Introduction 

You’ve likely seen the words “sugar-free” and “no added sugars” on countless products in supermarkets, including chewing gum, sweets, and soft drinks. Thanks to sweeteners, many of these products can be consumed with a fraction of the calories. In 2022, it was reported that 3.4 million people in Great Britain consumed artificial sweeteners more than twice a day.

Xylitol is a natural sweetener which has gained popularity over the past decades, with production increasing over 40 times since 1978.¹ A study with over 3,000 participants from June 2024 has found that increased xylitol levels in human blood are linked to a higher risk of developing heart attacks and strokes.² 

However, as the authors point out, the xylitol concentrations observed were not from dietary sources, but naturally produced by the body during metabolism. Further analysis of 10 human plasma samples showed that consuming xylitol makes it easier for platelets to form blood clots. But is this the end of the story? 

Xylitol

Xylitol is a compound known as a polyol, or sugar alcohol with a chemical formula of C₅H₁₂O₅. It’s found in many foods, including berries, mushrooms, and corn husks. The human body also produces anywhere from a teaspoon to a tablespoon of this chemical every day when breaking down glucose.³ It was first discovered in 1890 by Emil Fischer as a syrup from beech wood.¹ 

Xylitol has the same sweetness as table sugar (sucrose), and takes on the same white, crystalline powder appearance. While a teaspoon of xylitol contains 2.4 calories per gram, the same amount of sucrose has about 4 calories. Xylitol can be used to cook and bake, or added to drinks. Although this sweetener is fine for human consumption, it can be fatal if consumed by dogs. 

Chemical structure of xylitol. Source: Wikimedia Commons by Kemikungen

Potential benefits 

Unlike sugar, this sweetener hardly increases blood glucose levels, making it a suitable alternative for diabetics.^4-6 Xylitol can also increase sensitivity to insulin, reducing the chance of developing diabetes.⁶ Studies have shown that consuming xylitol can reduce low-density lipoproteins (LDL), compared to those who don’t.^4,5 LDL is often referred to as ‘bad cholesterol’ because it can form plaques along blood vessels, causing them to narrow. Eventually, this can result in a heart attack or stroke. 

Another study has also shown that xylitol may help reduce the amount of fat around internal organs.⁶ This makes it suitable for people with obesity and can help reduce cardiovascular risk.

Xylitol is often discussed due to its tooth cavity-preventing abilities.^{1, 7} However, due to flaws in study designs, it’s unclear whether this is a direct effect of xylitol, or if other factors are at play.⁸ 

Poor quality evidence has shown that using xylitol in fluoride toothpaste could help prevent tooth decay.⁸ Xylitol might work by stopping the growth of S.mutans, a bacteria which causes cavities. However, this bacteria can become resistant to the sweetener in people who regularly consume it.⁹ The observed anti-cavity properties of xylitol could also be due to:⁸

• Chewing gum and sucking lozenges increasing saliva production in the mouth, which naturally helps to protect against cavities due to its antimicrobial and buffering properties
• A reduction in sugar consumption naturally reduces cavity formation

Metabolism

Xylitol is mainly broken down by the liver, although red blood cells and the kidney can further metabolise the sweetener.^7,10 Once broken down, it can be used to make biomolecules, like DNA nucleotides.⁷ Xylitol can also be made in the human body by breaking down glucose.³ 

Diagram of the human digestive system. Source: Wikimedia Commons by Mariana Ruiz, Jmarchn

Xylitol is poorly absorbed by the small intestine, so it often passes into the large intestine, where fermentation by bacteria occurs.⁷ This can result in bloating and flatulence. If too much xylitol is consumed, a phenomenon known as osmotic diarrhoea can occur.⁷ This is because the body can no longer absorb the sweetener, and it sits in the gut. This causes water to be drawn in, and in turn, the body attempts to flush xylitol from its system.⁷ 

Generally, adults can tolerate about 10-30 g of this sweetener, although up to 200 g can be tolerated if the amount is built up gradually.⁷

Heart attack and stroke

A heart attack occurs when the blood supply to the heart is cut off. This is typically caused by a blood clot in a coronary artery, which can partially or entirely block the vessel. As a result, the blood vessel becomes narrower and it becomes more difficult for blood to reach the organ. 

Similarly, a stroke occurs when blood doesn’t reach the brain. 85% of strokes are ischemic, occurring when a blood clot cuts off blood supply to the brain. Strokes can also be caused by a haemorrhage, which happens when a blood vessel bringing blood to the brain becomes weak and bursts. Both conditions may be fatal.

Potential link

The first study looking at the effect of xylitol on cardiovascular health was published in June 2024.² 

Endogenous xylitol

The authors began by looking at the xylitol levels naturally found in the body (endogenous), rather than xylitol from the diet (exogenous). In a study of over 3,000 participants, the authors confirmed a higher risk of heart attack and stroke in people with increased xylitol in their blood plasma.  

The authors also looked at plasma from 4 healthy participants who were given a xylitol drink. After a 12-hour fast, samples showed that endogenous levels of xylitol increased the activation of platelets. This enables their aggregation (joining together) to form a clot and may contribute to the risk of heart attack and stroke. The authors also looked at whole blood samples and found that xylitol helped to initiate the formation of blood clots.² 

Dietary xylitol

To look at the effect of xylitol on the diet, researchers studied the plasma and platelets of participants 30 minutes before and after xylitol consumption. The authors noted increased platelet activation in each of the participants, with the greatest aggregation in those with the highest xylitol plasma levels.²

Non-human models

The authors injected xylitol into the abdominal lining to observe the effects on blood clot formation in the body. Results showed increased clotting in study subjects who had been given xylitol, compared to those who had not.² 

Limitations

Although this data may seem concerning, this study does not provide enough evidence to suggest dietary xylitol increases the risk of a stroke or heart attack. Here are some things to note:

• Most of the samples in this study contained endogenous xylitol, not xylitol from dietary consumption. Even when dietary xylitol was studied, this was done 30 minutes after consumption, when levels were 1000 times greater than what is normally found in the blood
• Only 10 participants were used to look at the effects of xylitol consumption, which is far too small of a sample size to draw any definitive conclusions
• Most of the participants used in the observational studies were at risk of or had already experienced a stroke or heart attack. 22% had diabetes, which is linked to increased activity of the pathway that produces xylitol in the body.¹¹ As such, this may have caused an increase in plasma xylitol levels, making it seem that xylitol was the contributing factor
• The xylitol was provided in drink form for this study. When this sweetener is taken in liquid form, less is absorbed by the small intestines, and it ends up in the large intestine⁷ rather than flowing through the bloodstream. This means that the blood concentrations of xylitol are likely different to what would be expected if the participants consumed the sweetener in food 

Summary

Xylitol, a natural sweetener found in many foods and used in sugar-free products, has gained popularity due to its lower calorie content and benefits for diabetics and oral health. It can be broken down in the body, mainly in the liver. A recent study has found a link between high endogenous xylitol levels in blood and increased risk of heart attacks and strokes. The study also showed that xylitol consumption might enhance blood clot formation. However, the limitations of this study make it difficult to draw any direct conclusions between the sweeteners and these cardiovascular events.