Attack of the killer eggyolk
Eating eggs yolks is almost as bad for your heart as smoking, new research suggests.
This one is not really the fault of the newspaper: that is what the researchers suggest, though it is not really what the research suggests.
Researchers analysed lifestyle data from over 1200 men and woman aged about 60 who were attending a vascular prevention clinic in London.
So we’re looking at patients who had been referred to a special clinic because of suspected atherosclerosis, not a representative sample (and that’s London, Ontario, not the better-known one slightly west of the Olympic stadium).
The researchers asked patients about egg consumption and smoking (but did ask for or didn’t use anything else about diet or exercise). They found that patients with a lot of atherosclerotic plaque in their carotid arteries tended to be older, more likely to smoke, and more likely to eat eggs. How much more likely? Well, the ‘almost as bad’ is seriously understating the association they found. If their results are correct, eating one egg yolk has more than ten times the effect on carotid plaque of smoking one cigarette. The estimates don’t look that extreme at first glance, because they count consumption in egg yolks per week, and packs of cigarettes per day.
This is the sort of situation where it’s important to look at what is already known. There is a big US cohort study following up nurses and doctors, which didn’t find any adverse effects of egg consumption. Short-term experimental studies with controlled diets have had mixed results. A few other long-term studies have found heart disease effects specifically in diabetics, but only 11% of the people in this study were diabetics.
It’s possible that eggs increase heart disease risk, especially in diabetics, but the results of this study seem too extreme to be explained by a real risk. Another possibility is that when you ask people about egg consumption, what you get is the number of times per week they consume a good solid traditional breakfast, where eggs are not the only dietary risk factor present.
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »
Why egg yolks, and not egg whites?
12 years ago
The researchers think it’s the cholesterol content.
There’s an ongoing low-level controversy over whether dietary cholesterol matters. I think it’s fair to say that the consensus has been leaning towards “not really”, but there are reasonable people who disagree.
12 years ago