“People who drink three to five coffees a day are less likely to develop clogged arteries that could lead to heart attacks” is a headline that must have sent coffee drinkers’ hearts beating faster in anticipation of future guilt-free consumption.
It follows the publication of a study in the medical journal Heart, which studied a group of more than 25,000 South Korean men and women with an average age of 41, who had no signs of heart disease.
The researchers at the Kangbuk Samsung Hospital in Seoul examined the relationship between levels of coffee consumption and the coronary artery calcium (CAC) score, which is calculated from a CT scan.
They found that people who drank coffee were less likely to have calcium in their coronary arteries than non-drinkers. The lowest levels of arterial calcium occurred in those who drank three or four cups daily.
While the number of study participants is impressively large, the research has some obvious limitations. As an observational study relying on people’s recollection of the number of cups of coffee consumed in the past, it is open to recall bias.
And, while the investigators tried to deal with other potential confounding factors such as smoking, exercise and family history of heart disease, in practice it is impossible to adjust for all confounders in real life.
Both the press releases and reportage of the research left much to be desired. At best, the study found an association between coffee-drinking and lower coronary calcium scores. This is long way from proving causation, a more difficult challenge that would require a randomised forward-looking study.
Then there is the issue of the CAC score itself. This is a parallel marker indicating the possibility of a furred-up coronary artery. However, it is not the gold standard measurement – that is an angiograph which directly visualises each coronary artery and is the ultimate arbiter of the presence of coronary heart disease.
The researchers were cautious in their conclusions.
“Further research is warranted to confirm our findings and establish the biological basis of coffee’s potential preventive effects on coronary artery disease,” they said. They specifically noted they could not recommend drinking coffee in order to prevent cardiac disease.
Contrast this with the PR blurb which announced: “Moderate coffee consumption lessens risk of clogged arteries and heart attacks.” It has all become more than a little confusing. Not long ago, coffee was a confirmed member of the “bad for you club”. Now it is claimed to be so good you should drink up to five cups a day to avoid developing heart disease.
Fat is another dietary factor that has undergone rehabilitation. For decades we were advised to avoid saturated fat to keep our cholesterol in check.
People stopped eating steak and limited their egg and milk intake. The resulting gap was filled with sugar and carbohydrate, which has contributed to a worldwide obesity epidemic.
What is the confused consumer to do? A certain scepticism of mainstream health reportage would help. If possible, try to find out more about the original research – and when it comes to coping with “yo-yo” dietary trends, the sage advice of “everything in moderation” has stood the test of time.