According to a study of more than 2,500 people presented today as a poster at the American Stroke Association International Stroke Conference in Los Angeles, people who drank diet soda daily had a 61 percent increased risk of cardiovascular events compared to those who drank no soda, even when accounting for smoking, physical activity, alcohol consumption and calories consumed per day.
"This study suggests that diet soda is not an optimal substitute for sugar-sweetened beverages, and may be associated with a greater risk of stroke," Hannah Gardener of the University of Miami and her colleagues reported at the conference.
But the questionnaire-based study garnered criticism by experts in diet, nutrition and vascular disease.
"This study has major flaws and should not change anyone's diet soda consumption," said ABC News Chief Health and Medical Editor Dr. Richard Besser.
The researchers used data obtained though the multi-ethnic, population-based Northern Manhattan Study to examine risk factors for stroke, heart attack and other vascular events such as blood clots in the limbs. While 901 participants reported drinking no soda at the start of the study, 163 said they drank one or more diet sodas per day.
"One of the many flaws here is that participants were asked about soda intake at only one point in time, when they entered the study," Besser said. "It is difficult to imagine that people's intake of soda is constant during that period."
Connie Diekman, a registered dietician and director of University Nutrition at Washington University in St Louis, said, "Population-based studies provide some 'food for thought' but shouldn't be used as the basis of nutrition guides for individuals. This study would be another one that indicates more controlled studies are needed."
Drinking regular or diet soda has previously been linked to diabetes and metabolic syndrome, a precursor to diabetes. Surprisingly, Gardener and colleagues failed to detect an increased cardiovascular risk among daily drinkers of regular soda.
"Unfortunately, it may be that individuals with poor dietary habits do resort in some kind of calorie balancing and continue to eat high-calorie sweet foods but reduce their guilt by drinking diet soda," said Dr. Howard Weintraub, clinical director of the New York University Center for the Prevention of Cardiovascular Disease, explaining the propensity to wash down a high-fat meal with low-cal soda.
Although the authors went on to control for metabolic syndrome (a component of which is obesity), peripheral vascular disease and cardiac disease history later in their analysis -- lowering the magnitude of increased risk to 48 percent -- they did not account for variations in eating habits.
"In my 20 years of clinical practice, patients who consume diet soda tend to have more of a sweet tooth; to get more sweet cravings; to eat more foods with added sugar; and to like and eat more processed food than patients who avoid both regular and diet soda," said Dr. David Katz, director of Yale University's Prevention Research Center.