New research shows that older women who drink too many diet drinks increase their risk of having a heart attack or stroke, illuminating a new risk factor of some of our biggest killers.

"Our findings are in line with and extend data from previous studies showing an association between diet drinks and metabolic syndrome," Dr. Ankur Vyas, a researcher at the University of Iowa and lead author of the new study, said in a press release. "We were interested in this research because there was a relative lack of data about diet drinks and cardiovascular outcomes and mortality."

The findings, which were presented at the American College of Cardiology’s annual meeting in Washington, D.C., suggests that postmenopausal women who drink two or more diet drinks per day are 30 percent more likely to suffer adverse cardiovascular events compared to peers who never or rarely consume diet drinks. These women were also 50 percent more likely to die from related diseases.

To investigate, Vyas and colleagues used data on diet drink consumption among patients enrolled in the Women’s Health Initiative Observational Study. The sample was then divided into three consumption groups: two or more diet drinks a day, five to seven per week, one to four per week, and zero to three drinks per month. A diet drink was defined as a 12-ounce diet soda or fruit beverage.

Within a decade, adverse cardiovascular events like heart attack and stroke had occurred in 8.5 percent of the first group, 6.9 percent of the second, 6.8 percent of the third, and 7.2 percent of the fourth. The correlation remained when the researchers controlled for body mass index, smoking habits, physical activity, salt intake, diabetes status, and other factors known to influence cardiovascular risk.

That said, the women who had more than two diet drinks per day were also more likely to be smokers and suffer from hypertension, diabetes, and obesity. "We only found an association, so we can't say that diet drinks cause these problems," Vyas cautioned.

Cardiovascular disease is currently the leading cause of death in the United States, killing about 600,000 people each year –– about one-fourth of all recorded fatalities. On average, deaths and illnesses associated with coronary heart disease cost the nation $109 billion annually.

While it’s important to keep causation and correlation separate, the findings definitely warrant further inquiry, Vyas told reporters. "It's too soon to tell people to change their behavior based on this study; however, based on these and other findings we have a responsibility to do more research to see what is going on and further define the relationship, if one truly exists," he explained. "This could have major public health implications."

Source: Vyas et al. Diet Drink Consumption and the Risk of Cardiovascular Events: A Report from the Women's Health Initiative. At the American College of Cardiology 63rd Annual Scientific Session. 2014.