A team of researchers including Dr. Stanley Hazen, chair of cardiovascular and metabolic sciences at the Cleveland Clinic Lerner Research Institute, identified an association between high levels of circulating xylitol and an elevated three-year risk of cardiovascular events in an analysis of more than 3,300 patients. The findings were published last week in the European Heart Journal. 

“People whose levels of xylitol were in the top 25% of our population—the top quarter—they were at double the risk for a heart attack, stroke, and death than people whose levels were in the bottom quartile,” Hazen tells Fortune. “Our data is entirely consistent with xylitol being a prothrombotic compound (prone to causing blood clots), and it enhances cardiovascular risk—the very compound that we are often recommending to patients to use as a sugar substitute, particularly if they’re diabetic.”

In another part of the study, subjects were asked to drink xylitol-sweetened water. The amount of xylitol in each drink was comparable to that found in a serving of keto ice cream or diabetic cookies, Hazen says. Researchers then examined subjects’ blood platelets, or thrombocytes, the cell fragments that form clots.

“After drinking this typical exposure, blood levels went up over 1,000-fold, to superphysiologic levels,” Hazen says. “They stayed elevated into this high range—which is associated with higher cardiovascular disease risk—for the next four to six hours in every volunteer examined, and every platelet functional measure we looked at was substantially increased.”

This discovery comes just over a year after Hazen and his colleagues found a similar relationship between the artificial sweetener erythritol and cardiovascular event risk. In the U.S., xylitol isn’t as common as erythritol in keto or sugar-free foods, according to a Cleveland Clinic news release. It is, however, abundant in other countries.

What is xylitol?

Xylitol is sometimes labeled as sugar alcohol, so named because parts of its chemical structure resemble those of sugar and alcohol. Also called polyols, sugar alcohols are carbohydrates that occur naturally in some fruits and vegetables. They don’t contain ethanol, the type of alcohol in alcoholic beverages.

Sugar alcohols are popular sugar substitutes because they taste sweet but have fewer calories per gram than sugar, according to the Food and Drug Administration (FDA). They’re typically used in combination with artificial sweeteners, and can be commercially produced from sugars and starch.

Sugar alcohols prevent browning, help retain moisture, and add bulk and texture, per the FDA, making them an ideal ingredient in processed foods such as baked goods. Your body can’t completely absorb sugar alcohols, which is why consuming them doesn’t make your blood glucose spike like regular sugar does.

That cooling sensation in your mouth after brushing your teeth? It’s an indication of high sugar alcohol concentrations. Because sugar alcohols don’t cause cavities, they’re popular in oral care products. Xylitol in particular is common in chewing gum. 

As demand for low-sugar, low-calorie foods increases, the sugar alcohol market continues to boom. It’s expected to exceed $1.8 billion by 2033, according to Persistence Market Research. Xylitol, also called birch or wood sugar, boasts low production costs that are another industry boon, Hazen says.

“[Xylitol] is literally made out of wood pulp and sawdust. It’s cheaper to make xylitol than to isolate cane sugar out of sugarcane,” Hazen tells Fortune. “And it tastes just like sugar—equal sweetness, it’s granular—so it has a lot of things going for it.”

These factors are also what makes xylitol so dangerous, he says.

Tatsiana Niamera—Getty Images

What foods contain xylitol?

According to the FDA, the sugar substitute can be found in a number of food and other products, including:

• Baked goods
• Breath mints
• Children’s and adult chewable vitamins
• Cough syrup
• Dietary supplements
• Mouthwash
• Over-the-counter medicines
• Some peanut and nut butters
• Sugar-free desserts, including “skinny” ice cream
• Toothpaste

Is it safe to use sugar substitutes?

Last year, the World Health Organization advised against using nonsugar sweeteners, particularly as a means of weight management. As calorie-containing sugar derivatives, sugar alcohols were excluded from the agency’s new guidance. Still, the decree marked a shift in how consumers view their relationship with sugar and its substitutes.

The nonprofit food watchdog Center for Science in the Public Interest recommends cutting back on xylitol, citing the fact that large amounts may lead to diarrhea. (In humans, that is; xylitol is deadly for dogs.) Hazen would rather you cut it out altogether.

“If [you] want to sweeten something, at this point I think it’s better to use sugar or honey or fruit, and in moderation,” he says. “If you’re diabetic, you monitor your blood sugar.”

Consult your doctor and/or nutritionist before making any drastic changes to your diet.

Given the intricacies of cardiovascular disease and the limitations of Hazen’s research, it would be a stretch to conclude that xylitol causes events such as stroke and heart attack, he says. Additional long-term studies are warranted. For example, it’s unclear whether adolescents who frequently consume sugar substitutes will develop a higher risk of a cardiovascular event than their peers who don’t.

In the meantime, Hazen is concerned enough about the health hazards of xylitol that he’s advocating for nutrition label overhauls.

“It’s a big public health issue,” he says. “We need to really be trying to lobby and get regulatory changes so that it’s no longer generally recognized as safe.”

For more on sugar substitutes:

• Calorie-free sweetener linked to heart attacks, strokes, and blood clots, scientists find in study
• Aspartame may be a ‘possible carcinogen.’ Here are 8 common drinks and foods containing the sweetener
• No, drinking Diet Coke won’t kill you, but experts say there are several good reasons to consider cutting back
• Coca-Cola CEO says company has outmaneuvered Ozempic because it’s been preparing for a low-calorie future for years