People who think they’re being healthy by drinking diet soda and keeping their weight down could be mistaken.

New research finds that diet may increase the risk of stroke by as much as 61 percent.

“If our results are confirmed with future studies, then it would suggest that diet soda may not be the optimal substitute for sugar-sweetened beverages for protection against vascular outcomes,” said Hannah Gardener, lead author of the new study and epidemiologist at the University of Miami Miller School of Medicine in Miami, in a statement.

The findings were presented today at the American Stroke Association’s International Stroke Conference 2011 in California.

The research was based on 2,564 people who participated in the Northern Manhattan Study. Gardener and her colleagues found that people who drink diet soda every day have the greatest risk of stroke when compared to people who do not drink any soda.

But some are skeptical.

“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.

For the soda study, researchers asked participants how much and what kind of soda they drank. Participants were then grouped into seven categories: no soda (meaning less than one soda of any kind per month); moderate regular soda only (between one per month and six per week), daily regular soda (at least one per day); moderate diet soda only; daily diet soda only; and two groups of people who drink both types: moderate diet and any regular, and daily diet with any regular.

About 900 study participants reported drinking no soda at the start of the study, while 163 said they drank one or more daily.

Researchers followed up with participants for an average of 9.3 years. During that time, 559 suffered a vascular event, such as an ischemic or hemorrhagic stroke, both of which is caused by the rupture of a weakened blood vessel.

“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 told ABC News. “It is difficult to imagine that people’s intake of soda is constant during that period.”

Nonetheless, researchers say the results held up, and that even after accounting for age, sex, race and lifestyle choices such as smoking, exercise, alcohol consumption and caloric intake, the increased risk was still 48 percent higher for people who drank diet soda.

The study noted that researchers did lack data on what brands of soda participants drank and whether the soda contained artificial color or flavoring.