Artificially sweetened sodas have been linked to a higher risk of Type 2 diabetes for women than sodas sweetened with ordinary sugar, a French study unveiled on Thursday found.
"Contrary to conventional thinking, the risk of diabetes is higher with 'light' beverages compared with 'regular' sweetened drinks," the National Institute of Health and Medical Research (Inserm) said.
The evidence comes from a wide-scale, long-term study, it said in a press release.
More than 66,000 French women volunteers were quizzed about their dietary habits and their health was then monitored over 14 years from 1993 to 2007.
The women were middle-aged or older when they joined the study—born between 1925 and 1950.
Sugar-sweetened sodas have previously been linked to an increased risk of diabetes, but less is known about their artificially sweetened counterparts—often promoted as a healthier substitute.
Researchers led by Inserm's Francoise Clavel-Chapelon and Guy Fagherazzi dug into the data mine to look at the prevalence of diabetes among women who drank either type of soda, and those who drank only unsweetened fruit juice.
Compared with juice-drinkers, women who drank both types of soda had a higher incidence of diabetes.
The increased risk was about a third for those who drank up to 359 millilitres (12 US ounces) of soda per week, and more than double among those who drank up to 603 ml (20 ounces) per week.
Drinkers of light sodas had an even higher risk of diabetes compared to those who drank regular ones: 15 percent higher for consumption of 500 ml (16.9 ounces) per week, and 59 percent higher for consumption of 1.5 litres (50 ounces) per week, Inserm said.
The study found no increase in diabetes among women who drank only 100-percent fruit juice, compared with non-consumers.
The authors noted that women who drank "light" sodas tended to drink more of it—2.8 glasses a week on average compared to 1.6 glasses among women on "regular" sodas.
The findings are published in the latest issue of the American Journal of Clinical Nutrition.
Its authors admitted the study had limitations.
"Information on beverage consumption was not updated during the follow-up, and dietary habits may have changed over time," the paper said.
"We cannot rule out that factors other than ASB (artificially sweetened beverages)... are responsible for the association with diabetes."
The study took account of the women's age and corpulence, but did not keep close track of their eating habits during the study period.
The authors also pointed out that obese people were more likely than thin ones to drink artificially sweetened drinks in the first place.
Fagherazzi told journalists on Thursday the evidence was not sufficient "to advise people to stop consumption of one or the other type of drink"—urging further trials to prove a causal link.
The paper noted previous research which had showed that aspartame—for long the most used artificial sweetener—has a similar effect on blood glucose and insulin levels as the sucrose used in regular sweeteners.
According to the World Health Organisation, 347 million people worldwide have diabetes, a chronic disease which occurs when the pancreas does not produce enough glucose-controlling insulin, or when the body cannot efficiently use it.
Type 2 diabetes, other than Type 1 which starts in childhood and requires insulin treatment, often results from excess body weight and physical inactivity.
Over time, the disease can damage the heart, blood vessels, eyes, kidneys, and nerves—increasing the risk of heart disease, kidney failure, stroke and blindness.