Caffeine concern over teens and energy drinks One in three teenagers consumes the equivalent of 10 instant coffees a day in energy drinks that can cause insomnia, anxiety and heart problems, a leading sleep expert says. A survey of 110 patients conducted by Chris Seaton, a paediatric sleep specialist from the Westmead Children's Hospital, found 35 per cent of teenagers consume at least two energy drinks a day. A daily dose of caffeine should not exceed 200 to 300 milligrams, yet a 500 millilitre serving of Mother, Monster or Red Bull contains 160 milligrams of caffeine, and some teens drink three a day. "They are getting into it before school," Dr Seaton said. Health professionals are calling for tighter regulations on the availability of energy drinks which, with sales of $593 million a year, make up the fastest growing beverage sector. Teenagers are limited in getting alcohol and tobacco, but there is no limitation on energy drinks. It's a real free-for-all," Dr Seaton said. Caffeine in high doses is a toxic substance and there has been a couple of reported teenage deaths related to an overdose. The high sugar content in energy drinks is just as concerning, says Jane Martin, who leads the Obesity Policy Coalition. One 250-millilitre Red Bull contains the equivalent of 13 teaspoons of sugar.