Are diet drinks linked to heart and stroke risk?

Two people drinking a fizzy drink
19 February 2019
Research has found a link between frequently drinking artificially sweetened drinks and an increased risk of stroke, heart disease and death. We look behind the headlines. 
Women drinking more than two diet drinks a day have an increased risk of stroke, coronary heart disease and death, according to a new study.

The research 

The findings were based on a study of more than 80,000 women, who were participants in the Women’s Health Initiative Observational Study. This is a long-running American study of the health of postmenopausal women aged 50 to 79. The research comes from the Albert Einstein College of Medicine in New York, and participants’ health was monitored for an average of 12 years. 
A 12 fl oz can (355ml – slightly larger than the standard UK can size of 330ml) was used as the measure of one diet drink. Most women in the study (64.1%) said they never consumed diet drinks, such as diet cola, or consumed them less than once a week. Only 5.1% (4,196 people) consumed two or more artificially sweetened drinks a day. These women were more likely to be obese and exercise less, although the study results were adjusted to take account of factors which can affect heart disease and stroke risk.

Women drinking two or more diet drinks a day were found to have a 31% increased risk of ischaemic stroke

Compared to women consuming one or fewer diet drinks a week, women consuming two or more a day were more likely to have a stroke (23% increased risk), coronary heart disease (29% increased risk), and to die (16% increased risk).  
When the analysis was broken down for different types of stroke, women drinking two or more diet drinks a day were found to have a 31% increased risk of ischaemic stroke, the most common type of stroke which is caused by a blood clot blocking an artery in the brain.
The researchers didn’t find any increased risk of haemorrhagic stroke, which is caused by a burst blood vessel in the brain.  This was one of the first studies to assess the risk of different types of stroke in relation to intake of artificially sweetened drinks.  
When the data was analysed further, some of the risk increases were only found in certain sub-groups in the study, so more research would be needed to fully understand whether these findings apply to everyone.  

How good was the research?  

A limitation of the study is that women self-reported their consumption of these drinks, meaning that the data relied on their memory being accurate. Also the study didn’t collect information about what specific types of drinks were being consumed, so the results can’t tell us if particular drinks have stronger or weaker associations with stroke and heart risks.
In particular, the study authors say it wasn’t clear whether participants would have included tea and coffee sweetened with artificial sweeteners in their responses.   

The results can’t tell us if particular drinks have stronger or weaker associations with stroke and heart risks

Most importantly, because this was an observational study - rather than a trial with women being asked to consume different amounts of diet drink – it can only find associations between different factors. It can’t determine whether the drinks were directly responsible for the higher risks of stroke, heart disease and death among women consuming more.  
It’s possible that people who already have a higher risk of stroke and heart disease drink more diet drinks, perhaps as part of an effort to manage their weight. The study authors also said that undiagnosed diabetes in some participants could have influenced the findings.  

The BHF view 

All artificial sweeteners undergo a safety assessment by the European Food Safety Authority (EFSA) before they can be used in food and drinks. This means that the sweeteners approved for use in the UK, such as aspartame, saccharin and stevia, have been found to be safe for human consumption. 
There have been suggestions that artificial sweeteners may have a stimulating effect on appetite, and may have effects on the metabolism resulting in weight gain and obesity, but the evidence around this is inconsistent, and in some cases based on mice rather than humans. More research is needed to understand these potential effects.  
Tracy Parker, Senior Dietitian at the British Heart Foundation, said: 
“We’re all too familiar with the fact that sugary drinks are not only bad for our teeth, but the excess calories can make us put on weight, increasing our risk of suffering a heart attack or stroke. 

To definitively understand the link between diet beverages and disease risk, more research is needed.

Tracy Parker
“Although this study rightly suggests that diet drinks don’t do us any good, it’s observational. This means we don’t know why these drinks might be linked to an increased risk of heart and circulatory disease. To definitively understand the link between diet beverages and disease risk, more research is needed.  
"But that doesn’t mean you’re off the hook! Put your sugary drink down and swap it for a water. Your body will thank you for it.” 

How the research was reported 

The Sun warned, “Diet drinks are NOT harmless”, which didn’t reflect the fact that the scientists only observed an association, not a direct causal link. While the results of the study do raise concerns about the potential impact of diet drinks on our health, an observational study like this isn’t able to prove that diet drinks were the cause of any strokes or heart disease.  
The Daily Mail implied that the study had taken regular measurements of women’s drink intake over the course of the study - “A major study of 80,000 women over 50 tracked their drinking over 12 years”- whereas women were only asked about their diet drink intake once – it was their health that was followed up for 12 years on average. This one-off measurement is a limitation of the study, meaning it wasn’t able to track whether changes in participants’ consumption lead to any changes in their health outcomes.   


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