Drinking diet fizzy drinks could be contributing to rising anxiety levels, scientists have warned, after a study on mice found that the artificial sweetener aspartame triggered anxious behaviour and altered brain regions linked to fear.
Researchers at Florida State University gave mice aspartame in their drinking water at levels equivalent to two to four small cans of diet fizzy drinks per day for humans. The mice displayed clear anxiety-like behaviour, such as staying close to the walls in an open-field test, and showed genetic changes in the amygdala, the brain area that processes threats and triggers the fight-or-flight response.
Lead author Sara Jones said: “It was such a robust anxiety-like trait that I don’t think any of us were anticipating we would see. It was completely unexpected. Usually you see subtle changes.” The study, led by Dr Pradeep Bhide of the university’s Centre for Brain Repair, originally aimed to investigate nicotine’s effects but shifted focus after observing the sweetener’s impact.
Dr Bhide noted: “The anxiety appeared to be robust, and I would not rule out that smaller amounts… could produce anxiety in mice and men, if consumed daily over a period of several weeks.” The researchers also found that male mice passed on the brain changes to their offspring, suggesting anxiety could be inherited, though the effect would dilute with each generation.
Aspartame, discovered accidentally in 1965 and used in diet drinks since the 1980s, is 200 times sweeter than sugar. A regular 330ml can of Coke Zero contains around 180–200mg. The FDA recommends a maximum daily intake of 40mg per kg of body weight, meaning a 70kg adult could safely consume up to 280g per day. However, the study suggests that even doses below this limit could cause neurobehavioral changes in humans and their descendants, potentially affecting a larger population than currently thought.
The findings, published in the journal Scientific Reports, could pave the way for further research into diet drinks’ effects on human mental health. Food safety organisations worldwide have generally deemed aspartame safe, but this study raises new concerns about its potential link to anxiety.
