Field of Science

Slow down there, diet soda study


Recent news has a lot of women I know clasping their heads in horror, guilting over diet soda consumption, or swearing off the sweet, calorie-free little buggers forever.

I'd say to them and to anyone else horrified by the news that diet sodas "cause" "vascular events" to slow down, hoss. Before you trash all those full Coke Zero cans, send them my wa...I mean, note the following:

The study in question has not been peer reviewed. That's right. It was presented at a conference. That does not mean it's invalid or worthless; it just means that what they've said and what they've concluded has yet to undergo the standard processes of scientific evaluation.

So where do we find irresponsible representation of this study? Let's start with the news release from the American Heart Association, at whose conference (correction: release is from AHA; conference is American STROKE association, natch) these data were presented. It begins,
Even if you drink diet soda — instead of the sugar variety — you could still have a much higher risk of vascular events compared to those who don’t drink soda, according to research presented at the American Stroke Association’s International Stroke Conference 2011.
Their findings are summarized as follows:
During an average follow-up of 9.3 years, 559 vascular events occurred (including ischemic and hemorrhagic stroke, which is caused by rupture of a weakened blood vessel). Researchers accounted for participants’ age, sex, race or ethnicity, smoking status, exercise, alcohol consumption and daily caloric intake. And even after researchers also accounted for patients’ metabolic syndrome, peripheral vascular disease and heart disease history, the increased risk persisted at a rate 48 percent higher.
Way down in the news release, after it deals with a second aspect of the team's work (salt), the news release notes the obvious caveats: The researchers did not control for type of diet soda--there are a variety of non-calorie sweeteners and diet sodas out there--and the study relied on self-reported dietary behavior. And while there is mention of controlling for "daily caloric intake," there is not mention of controlling for other relevant dietary factors that might be associated with (a) diet soda consumption or (b) risk for stroke and other vascular events.

I see the absence of peer review as something that requires acknowledgment in any news story covering these findings. I see the above-noted weaknesses also as requiring acknowledgment...preferably early acknowledgment...in any story covering these findings.

Let's see if the news media agree with me.

From MSNBC, "Daily diet soda tied to higher risk for stroke, heart attack." There is no mention of the weaknesses noted above, although some of the quoted experts discuss the potential role of diet in the findings. And there's a strange wandering off task by one researcher who brings up "caramel coloring" as a potential explanation. It seems that it has "been linked to vascular issues." But it also happens to be present in dark-colored sodas, diet or otherwise.

WebMD teases us with, "Is diet soda linked to heart, stroke risk?" Is it? In this piece, an outside expert brings up two other potentially missing variables from the study: family history and weight gain. Good point, outside expert! This piece also notes the caveats already described. Another expert slams the questionnaire the researchers used. And at the end of the piece, after the jump to the second page, WebMD provides this statement:
These findings were presented at a medical conference. They should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.

That's great, but I wish they'd put it as the dek. I wish every report stated that information right up front. Why? Because of reactions like this one from a woman on Twitter:
I learned on the Today Show today that hockey is going to kill Jack & diet soda is going to kill me. (Carbon monoxide & vascular events) FML

And this one, from a woman interviewed for the MSNBC piece:
“This is pretty scary,” said Denise Gainey, a 49-year-old administrative assistant from Amelia, Va. Worried that she might have inherited a higher risk of heart disease, Gainey wants to be careful. “I guess I’ll just be drinking a lot more water,” she said.
That takes me to my favorite find of all today, the LA Times. And I mean that sincerely. Here's the headline:

Diet soda and heart/stroke risk: a link doesn't prove cause and effect

Damn straight. Then the writer, Rosie Mestel, whom I suspect might be a consumer of diet sodas, goes on:
A study just presented at the American Stroke Assn.’s International Stroke Conference reported a link between the amount of diet soda someone drinks and the risk of having a stroke or heart attack.

Really?

Then she brings up all of the caveats. There is not, however, mention of the lack of peer review.

A headline roundup
  • Can diet soda boost your stroke risk? Researchers find a 61% increased risk among those who drink daily (US News and World Report). I note that the much ballyhooed 61% drops to 48% with controlling for factors like metabolic syndrome. There is no mention of the caveats or the lack of peer review.
  • Study: Diet soda drinkers at increased risk for stroke (Fox News). I am completely grossed out by the fact that if you hover over "school of medicine"in the piece (if you get that linked; it changes with each reload), you get an ad for a plastic surgeon. Eww. Anyway, the link is to a limited report highlighting only the screaming numbers with no context.
  • Diet soda: Fewer calories, greater stroke risk (From an ABC affiliate running the ABC version of the piece). I don't think they meant the headline to imply that the absence of calories in diet soda causes a greater stroke risk, do you? That said, early on the piece reads, "This study has major flaws and should not change anyone's diet soda consumption," said ABC News Chief Health and Medical Editor Dr. Richard Besser."
  • Study: Diet soda may increase the risk of stroke (From AOL Health). They blow the lede in this one, referring to keeping weight down. The study didn't control for that. Oops.
  • Diet soda tied to stroke risk but reasons unclear (Seattle Times). The piece starts with, "It's far from definitive proof." At least. My favorite from this piece is, "A simple solution, health experts say, is to drink water instead."
Sure, I'd do that. If it gave me that bit o' sweetness, carbonation, and caffeine that I'm getting from my diet soda.


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