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You may feel less guilty if you opt for diet sodas over sugary beverages, but drinking them regularly may raise your risk of heart attack and stroke, a study suggests. In a nine-year study of more than 2,500 people, those who drank diet soda daily were 48% more likely to have a heart attack or stroke or die from those events, compared with those who rarely or never drank soda. There was no increased risk of cardiovascular disorders among daily drinkers of regular soda, says study researcher Hannah Gardener, ScD, an epidemiologist at the University of Miami Miller School of Medicine.

The analysis, presented at the American Stroke Association International Stroke Conference (ISC), took into account a host of cardiovascular risk factors including age, sex, smoking, physical activity, alcohol and calorie consumption, metabolic syndrome, and pre-existing heart disease.

Still, the study doesn't prove cause and effect. And even though the researchers tried to account for risk factors that that could skew the results, they couldn't tease out everything, doctors caution.

"You try to control for everything, but you can't," says Steven Greenberg, MD, PhD, vice chair of the ISC meeting committee and professor of neurology at Harvard Medical School.

People who drink a lot of diet soda may share some characteristic that explains the association, he explains.