The recent news on the supposed finding
that egg yolks are as bad for you as smoking has spread through the media
faster than avian influenza. No doubt
some folks have sworn off egg yolks and modified their egg cracking behaviours,
the egg marketing people are plucking their feathers in disgust and the battle
lines are being drawn for what should be an eggciting debate.
The article prepublished on-line in Atherosclerosis, followed a group of 1262
healthy people attending a prevention clinic in London, Ontario.
The author, a neurologist, has argued repeatedly for the value of
following carotid plaque formation as a risk factor for strokes for which there
is reasonable evidence of a relationship - however showing causation and
definition of the correlation is still open for some debate. The abstract is available and those that can
access the full article are highly recommended to do so. Atherosclerosis
article on egg yolks
The weak study design was based on a single
recall questionnaires of behavior looking at egg eating habits and using this
to define into two groups, those with two or less yolks a week, and those with
3 or more. After carotid plaque
formation was then measured and simple analysis of smoking and egg consumption
adjusting for age and gender against the outcome of plaque size. Most first year students would immediately
flag numerous major design flaws in such an approach. Not bad for a fishing
expedition, but wanting in terms of drawing conclusions.
Of the two groups apparently those with low
egg consumption (n=388) had a mean of
125 ± 129 mm2, and those of the egg eating group (n= 603) 132 ± 142. Oops, somewhere we lost nearly 300 study
participants. Assuming that the written range is
based on a 95% confidence interval around the standard deviation (the most
conservative of the assumptions), the
t-test of these means has a probability of 0.15 – or not significant. Granted, the presented data don’t allow adjustment for age, gender and smoking status
– but the lack of raw statistical significance against the findings when supposedly
only age was adjusted and where the probability is apparently p<.0001 should raise some feathers. (also technically
since the confidence intervals include
zero, it is questionable whether the appropriate statistical approach (ie. using
a Poisson distribution) might have been better).
Are you sensing something rotten in these
eggs?
Noting as well that the absolute difference
between the two groups is only a 6% margin of difference. The conclusion is that this difference is comparable
to that of two-thirds of that of plaque formation for tobacco users. In fairness to the author, they make no
blatant claims that egg consumption is as bad as smoking, in fact they
recommend prospective studies and being sure to adjust for some measure of
weight (which seems to be a critical covariant in this debate). While the full article is not the most eloquent of scientific writing, and critical appraisal gurus will have a hay day de-constructing innumerable problems, the most grievous of transgressions occurred after the publication was printed on-line.
The problem seems to have arisen when the
University of Western Ontario communications folks took a crack at releasing to
the lay media UWO
communications release crowing in the headline that research finds egg yolks
almost as bad as smoking.
Misrepresentation? Possibly.
Certainly a spin on the questionable facts.
The damage is done, just google “egg yolks
as bad as smoking”. Newspapers across
the globe have picked up the coverage of the press release and are running with
the story without the scientific community having any opportunity to pull in
the reins. Like the benefits of oat
bran, vaccines and autism or a hundred other scientific myths – this one has
become entrenched as an urban reality before its time, and the mythbusters will
take years to establish its credibility or not as media retractions are as rare
as hen’s teeth. By then, we will have
genetically modified chickens producing yolkless, or at least cholesterol
reducing yolked eggs and an industry that can propagate the myth for its own
benefit.
Marginal science compounded by the new wave
of high tech communications to support researchers in getting higher scores on
referencing and citing for performance assessments. The question, will this be used to penalize
appropriately both the researcher and the communications people? It would be a progressive day if there was a public statement on how this story was not what it was cracked up to be.
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