Drinking a can of diet soft drink a day associated with almost three times higher risk, say researchers – but critics warn against causal connection

Consuming a can a day of low- or no-sugar soft drink is associated with a much higher risk of having a stroke or developing dementia, researchers claim.

Their findings have prompted renewed questions about whether drinks flavoured with artificial sweeteners can increase the risk of serious illness, as heavily sugared drinks have already been shown to do.

“Drinking at least one artificially sweetened beverage daily was associated with almost three times the risk of developing stroke or dementia compared to those who drank artificially sweetened beverages less than once a week,” according to the American researchers who carried out a study published in Stroke, the journal of the American Heart Association.

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“After adjustments for age, sex, education (for analysis of dementia), calorific intake, diet quality, physical activity and smoking, higher recent and higher cumulative intake of artificially sweetened soft drinks were associated with an increased risk of ischaemic stroke, all-cause dementia and Alzheimer’s disease dementia,” the co-authors write.

Those consuming at least a can of so-called diet drinks every day were 2.96 times more likely to suffer an ischaemic stroke and 2.89 times more likely to develop Alzheimer’s disease than those who drank them less than once a week, they found.

Ischaemic strokes occur when blood cannot get to the brain because of a blockage, often one caused by a blood clot forming in either an artery leading to the brain or inside a vein in the brain itself. They comprise the large majority of the 152,0000 strokes a year which occur.

Surprisingly, though, the research also contradicted previous studies by finding that sugared drinks did not raise the risk of either serious outcome. It is based on data for more than 4,300 participants in the Framingham Heart Study, a long-term medical research project in the United States.

“To our knowledge, our study is the first to report an association between daily intake of artificially sweetened soft drink and increased risk of both all-cause dementia and dementia because of Alzheimer’s disease,” the co-authors added.

However, they admitted that they could not prove a causal link between intake of diet drinks and development of either medical condition because their study was merely observational and based on details people provided in questionnaires logging their food and drink habits.

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Matthew Pase, a senior fellow in the department of neurology at Boston University’s school of medicine who was one of the co-authors, said that despite no evidence of a causal link, the apparent connection between sweetened drinks and the two conditions “does identify an intriguing trend that will need to be explored in other studies”.

This is not the first time that sweetened drinks have been implicated in the development of serious ill-health. The paper quotes the Northern Manhattan study as having found that “daily consumption of artificially sweetened soft drink was associated with a higher risk of combined vascular events but not stroke”. It also cites the conclusion of the Nurses Health study and Health Professionals follow-up study that “greater consumption of sugar and artificially sweetened soft drinks was each independently associated with a higher risk of incident stroke over 28 years of follow-up for women and 22 years of follow-up for men”.

Sales of diet versions of soft drinks have boomed in recent years as sales of fully sugared ones have declined sharply.

Defra’s Family Food Survey, published last month, found that sales of regular soft drinks fell by 34.6% between 2010 and 2014, while low-calorie drinks purchases increased by 35.8%. Now just 38% of all soft drinks consumed are fully sugared, it said.

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However, experts and health charities warned against reading too much into the findings reported in Stroke.

“This research does not show that artificially sweetened drinks cause dementia. But it does highlight a worrying association that requires further investigation,” said Dr James Pickett, head of research at Alzheimer’s Society.

Naveed Sattar, professor of metabolic medicine at Glasgow University, said: “This is an interesting paper, but I would strongly caution against the conclusion that artificially sweetened drinks may increase the risk of stroke and Alzheimer’s. There is little other strong evidence to support a link between artificially sweetened drinks and adverse health outcomes.”

The results could have been skewed by people who had already become ill before switching to low- or no-sugar drinks, Sattar added.

Dr Mary Hannon-Fletcher, head of health sciences at Ulster University, said: “These data are sound as far as they go. However, it is important to note ‘the associations between recent and higher cumulative intake of artificially sweetened soft drinks and dementia were no longer significant after additional adjustment for vascular risk factors and diabetes mellitus’ – as the editor also pointed out. So are the conclusions sound? Perhaps not.”

Gavin Partington, director general of the British Soft Drinks Association, said: “Despite their claims, the authors of this observational study admit they found no cause and effect and provide no science-based evidence whatsoever to support their theories.

“In fact, based on the evidence, Public Health England is actively encouraging food and drink companies to use low-calorie sweeteners as an alternative to sugar and help people manage their weight.”

However, Tam Fry, a spokesman for the National Obesity Forum, warned consumers not to see low- or no-sugar drinks as healthy. “Don’t be fooled by the use of the word diet. Diet drinks were dreamed up as a description by an industry wanting to lull you into believing that it was a healthy thirst-quencher. Whether you’re thin or fat and thirsty, and not near a good old-fashioned tap, buy yourself bottled water,” Fry said.