People who think sugary drinks are a pick-me-up may be in for a letdown: New research finds sweetened beverages actually boost sleepiness.

"People wishing to alleviate sleepiness through the consumption of a high-sugar, low-caffeine content energy drink -- erroneously believing the 'sugar rush' to be effective -- should avoid drinks that have little or no caffeine," said study co-author Clare Anderson, from the Sleep Research Centre at Loughborough University in the United Kingdom. "It is caffeine that is particularly effective for alleviating sleepiness, not sugar," she added.

Anderson and her colleague Jim Horne found that, one hour after drinking a high-sugar, low-caffeine drink, people had slower reaction times and experienced more lapses in concentration than if they had consumed a caffeine- and sugar-free beverage.

They reported the findings in the July online edition of Human Psychopharmacology: Clinical and Experimental.

As Anderson explained, "Many soft drinks contain large amounts of sugar, and previous findings had indicated that such large amounts may improve cognitive performance. However, these effects were almost immediate."

The real question, for Anderson, was whether that quick boost had any longer-term effect beyond the first 15 minutes after the so-called sugar rush disappeared.

To help answer that, she and Horne had 10 healthy adults restrict their sleep to just five hours on the day prior to the trial. Then, 60 minutes after eating a light lunch, these healthy adults were given either a high-sugar, low-caffeine energy drink (42 grams of sugar plus 30 milligrams caffeine) or an identically tasting zero-sugar drink used as a placebo. Forty-two grams of sugar is equal to about 8 teaspoons, Anderson said.

The participants were next asked to complete a 90-minute test during the afternoon low-energy period. The test assessed their level of sleepiness and ability to concentrate.

"Around 70 minutes after consumption, there was a worsening of sleepiness --delayed reaction time, increased lapses in attention -- following the consumption of a high-sugar drink, in comparison to a placebo," Anderson said.

Her conclusion: Highly-sugared drinks without caffeine do not counteract sleepiness beyond perhaps a short sugar rush. In fact, they appear to boost drowsiness.

"These drinks are of little benefit to sleepy people," Anderson said. "Caffeinated drinks, even sugary ones, are much better for counteracting detrimental effects of sleepiness."

One nutrition expert agreed that sugar won't help push energy levels past the initial minutes-long sugar rush, and even caffeine won't help you stay awake beyond a few hours.

"Energy drinks are a misnomer," said Lona Sandon, an assistant professor of clinical nutrition at the University of Texas Southwestern Medical Center at Dallas and spokeswoman for the American Dietetic Association. "Sure, they provide energy in the form of calories, usually from some form of a simple sugar," she added.

Sandon explained that simple sugars are digested, absorbed and metabolized very quickly, so the energy they contain doesn't last long. "Some energy drinks may have just enough caffeine to stimulate your central nervous system and give you a false sense of feeling energized for a short period of time," Sandon said. "Keep in mind, a dose of caffeine large enough to have an energizing effect -- about 1 regular soda or cup of coffee -- will only last about 3 hours."

According to the Texas expert, there is a more lasting and healthy means of staying fresh: good sleep and a healthful diet.

"To improve a feeling of having energy, start by getting plenty of rest, fluids, and fuel your body with quality nutrients from fresh fruits, vegetables, whole grains and lean protein sources," Sandon said. "A balanced diet, including carbohydrate, fat, and protein, will keep you feeling satisfied longer."