A New Zealand health expert says an American study linking diet drinks with stroke is a warning that artificial sweeteners are not risk-free.
Published in the journal Stroke, the longterm study of post-menopausal women found that those who consumed higher amounts of diet drink had a 23 per cent greater risk of having a stroke than those who drank small amounts or none.
The higher users also had a 29 per cent higher risk of coronary heart disease and a 16 per cent higher risk of death.
Higher use was defined as consuming the equivalent of two or more cans of "diet drinks such as Diet Coke or diet fruit drinks" a week. Low use was less than one a month.
The study involved more than 81,000 women in the Women's Health Initiative Observational Study.
The original study is here (ungated), by Yasmin Mossavar-Rahmani (Albert Einstein College of Medicine) and eight other co-authors. There is also an interesting related editorial by the editors of the journal Stroke here (also ungated). The authors of the study used data from over 81,000 post-menopausal women in the U.S. Three years into the study, the women were asked how often they drank artificially-sweetened beverages (ASBs), like Diet Coke or diet juices. The study then followed those women over time to see what happened, and found that the women who said they drank more ASBs were more likely to suffer coronary heart disease, or to die.
The problem here is that this study doesn't show a causal impact of ASBs on heart disease, stroke or mortality. Although it was carefully designed, and the authors controlled for a bunch of factors also known to affect heart disease or mortality risk, like quality of diet, body mass index, etc., the study still only shows a correlation. As the editorial and the New Zealand Herald article note, this correlation might be causal (and is consistent with a causal story), but it might not. It might be a result of reverse causation. Perhaps instead of ASBs causing heart disease or stroke, being at higher risk of heart disease or stroke causes women to be more likely to drink ASBs; maybe in order to lose weight or to reduce their risk of poor health (maybe under doctor's orders). This is supported by the fact that when they look at sub-groups by BMI, the correlation is only statistically significant for obese women, but not for overweight or normal-weighted women.
Also, the sample was limited to post-menopausal women. I'm unsure how representative of the general population that sample is, even if it is large. Besides which, people's dietary behaviours change over time. This study followed women for an average of 11.9 years, and then based the risk models on one self-reported question about ASB use over the three months at the start of that period. Perhaps women who were more likely to drink ASBs were also more likely to drink sugar-sweetened beverages as they got older? Perhaps they were more likely to be yo-yo dieters, which is bad for you.
So, it is far too soon to conclude that ASBs pose an unnecessary risk to health. At the very least, we would need more careful studies that follow a more widely representative sample of people over time. And even better, if they were randomised so that some drank ASBs and others didn't (although it would be pretty difficult to get ethical clearance for that!).
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