Welcome to Impact Factor, the most cracking medical commentary on the Internet. I'm Perry Wilson.
This week, the great egg pendulum has swung again. Headlines around the world are proclaiming that eggs can kill you.
Today, I am the Eggman as we discuss the centerpiece of the media maelstrom—an impressive study appearing in the Journal of the American Medical Association. In this study, eggs are cast as delicious, tiny capsules of death.
"I will put it really plainly: Studies that use responses to a food-frequency questionnaire to link to some health outcome are not worth the paper they are printed on."
Now, a study from JAMA shows just the opposite. Does it warrant the same curt dismissal? Not quite. This was about as nicely analyzed a nutritional epidemiology study as you can get. But keep your skeptical caps on.
Researchers combined individual patient data from six large US cohort studies. Participants provided a dietary history from a food-frequency questionnaire at baseline. They were then followed for cardiovascular events and deaths from any cause for a median of 17 years.
The topline results?
Individuals who reported eating more eggs at baseline were more likely to have cardiovascular events in the future. They were also more likely to die from any cause.
Now, the egg eaters were a bit different from the non–egg eaters.
For example, compared with individuals who didn't eat eggs, people who ate two or more eggs a day were much younger; were much more likely to be male, black, and a current smoker; and ate twice as many calories per day.
The authors did a nice job adjusting for these and a variety of other factors. But the negative egg effect remained.
Until they adjusted for total cholesterol intake. After accounting for total cholesterol intake, the harm from eggs disappeared. Simply put, it's not the eggs that kill you, it's the cholesterol in the eggs that kills you.
So why are we talking about eggs? If the culprit here is cholesterol, why did the authors frame the study around eggs? I asked senior author Dr Norinna Allen that very question.
Source: Northwestern Medicine
In other words, they focused on eggs because other people have focused on eggs and they wanted to put this whole thing to bed. But was it enough to change Dr Allen's eating habits?
"Yeah, I have definitely cut back on the amount of eggs. I never ate a lot. But the amount of eggs I feed my kids I definitely cut back on."
Should we all cut back?
There's one little bit of information that didn't make sense to me. When the authors adjusted for serum cholesterol level, the effect of egg-eating and dietary cholesterol intake remained.
The conceptual model underpinning this study looks like this:
Step 1: Eggs contain cholesterol, so eating more eggs means you're eating more cholesterol. Step 2: Eating more cholesterol increases your blood cholesterol level. Step 3: That higher cholesterol level leads to cardiovascular disease and death.
The fact that adjustment for cholesterol intake eliminates the egg-death relationship confirms step 1 of this process. But adjusting for serum cholesterol should have the same effect. It didn't.
In other words, it didn't appear that the bad effect of eating cholesterol was mediated by serum cholesterol level. There are two possibilities here. One, there is some as-yet-undefined effect that needs more research.
Two, it isn't really the dietary cholesterol that is the problem. Maybe egg-eating and cholesterol-eating are just markers of some other unhealthy behavior, unrelated to serum cholesterol but associated with death.
If that's the case, the renewed emphasis on eggs as single servings of heart disease may not be warranted at all.
Medscape © 2019 WebMD, LLC
Any views expressed above are the author's own and do not necessarily reflect the views of WebMD or Medscape.
Cite this: Green Eggs and… Death? - Medscape - Mar 19, 2019.