Messerli also offered that the winning chocolate ingredient might be flavanols, chemicals shown to improve blood flow to the brain in elderly humans and help ageing rats navigate mazes.

I hope you are guffawing. “The paper was clearly a huge joke, and a fine teaching lesson in spurious correlations,” says David Spiegelhalter, a University of Cambridge statistician who holds the title of Winton Professor for the Public Understanding of Risk. Messerli admitted as much to COSMOS: “The correlation is unreal.”

OK, the findings thrown up by this study are not meant to be taken seriously. But it’s far from clear what to make of other chocolate studies.

Food is a mixture of variable and unknown substances, warns Daniele Piomelli, a pharmacologist at the University of California, Irvine. In 1996, Piomelli went prospecting into the dark matter of chocolate to find clues as to its spell over us. What he found made him an overnight celebrity. Anandamide – its name comes from the Sanskrit word for bliss – is a natural brain chemical with properties similar to THC, the active drug in cannabis. Piomelli found a fatty chemical in chocolate that would raise its level in the brain. “I had queues of chocolate executives lining up outside my lab,” he says. They were anxious about any link to cannabis, and 17 years on Piomelli still gets calls from journalists every Valentine’s Day asking about it.

But the concentration of drug-like molecules released into the bloodstream is very low. “We are talking about something much, much, much less than a high,” says Piomelli. Nevertheless he adds, “chocolate is something more than a food”. Recent findings show that the tongue’s taste receptors are sensitive to compounds such as anandamide. As the chocolate’s fatty chemical lands on your tongue, it could raise the concentration of any locally produced anandamide, which in turn sends a bliss signal direct to the brain. So chocolate ends up tasting especially good. Piomelli says it is still speculative but this may at last explain something of chocolate’s bewitching taste. Overall your body’s message is “eat more of that fatty food”, Piomelli says.

Chocolate companies may be unenthusiastic about research on the links between cannabis and chocolate. But research they adore is that which shows health benefits. According to one estimate some 70% of the research on the health benefits of chocolate is industry-funded.

There have been many studies showing chocolate can improve cognition of mice and men, and even of snails. The suggested mechanism is that chocolate flavanols improve the blood flow to the brain. However, the findings are not that impressive. In a 2010 study by researchers at the Centre for Human Psychopharmacology, Swinburne University of Technology, Melbourne, young males given a drink rich in cocoa flavanols performed better on cognitive tests such as counting backwards by three than peers who got the same drink minus the flavanols. But three years later, a similar experiment in a group of 45-60 year olds at the same lab did not find any cognitive improvement. The subjects did, however, report being in a better mood after 30 days on cocoa. The researchers suggested the effect might be a result of flavanols acting like mild tranquilisers, and tweaking the brain’s GABA-a receptor.

With so much science, what is the message reaching the public?

In 2011, the British Medical Journal reported a startling result. High levels of chocolate consumption (regardless of whether it was dark, light, a drink or cookies) reduced cardiovascular disease risk by a whopping 37% and stroke by 29%. Now before reaching for a chocolate bar, bear in mind this is the same type of “observational” study that linked Nobel prizewinners to chocolate consumption – the one that “was a fine teaching lesson in spurious correlations”. In this study, which was not industry-funded, the researchers combined seven studies of 114,000 people, who were asked to remember the details of their chocolate consumption over the previous eight to 16 years. Even the authors warn, “any conclusion should be treated with caution”.

Stronger data has come from looking at the direct effects of chocolate consumption on the elasticity of blood vessels. The higher the elasticity, the better blood pressure and cardiovascular health is likely to be. For a 2012 paper in the American Journal of Clinical Nutrition, Aedin Cassidy, a professor of nutrition at the University of East Anglia in the UK, reviewed 42 studies, where 1,297 participants showed improved cardiovascular health after a dose of chocolate, cocoa or other source of flavanol. The studies lasted up to 18 weeks, and the subjects had their blood vessel diameters measured. Cassidy is convinced there was a benefit to blood vessel elasticity that translated to lower blood pressure.

Evidence to explain what is happening comes from a study, funded by the Mars company, published in 2006 in the Proceedings of the National Academy of Science. Hagen Schroeter and colleagues showed that epicatechin, one of the chocolate flavanols, triggered the release inside blood vessels of nitric oxide, a gas known to relax the band of muscles that surround the vessels.

With so much science, what is the message reaching the public? In May, 2012, the famously hard-nosed European Food Safety Authority (EFSA) issued a report saying: “Cocoa flavanols help maintain endothelium-dependent vasodilation, which contributes to normal blood flow … In order to obtain the claimed effect, 200 mg of cocoa flavanols should be consumed daily. This amount could be provided by 2.5 g of high-flavanol cocoa powder or 10 g of high-flavanol dark chocolate.” In other words a square or so of dark chocolate.

No doubt the wording was music to the ears of William Callebaut, the chocolate company that had requested EFSA to review the evidence, but for many scientists the statement jarred. “Everyone found it remarkable,” says Cassidy. According to Spiegelhalter: “The problem with EFSA’s analysis is that it looks at a single outcome measure and has no concern with overall effects.”

There seems an obvious big leap here. Do the health benefits for people behaving well in a controlled 18-week trial mean anything for the community at large? Stopping at one square of chocolate is hard, and eating more has clear drawbacks.

If there is a health benefit to chocolate flavanols, and most research identifies epicatechin, it is also readily available in sources such as tea and apples, particularly the skin of the “pink lady” variety, according to pharmacologist Kevin Croft at the University of Western Australia.

Not all public agencies have been seduced. The National Heart Foundation of Australia issued a 2011 bulletin urging people “not to eat chocolate in the belief that it will reduce their risk of heart disease”.

But chocolate clearly has staying power; the siren song of its health benefits is likely to continue to call seductively above the drone of warnings.

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