In recent years, there has been an increase in cases in the UK and Ireland of children becoming seriously ill soon after drinking sugar-free slushies. A new study points the finger at glycerin, a compound used as a sugar substitute that has until now been considered safe.
Glycerin is a versatile compound used in a wide range of food, personal care, medical and pharmaceutical industries. In food and beverages, it is often used as a thickening agent, preservative, and sugar substitute. In 2017, the European Food Safety Authority (EFSA) re-evaluated the safety of glycerol as a food additive (named E422) and found that it has "low acute toxicity".
However, a new study led by Birmingham Women's and Children's NHS Foundation Trust looked at cases in 21 children in the UK and Ireland who became seriously unwell shortly after drinking sugar-free slushies containing glycerin between 2009 and 2024.
The researchers said: "Shaved ice slush drinks are popular, brightly colored soft drinks designed to appeal to children and young people. The ingredients of slushie drinks vary, but most slushie drinks sold on the market in the UK and Ireland are advertised as 'no added sugar' or 'sugar-free'. Sugar-free or sugar-free varieties contain glycerol (E422) to maintain the slushy effect. The patients reported here all became ill shortly after drinking slush drinks containing glycerin."
Eighteen of 21 patients provided gender information: 54% were male and 44% were female. The average age of patients when they presented to the emergency department was three and a half years old, but ranged from two to nearly seven years old. Fifteen patients provided information on onset of illness: 93% experienced discomfort within one hour of ingesting the smoothie.
Of the 17 patients who were able to provide information on their level of consciousness, 94% experienced a sharp decline in consciousness. A child developed a tonic-clonic seizure, which causes stiffness and rhythmic jerking of the body. Twenty children (95%) experienced hypoglycemia or hypoglycemia; 65% of these children experienced severe hypoglycemia. The median blood glucose level was 1.2 mmol/L (21.6 mg/dL), while the lower limit of normal was 3.9 mmol/L (70 mg/dL).
94% of patients presented with metabolic acidosis, a condition in which the blood becomes too acidic due to a buildup of acid. Normally, the body controls blood pH within a small range (about 7.35 to 7.45), but in this study, the median pH at the onset of the disease was 7.21. Additionally, almost all patients (95%) had elevated lactate levels, and 12 of 16 children had hypokalemia. Based on these symptoms, the researchers determined that the children had glycerol intoxication syndrome (GIS).
"The syndrome of glycerol toxicity is not well defined; few cases have been reported in the literature, and the specific pathophysiology remains unclear. The onset in adults is triggered by rapid and large-dose ingestion of glycerol, with or without catabolism, and is characterized by metabolic acidosis and somnolence, which may progress to coma and seizures," the researchers said.
Catabolism is the process by which the body breaks down molecules to release energy. In the case of glycerol poisoning, catabolism indicates that the body is in "emergency mode," breaking down too much too quickly, leading to dangerous acid buildup.
The researchers said: "Although slushie drinks have been around for some time, there are currently no published medical reports of these related GIS. One reason for the recent apparent surge in cases may be that the sugar content of these drinks has been reduced, which is mainly due to two factors: first, public health and parental concerns about high sugar intake, and second, the introduction of 'sugar tax' on high sugar drinks in Ireland and the United Kingdom in 2018 and 2019 respectively."
All children responded quickly to initial treatment and correction of hypoglycemia, and they were discharged from the hospital after being advised to avoid slushies. Twenty children followed this advice and experienced no further symptoms of hypoglycemia. But one of the children drank a slushie a few years later (at age 7) and quickly developed symptoms of hypoglycemia again, progressing to vomiting and lethargy. Their parents gave their children a glucose drink and called an ambulance. When the ambulance arrived, the child's blood sugar had returned to normal and his symptoms began to ease.
In light of the rise in cases in the UK, the UK Food Standards Agency (FSA) and Food Standards Scotland (FSS) have published new voluntary industry guidance on glycerin in smoothies, advising that smoothies should not be sold to children aged four and under, and that children under ten should not be offered free refills in any promotions.
Discussing the results of this study, the researchers said slush has no nutritional value and does not offer any health benefits, so recommendations regarding its consumption should focus on safety.
"Transparency of glycerin concentrations in slush drinks is low; therefore, estimating safe doses is not easy. The rate and dose of intake, as well as other aspects such as whether the drink is consumed with a meal or in an empty stomach, or after high-intensity exercise, may also be triggers," said the study's researchers.
Researchers recommend that no matter your age (especially if you're a child), drink less ice-cold drinks.
The research was published in the journal Archives of Disease in Children.