Is caffeine in fizzy drinks making teenagers stupid?
Caffeine-laden fizzy drinks could be stopping children's brains from developing properly, scientists have warned.
They believe that by preventing deep sleep, caffeine interferes with the development of the brain during adolescence.
This is a critical time for the brain, when problems in development can lead to schizophrenia, anxiety, drug use and personality disorders.
Researchers experimented on rats, but say the findings raise concerns for children and teenagers, some of whom consume large amounts of caffeine from colas and energy drinks.
Between 300 and 400mg of caffeine - four cans of energy drink a day or three or four mugs of coffee - could make a difference, the study suggests.
A can of the popular energy drink Red Bull, for example, contains 80mg.
The Swiss research focused on the development of the brain during the teenage years. As it prepares for the demands of adulthood, synapses, or connections between cells, that are not needed are eliminated.
It is thought that sleep is crucial to this process. Professor Reto Huber, of the University Children's Hospital in Zurich, said: 'This optimisation presumably occurs during deep sleep.
'Key synapses extend, others are reduced; this makes the network more efficient and more powerful.'
Prof Huber said that when young rats were given caffeinated drinking water, they got less deep sleep than those who drank plain water.
Their brains also had more connections in them at the end of the study - meaning the pruning back process had been disturbed, the journal PLoS ONE reports.
A spokesman for the researchers said: 'Children's and young adults' average caffeine consumption has increased by more than 70 per cent over the past 30 years and an end to this is not in sight.
'The drinks industry is posting its fastest- growing sales in the segment of caffeine-laden energy drinks.
'The brain goes through a delicate maturing phase in puberty, during which many mental diseases can break out.
Another recent study suggested sugarladen fizzy drinks made children as young as five violent, withdrawn and distracted.