Erythritol, a zero-calorie artificial sweetener widely used in low-sugar and keto products, has been linked in some patients to blood clotting and an increased risk of cardiovascular events, including heart attacks and strokes, according to a new study. The paper, published Monday in the journal Nature Medicine, found that older adults consuming high amounts of erythritol who were already at risk of heart disease were twice as likely to experience a heart attack or stroke. “It’s on par with the strongest of cardiac risk factors, like diabetes,” lead study author Dr. Stanley Hazen told CNN. In expanding their research, Hazen’s team at the Cleveland Clinic in Ohio also found that erythritol appeared to be causing clots in some animal and lab studies. Overall, Hazen cautioned, “The degree of risk was not modest.” But some researchers and nutritionists warned that further research is needed—on erythritol and beyond.“We have work to do on every single one of the artificial sweeteners,” Kimber Stanhope, a research nutritional biologist at UC Davis, told Stat News. “It’s ridiculous how understudied they are.”