As a confessed chocaholic, I really wanted to believe the recent headlines claiming that eating chocolate would lower my risk of a heart attack or stroke. Sadly, having read the research paper, I’m left bemused that such a respectable British medical journal, Heart, agreed to accept it for publication.
The first inkling that things might be a bit off was that the data came from a study originally designed to assess cancer risk factors – not heart attack or stroke. Known as the European Prospective Investigation into Cancer (EPIC) trial, it’s one of the largest cohort studies in the world, with more than half a million participants across 10 European countries.
Anyway, the UK arm of the study, EPIC-Norfolk, involved almost 21,000 men and women who were followed for an average of 11 years. When these participants were divided into five groups, based on their habitual chocolate consumption, those eating the most chocolate appeared to have a 23% lower risk of heart attack or stroke over the 11 year study period, than those who ate no chocolate at all. I know. I was shocked, too. How can anyone survive without chocolate?
Why The Results Are Nonsense – Part 1
The assessment of chocolate intake was a strangely haphazard affair. The baseline food-frequency questionnaire included three relevant questions, asking the frequency of consumption of:
- ‘Chocolates singles or squares’ – average portion size 8g each.
- ‘Chocolate snack bars, for example, Mars, Crunchie’ – average chocolate intake 50g.
- ‘Cocoa, hot chocolate (cup)’ – average portion size 12g powder weight.
Average ‘portion size’ was then multiplied by frequency of consumption (never or less than once per month; 1–3 per month; once a week; 2–4 per week; 5–6 per week; once a day; 2–3 per day; 4–5 per day; 6+ per day) to derive each person’s average chocolate intake. The sum of the weights of these foods, rather than their cocoa or flavonoid antioxidant content, was what was used in subsequent calculations.
No information was available about whether the chocolate consumed was white, milk or dark – but as snack bars accounted for the greatest weight, milk chocolate was likely the most prevalent.
Eighty-six people claimed to eat 100g or more chocolate per day (round of applause) but these were excluded on statistical grounds – they were assumed to be confused or having a laugh , despite the fact that a previous BMJ paper had suggested that eating 100g chocolate was the right way to go! The remaining candidates were divided into five groups (known as quintiles) of which the lowest 20% were non-consumers.
Among those classed as consumers, average chocolate intake was relatively low, overall, at just 7g per day – less than one teeny, weeny square. But for the top 20% of consumers, in Quintile 5, intakes ranged from a respectable 98.8 grams down to just 15.6 grams per day! You would have been classed as a ‘top’ consumer by eating just two squares of white chocolate (sugar, cocoa butter, cream) per day (average portion size of 8g means two measly squares weigh 16g).
Stick with me, as it gets even more bizarre.
Having filled in the base-line food frequency questionnaire, participants were followed-up for an average of 11 years. During this time, 11.6% experienced a heart attack, 4% experienced a stroke, and 1.2% experienced both.
The researchers claim that those eating the most chocolate were 11% less likely to have a heart attack or stroke overall than those eating no chocolate (although for the statistically-minded, the confidence interval reached 1.00 which makes this borderline dubious). They also claimed that high consumers were 25% less likely to have a fatal heart attack or stroke than non-consumers.
Why The Results Are Nonsense – Part 2
None of the health journalists crafting their feverish headlines could have read the original paper. If they had, they would have noticed a little statement, slipped into page 3, which admitted that the associations so widely publicised were ‘… attenuated after adjustment for a range of cardiovascular risk factors and after adjustment for a set of dietary parameters.’ In other words, once the researchers accounted for variations in blood pressure, cholesterol levels, diabetes, triglycerides, exercise level, calorie intake and alcohol consumption, the difference between ‘top’ chocolate consumers (which could mean just two squares of white chocolate per day, remember) and non-consumers was reduced to a 9% difference which, because the statistical confidence interval (CI 0.80 – 1.04) crosses the magic level of 1.0, is almost certainly not statistically significant. These findings were down to chance alone.
But let’s assume, for a moment, that the touted headlines were true…
These findings are based on a single questionnaire completed by participants up to 11 years previously. Has your chocolate intake changed over the last decade? Mine certainly has (for the better, I’m pleased to note). And what if the questionnaires were filled in after the Easter bunny paid a visit? Or after Christmas? Or a birthday or anniversary? Just saying…
And according to the methodology used, those eating the most chocolate (around 16g to 99g per day) could have savoured a square of quality dark chocolate (8g per serving) and cradled a large mug of cocoa at bedtime (12g powder per serving) but it was much more likely, based on chocolate weight alone, that they were munching on sugar-laden snack bars (50g per serving).
If we truly accept (despite the dubious statistics) that the ‘top’ consumers of chocolate had a lower risk of heart attack or stroke, then the only possible conclusion is that the strongest protection comes from scarfing down a Crunchie or a Mars bar. Or both.
Of course, it’s also possible that those who were most ill, and most at risk of a heart attack or stroke or cancer, were warned off sweets by their doctors so that only the fit and well were left to take one or two bars of chocolate for the team.
Has the Silly Season arrived early? Plenty of good quality studies show that eating good quality chocolate can lower blood pressure, insulin resistance and the risk of heart attack and stroke. This current study, which gained generous acres of publicity, is not one of them.
Image credits: pixabay