Study does not prove diet soda causes Alzheimer’s dis­ease or stroke

The Hamilton Spectator - - HEALTH - SEEMA YAS­MIN

My fam­ily mem­bers are pan­ick­ing about re­cent head­lines claim­ing that diet so­das cause Alzheimer’s dis­ease. While I would love for them to drink fewer so­das, I have to be hon­est: The head­lines were mis­lead­ing, and the new study they re­fer to has ma­jor caveats.

The study did not prove that ar­ti­fi­cial sweet­en­ers cause stroke, Alzheimer’s dis­ease or any type of de­men­tia. In fact, this kind of study de­sign can­not prove cau­sa­tion. To be fair, the au­thors were care­ful to say that the study was not “able to prove cause and ef­fect and only shows a trend among one group of peo­ple.”

Many news ar­ti­cles didn’t re­flect this.

The re­searchers stud­ied nearly 2,000 men and women ages 45 and older for stroke and about 1,500 peo­ple over age 60 for de­men­tia. They tracked how much and what kinds of soda the sub­jects were drink­ing and mon­i­tored their health for a decade.

The study de­ter­mined that drink­ing sug­ary bev­er­ages was not as­so­ci­ated with stroke or de­men­tia. But it found that for peo­ple who drank one ar­ti­fi­cially sweet­ened soda a day, the risk of stroke or de­men­tia was nearly three times higher than it was for peo­ple who con­sumed less than one diet soda a week.

It’s im­por­tant to bear in mind that drinkers of sug­ary so­das may have died from other causes such as heart dis­ease and complications of di­a­betes, and that’s why they don’t show up in the re­sults sec­tion as vic­tims of stroke and de­men­tia. This phe­nom­e­non is known as sur­vival bias. Not men­tion­ing it can be mis­lead­ing.

In a dif­fer­ent study by the same re­searchers, peo­ple who drank sug­ary drinks such as so­das and fruit juice were found to have a smaller brain vol­ume, as well as smaller hip­pocampi, the two horse­shoe-shaped parts of the brain that are cru­cial to mem­ory. In that study, peo­ple who drank sug­ary drinks were more likely to have mem­ory prob­lems.

The study pub­lished in the jour­nal Stroke on April 20 in­cluded mostly white Amer­i­cans, mak­ing it tricky to ap­ply the re­sults to peo­ple of colour who have dif­fer­ent ge­netic and so­cial risk fac­tors for stroke and de­men­tia.

The study em­pha­sizes the “rel­a­tive risk” of stroke and de­men­tia in peo­ple who drink diet so­das. One prob­lem with re­port­ing re­sults us­ing the rel­a­tive risk is that it can make the like­li­hood of some­thing hap­pen­ing seem big­ger than it truly is.

A bet­ter mea­sure­ment is “ab­so­lute risk,” which tells your ac­tual risk of de­vel­op­ing a dis­ease. Where the rel­a­tive risk says the risk of de­men­tia and stroke is three times higher in one group, the ab­so­lute risk says the ac­tual like­li­hood of de­vel­op­ing stroke and de­men­tia is quite low: 3 per cent suf­fered a stroke and 5 per cent de­vel­oped de­men­tia.

Pre­vi­ous stud­ies have found that ar­ti­fi­cial sweet­en­ers in­ter­fere with good bac­te­ria in the gut and are linked to weight gain and dis­eases of the veins and ar­ter­ies.

This doesn’t mean that sug­ary so­das are a health­ier op­tion. Di­ets high in sugar are linked to heart dis­ease, obe­sity and di­a­betes, among other con­di­tions.

While this study didn’t prove that sug­ary so­das cause stroke and de­men­tia, the sci­en­tists did say their re­sults call for more re­search on the health ef­fects of ar­ti­fi­cial sweet­en­ers.

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