Diet Soda & Stroke: Not as Sweet as we Thought?

by Tania Houspian, PharmD 2011

Once upon a time, you were told that soft drinks like Coca-Cola or Pepsi were bad for you because they are packed with sugar and empty calories.  Being the intellectual, health-conscious individual that you are, you made the switch to the diet version of your favorite soft drink. The after taste took some getting used to but you stuck with it and gave yourself a pat on the back for the change. Now your favorite news outlet is telling you that a recent poll found that people who drink diet drinks are twice as likely to suffer strokes. Your world has been rocked and you don’t know what to do.  Let’s take a look at what the poll really found and where to go from here.

The poll heard ‘round the Diet Soda World


The poll that everyone is talking about was conducted by researchers at the Columbia University Division of Stroke and Critical Care. The poll was part of the Northern Manhattan Study (NOMAS) investigating “reasons for race-ethnic differences in stroke incidence and confirming findings of the protective, beneficial effects of physical activity and moderate, daily alcohol intake.” Still with us?  Prior to this study, nobody would have ever linked diet drinks with strokes…it’s not a logical connection by any means.  The investigators were simply tracking people’s lifestyles and trying to identify correlations with their risk of stroke.

So how does a poll work?

We have all been called or sent letters from companies asking if you’d like to be included in a poll. If you were nice enough to respond, then you probably answered a series of questions like the following:

  • Poll: Are you satisfied with your cable provider?
  • Participant: Um, yeah. Sure.
  • Poll: How many other cable providers did you research before choosing your current cable provider?
  • Participant: Um, oh, um, I don’t know. Four? No, two?

The NOMAS poll was a food frequency questionnaire. As the name suggests, the questionnaire asked participants how frequently they consumed different kinds of foods. The way the diet soft drink issues arose was with a question on the poll asking responders what quantity and type of soda they drank. Based on their responses the investigators split up participants into 7 groups.

  • Group 1: No Soda (less than one soda of any kind per month)
  • Group 2:  Moderate Regular Soda only (anywhere from one soda a month to 6 per week)
  • Group 3: Daily Regular Soda (at least one per day)
  • Group 4: Moderate Diet Soda only
  • Group 5: Daily Diet Soda only
  • Group 6: Moderate Diet Soda + Any Regular Soda
  • Group 7: Daily Diet + Any Regular Soda

The researchers then followed these patients for an average 9.3 years and saw a trend: the groups who drank diet sodas had a higher incidence of stroke. To better elucidate this connection, they excluded other lifestyle factors that could increase someone’s chance of having a stroke such as age, sex, race, ethnicity, smoking status, exercise, alcohol consumption, daily caloric intake, metabolic syndrome, peripheral vascular disease and heart disease history. Even after making these adjustments, the researchers still saw a 48% higher risk of stroke in diet soda consumers.

How good is the poll’s data?

It’s hard to say what the poll really shows because the data hasn’t been published yet. All the news and media coverage came from a presentation made by the researchers at the American Stroke Association’s International Stroke Conference 2011. Even more unfortunate is that the questionnaire did not ask participants which brands of sodas they were drinking so there is no way to identify specific artificial sweeteners or colorings that could be the underlying cause of this apparent increased risk.

A Grain of Salt

We know what the researchers announced and some of the basics about how they conducted their research but here is your grain of salt: A poll relies heavily on the honesty and accuracy of the person being polled. We don’t know about you, but we can barely remember what we had for breakfast by the time lunch rolls around. What we’re trying to say is that a poll is not hard science. Polls are great to pick up on trends and people’s attitudes. They can also reveal potential relationships between activities and events that will then require solid scientific research to prove.  This is one of those situations.  Even the researchers behind the study clearly state that more research is needed before a conclusive statement can be made. Our extensive literature search did not uncover a single study even hinting at an association between diet drinks and strokes. However, that didn’t stop the media from taking this story and running with it.  Fear sells.

What do we diet drinkers do now?

The take home messages from the study are as follows:

1) Take the media’s interpretation of scientific data with a grain of salt.  It’s hard to say how good or bad the data is until their findings are published and scrutinized by the scientific community.

2) In the meantime, we are 100% behind you if you’d like to start drinking water instead of diet soda. We do know that water is a healthier choice that soda and we support any campaign that increases the odds of drinking more water.

Questions? E-mail the Author: houspian@myhousecallmd.com

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