The deadly truth about diet sodas: Sweetener vs sugar

The JAMA Internal Medicine study followed 450,000 European consumers of soft-drinks over 16 years. Photo / 123RF

Commonly-used artificial sweeteners are an even worse threat to a long life than sugar, a new international study reports Andrew Jacobs.

Does guzzling diet soda lead to an early demise?

There was a collective gasp among Coke Zero and Diet Pepsi drinkers last week after media reports highlighted a new study that found prodigious consumers of artificially sweetened drinks were 26 per cent more likely to die prematurely than those who rarely drank sugar-free beverages.

The study, published in the journal JAMA Internal Medicine, followed 450,000 Europeans over 16 years and tracked mortality among soft-drink consumers of all persuasions — those with a fondness for sugary beverages and those who favoured sugar-free drinks.

Given the well-documented health effects of consuming too much sugar, it was little surprise the authors found that people who drank two or more glasses a day of sugar-sweetened beverages were 8 per cent more likely to die young compared to those who consumed less than one glass a month.

But what grabbed headlines, and prompted widespread angst, was the suggestion that drinking Diet Coke could be even more deadly than drinking Coca-Cola Classic.

"Putting our results in context with other published studies, it would probably be prudent to limit consumption of all soft drinks and replace them with healthier alternatives like water," said Amy Mullee, a nutritionist at University College Dublin and one of 50 researchers who worked on the study, one of the largest of its kind to date.

Over the past year, other research has found a correlation between artificially sweetened beverages and premature death.

The problem, experts say, is that these and other studies have been unable to resolve a key question: does consuming drinks sweetened with aspartame or saccharin harm your health? Or do people who drink lots of Sprite Zero lead a more unhealthy lifestyle to begin with?

A number of nutritionists, epidemiologists and behavioural scientists think the latter may be true.

"It could be that diet soda drinkers eat a lot of bacon or perhaps it's because there are people who rationalise their unhealthy lifestyle by saying, 'Now that I've had a diet soda, I can have those french fries'," said Vasanti S Malik, a researcher at the Harvard TH Chan School of Public Health and the lead author of a study in April that found the link between artificial sweeteners and increased mortality in women was largely inconclusive.

"This is a huge study, with a half-million people in 10 countries, but I don't think it adds to what we already know."

The authors of the JAMA paper tried to account for these risk factors by removing study participants who were smokers or obese, and they tried to improve its accuracy through statistical modelling.

But Dr David Ludwig, an obesity specialist at Boston Children's Hospital, said these so-called observational studies cannot determine cause and effect.

"Maybe artificial sweeteners aren't increasing mortality," he said. "Maybe it's just that people with an increased risk of mortality, like those overweight or [obese] are choosing to drink diet soda but, in the end, this doesn't solve their weight problem and they die prematurely."

Still, scientists say the alternative to observational studies — a clinical trial that randomly assigns participants to a sugary drinks group or a diet soda group — isn't feasible.

"Clinical trials are considered the gold standard in science, but imagine asking thousands of people to stick to such a regimen for decades," said Malik of Harvard. "Many people would drop out, and it would also be prohibitively expensive."

Mullee, one of the authors of the study, cautioned against drawing stark conclusions from their data, she said the deleterious effects of artificial sweeteners can't be ruled out, noting studies that suggest a possible link between aspartame and elevated levels of blood glucose and insulin in humans. "Right now the biological mechanisms are unclear but we're hoping our research will spark further exploration," she said.