Sugar causes dementia?

No wait, artificial sweeteners cause dementia. No, wait…

None of the above?  That’s the my conclusion after looking at the two recent studies that generated headlines like “Is Soda Bad For Your Brain?“.  Both studies came from the same research group looking at the same diet intake data collected as part of the ongoing Framingham Heart Study.  How did the data create two seemingly contradictory results?

Artificial Sweetener Version

Diet recall data was collected from 4000 subjects for three time periods over 10 years.  Keep in mind, this food intake data is based entirely on subjects recalling what they ate and drank.  Can you remember everything you ate and drank even yesterday, let alone months ago?  Is your diet exactly the same all the time, season to season so that a simple recall would accurately reflect what you ate 5 months ago?  Here’s another wrinkle I doubt the researcher considered: when it comes to allegedly healthy behaviors, like choosing diet soda over sugar sweetened drinks, some people are inclined to exaggerate healthy behaviors, so that they’ll look good to the health researchers.  They might actually drink more sugary soft drinks, but they claim to be drinking artificially sweetened low calorie drinks.  So data showing high consumption of artificially sweetened beverages might be wrong.

The subjects were followed for 10 years to assess stroke events and development of dementia.  While there was some increased incidence of both of these for people who claimed to be drinking lots of artificially sweetened soft drinks, when the researchers accounted for existing diseases — diabetes and vascular disease — the increased risk went away.  Which brings up a very important point:  it’s possible that people are drinking more artificially sweetened beverages because they have diabetes.  They’re trying to cut calories, lose weight and cut sugar intake because of diabetes.  And the real risk for stroke and dementia is diabetes and vascular disease, not drinking artificially sweetened soda pop.  The artificial sweetener intake is just a marker for a particular diet and lifestyle associated with diabetes, not a causative factor.

Then there’s one other big problem with this study: there are many different kinds of artificial sweeteners.  They have wildly different molecular structures, are metabolized in very different ways, and are used in very different concentrations.  Assessing the intake of “artificial sweeteners” for a group of people is meaningless.  This fact supports the idea that artificially sweetened beverages — whatever sweetener was used — are markers for a lifestyle, not causes of dementia.

Sugared Soft Drink Version

This is even sketchier.  The food intake data was used to identify people who drank less than 1 sugar sweetened drink per day and compared them to everyone else (more than 1/day, up to.. well whatever).  So the range of possible intake levels was pretty dramatic: 1/2 vs maybe 5?  Or vs 1?  It’s all over the map.

The subjects were assessed for “pre-clinical markers for Alzheimer’s disease and vascular brain injury”.  In other words some changes that can be associated with Alzheimer’s.  But maybe aren’t always.  The higher sugary drink consumers exhibited some of the markers, such as smaller brain volume and poorer results on memory tests.

Hmm, so many possibilities here.  Again the most likely scenario is that people who drink a lot of sugared beverages have other lifestyle and dietary habits that set them up for diseases that involve brain function.  Or it’s possible that they were experiencing these changes as a natural process and the changes made them crave sugar.  That wasn’t considered, but I can imagine a situation where changed brain function affects taste preferences.  Another possibility: the people who claimed to consume fewer than 1 sugared drink/day weren’t always truthful.  See above.  They wanted to present a healthy image to the health researchers and so under-reported consumption of sugared beverages.  In which case the data means nothing.

The final problem

Sugar intake from all other foods was not assessed in either study.  So it’s conceivable that the artificial sweetener drinkers actually consumed lots of sugar from foods, and were making room for that sugar by drinking non-sugared beverages.  You can reward yourself with a couple of doughnuts and a candy bar if you stick to diet soda.  And that would really make a mess of the data.

So do these studies prove anything?  No, except that better studies are needed if anyone is going to accurately assess any role for any artificial sweetener or added sugar in the development of brain diseases.

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