"Sugar rushes" from such drinks don't appear to be very effective at overcoming sleepiness, write Clare Anderson, BSc, PhD, and colleagues in Human Psychopharmacology.
Anderson is a lecturer in the human sciences department of England's Loughborough University. Her study included 10 healthy young adults (average age: 22 years) without sleep problems.
Participants agreed to sleep for only five hours before taking an attention test, in which they clicked a button when a clock appeared on the computer screen.
After their short night's sleep, participants ate their usual breakfast and headed to the researchers' lab. They hadn't consumed alcohol or caffeine during the previous day. They also wore activity monitors on their wrists to confirm that they hadn't broken the five-hour sleep limit.
At the lab, the researchers fed each participant a can of minestrone soup for lunch. They also gave them either a high-sugar, low-caffeine, lightly carbonated energy drink or a sugar-free, caffeine-free, lightly carbonated drink.
Both drinks tasted the same, and participants didn't know which was which. They took the test twice, waiting a week between tests, drinking the energy drink in one session and the ordinary drink in the other session.
After downing the drinks, participants took the attention test. Their scores were similar with both drinks. About 70 minutes after drinking the high-sugar, low-caffeine energy drink, their attention scores began to lag behind their scores with the sugar-free, caffeine-free drink.
Neither drink was high in caffeine. But based on previous studies by other researchers, Anderson and colleagues conclude that caffeine is probably more helpful than sugar in helping sleepy people pay attention, especially when followed by a short nap.