They were supposed to be the healthy alternative to their sugar-rich siblings. But now lovers of diet colas and other low-calorie drinks have been hit by news that will radically undermine those credentials: a counterintuitive study suggesting a link to stroke and dementia.
The study in the journal Stroke may cause a rethink among those worried about obesity, diabetes or a possible early heart attack from sugar-rich drinks who have been considering making a change. It comes to the alarming conclusion that people polishing off one can a day of artificially sweetened drink are nearly three times as likely to have a stroke or develop dementia.
It’s a shocking conclusion. But the first reason to pause is that the study found no such risk in people who drank standard sugary lemonades and colas.
There is little previous evidence with regard to dementia, which is why the researchers were looking at it, but the link between sugar and stroke is very well known. Too much sugar raises the risk of obesity, diabetes, heart attacks and stroke. It’s altogether a bad thing, which is why the World Health Organisation is telling us all to cut down. So what was going on in this study?
The evidence it analyses is pulled from the well-respected Framingham Heart Study – a cohort of more than 5,000 people in Massachusetts, US, whose diets and lifestyles have been monitored for nearly 50 years, with the main objective of finding out more about heart disease. Along the way, researchers have looked at other health outcomes.
What they are up against is people’s capacity for forgetfulness and lies. This is the case with every study into the food we eat – except for those rare ones, almost impossible to do today, which have in effect imprisoned their subjects and controlled every sip and mouthful they took.Researchers understand this and try to take account of it, but it is difficult.
There are several possible other reasons why an increased stroke risk was associated with diet drinks and not sugary drinks. One is what is called “reverse causality”. People who come to realise that they are ill and have a high risk of a stroke then switch their behaviour by choosing diet drinks long after sugary drinks have helped cause the problem.
When it came to dementia, the link with diet drinks that researchers saw disappeared once they took some elements of the health of the people in the study into account. “When the researchers accounted for other risk factors for Alzheimer’s, such as risk genes, diabetes, heart disease, cholesterol levels and weight, this significant association was lost, suggesting that these drinks are not the whole story,” said Dr Rosa Sancho, head of research at Alzheimer’s Research UK.
The researchers point to it themselves: “We are unable to determine whether artificially sweetened soft drink intake increased the risk of incident dementia through diabetes mellitus or whether people with diabetes mellitus were simply more likely…