They were probably looking just at poverty. Poor people drink a lot of fizz and are generally unhealthy. So the health outcomes that they found were probably a poverty effect rather than a sweetner effect. They had no data on income so could not control for poverty
The study was "Sugary drink consumption and risk of cancer: results from NutriNet-Santé prospective cohort" by Chazelas et al.
An additional concern about the study is that it was an internet study only -- with all the biases consequent on that. Less sophisticated people would have been much under-represented in the study sample
French researchers tracked more than 104,000 people over ten years, looking at how many sugary or sugar-free soft drinks they consumed.
They found the consumers of both sugary and artificially sweetened drinks are up to 20 per cent more likely to suffer heart disease, stroke or heart attacks than those who avoid soft drinks.
The scientists, at Sorbonne University in Paris, split people into three groups based on their consumption of sweetened beverages.
These categories were labelled as non-consumers, low consumers and high consumers and drinks split into either artificially sweetened or sugary.
A sugar content equalling or exceeding five per cent meant it was considered sugary whereas a sub-five percentage and the presence of 'non-nutritive sweeteners' was enough to be classified as an artificially-sweetened beverage.
The study required participants to fill in three daily diet diaries every six months.
A decade of records from 2009 to 2019 looked for any relationship between intake and heart-related issues, such as stroke, transient ischemic attack (TIA), myocardial infarction, acute coronary syndrome and angioplasty.
A study of more than 5,000 US-based couples found that in 79 per cent of relationships, both people fall into the 'non-ideal' category for heart health. On average, couples also share the same risk factors which can make events such as a stroke or heart attack more likely. This is due to both people falling into an unhealthy routine with poor diet and inadequate levels of exercise.
It revealed people who drank lots of low-sugar diet drinks had the same elevated heart disease risk as those who drank the full-sugar versions.
People who are considered to be high consumers of either artificially sweetened or sugary drinks were 20 per cent as likely to suffer heart problems than people who avoided both types of soft drinks, sticking to other options such as water, tea or coffee.
There was no difference between the two types of drink.
Diet drinks such as Diet Coke, and the artificial sweeteners they contain, are often marketed as a way of reducing calorie and sugar intake.
But experts are concerned at growing evidence that artificial sweeteners alter the body's metabolism, increasing the speed at which sugar is absorbed.
Lead author Eloi Chazelas concluded: 'Higher intakes of sugary drinks and artificially sweetened beverages were associated with a higher risk of cardiovascular diseases, suggesting that artificial sweeteners might not be a healthy substitute for sugary drinks.'
'These data provide additional arguments to fuel the current debate on taxes, labeling, and regulation of sugary drinks and artificially sweetened beverages.'
'To establish a causal link, replication in other large-scale prospective cohorts and mechanistic investigations are needed.'