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.
The study is not a one-off. Over the past year, other research in the United States 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 could it be that people who drink lots of Diet Snapple or Sprite Zero lead a more unhealthy lifestyle to begin with?
A number of nutritionists, epidemiologists and behavioral scientists think the latter may be true. (It's a theory that will be instantly recognisable to anyone who has guiltily ordered a Diet Coke to accompany their Double Whopper with cheese.)
"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 T.H. Chan School of Public Health and the lead author of a study in April that found that 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 really 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 with overweight or obesity, 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."
Concerns about artificial sweeteners have been around since the 1970s, when studies found that large quantities of saccharin caused cancer in lab rats. The Food and Drug Administration issued a temporary ban on the sweetener, and Congress ordered up additional studies and a warning label, but subsequent research found the chemical to be safe for human consumption. More recently created chemical sweeteners like aspartame and sucralose have also been extensively studied, with little evidence that they negatively impact human health, according to the FDA.
Some studies have even found a correlation between artificial sweeteners and weight loss, but others have suggested they may increase cravings for sugary foods.
"There's no evidence they are harmful to people with a healthy diet who are trying to live a healthy lifestyle," said Dr. Barry M. Popkin, a nutritionist at the University of North Carolina, Chapel Hill. He and others remain concerned that giving diet beverages to young children might encourage a sweet tooth.
Still, many scientists say more research is needed to determine the long-term effects of consuming artificial sweeteners. Although 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.
For consumers, the mixed messaging can be confusing. Dr. Jim Krieger, the founding executive director of Healthy Food America, an advocacy group that presses municipalities to enact soda taxes and increase consumer access to fruits and vegetables, said the new study and others like it raise more questions than they answer.
"Gosh, at this point, you probably want to go with water, tea or unsweetened coffee and not take a chance on beverages we don't know much about," he said. "Certainly, you don't want to drink sugary beverages because we know that these aren't good for you."
Written by: Andrew Jacobs
© 2019 THE NEW YORK TIMES
