The media is reporting an interesting study by a researcher at the University of Miami, Hannah Gardener (I believe based on an abstract presented at a conference - I cannot find a link to the actual study info). It finds that those who drink diet soda daily have a 61% greater risk of having a heart attack or stroke. (and who knows why in remembering this I'm thinking of diet cola? or a particular brand of diet cola?)
Is this surprising? Well as it is currently being reported by the media - that diet soda 'causes' stroke or heart attack - that is stunning! However we really need to have some more information about that study to appropriately digest it and decide whether it has anything to do with causality or disease outcomes.
As I note, I have not seen the actual study - just a couple of media reports (see links below) - so it is impossible to know... but here is what I would consider:
- At what point in life were people studied? Is it young people drinking diet soda and ending up with strokes or older folks?
- When were measures made of diet soda ‘exposure’ vs. when outcomes were identified?
- How does risk in diet soda drinkers compare to risk in drinkers of ‘regular’ soda?
- Who drinks diet soda? What cardiovascular disease (CVD) risk factors do they have already?
- What other things do diet soda drinkers do that could increase their risk? Is there a tendency for those who are overweight or obese to drink it? Is there a tendency for those who drink diet soda to exercise less? What is the overall health of diet soda drinkers as a group? Do we know that obesity and lack of exercise increase risk for heart attack and stroke? (I think we all know the answer to that)
- What other factors associated with greater risk of heart attack and stroke may be common to diet soda drinkers?
- How were these common risk factors managed in the study - were those with early signs of CVD excluded from the study?
- If all other risk factors were controlled for in the study is it still possible to get an erroneous result (yes, because there is probably great similarity between these factors which tends to result in difficulty modeling things statistically)
- Perhaps most important of all: What would be the proposed mechanism of how diet soda 'causes' heart disease or stroke? Is it additives of some sort? Is it caffeine? Is it artificial sweeteners?
From some of the reports I saw, the researcher was careful to say that all this result meant was that further examination of the role of diet soda was needed... I agree with that… but the media has gone way beyond that in some cases…
It's also interesting to think about how you could design a study to prove/disprove this... would we take a healthy group of people and randomize them to drink diet soda daily vs. some other non-diet 'placebo type drink' (i.e. not regular soda I am certain) and see if there is greater risk at the end of the study? How long would we need to wait to see outcomes?
It is tough to actually know and adequately study this question...
Here are the links... http://www.denverpost.com/nationworld/ci_17345702 or
http://www.dbtechno.com/health/2011/02/09/diet-soda-increases-your-chance-of-having-a-heart-attack/
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