U.S. military health officials are warning service members that chugging too many energy drinks can have harmful side effects.

Energy drinks come in small containers and extra-large cans with labels that promise increased energy and performance.

They became the beverage of choice over water for many service members during the wars in Afghanistan and Iraq. The Walter Reed Army Institute of Research analyzed data collected during Operation Enduring Freedom in 2010 and found that nearly 45 percent of deployed service members consumed at least one energy drink daily. Nearly 14 percent reported drinking three or more per day.

Many of the most popular energy drinks are heavily marketed to young people, including military members, and are readily available on military bases and downrange.

But there are real reasons to avoid overusing energy drinks, according to Patricia Deuster, professor and director of the Consortium for Health and Military Performance at the Uniformed Services University of the Health Sciences, in a U.S. Army press release.

Too Much Caffeine

Energy drinks are loaded with caffeine. Service members should avoid consuming more than 200 milligrams of caffeine every four hours, Deuster maintains.

Troops should add up the caffeine in their energy drinks, plus any other caffeinated beverages they may drink, such as coffee and soft drinks, she added.

"If it's got more than 200 milligrams of caffeine, don't use it," Deuster said.

Deuster also warns female service members to be cautious about using energy drinks, noting the amount of caffeine they ingest relative to their body weight is an issue for women.

"Women get a higher concentration [of caffeine], since they tend to be smaller," she said.

High amounts of caffeine can lead to increased blood pressure, panic attacks, heart palpitations, anxiety, dehydration, insomnia and even bowel irritability when energy drinks are mixed with alcohol, Deuster maintains.

Loaded With Sugar

Energy drinks are also loaded with sugar. Some cans pack a punch of 27 grams of sugar, two-thirds of the recommended daily maximum for men, and 2 grams more than the maximum doctors recommend for women. Some service members can double or even triple that if they drink more than one energy drink per day, Deuster said.

The Centers for Disease Control and Prevention recommend keeping your intake of added sugars to less than 10 percent of your total daily calories.

All of that extra sugar can cause blood-sugar levels to increase, but even the sugar-free versions of energy drinks can lead to weight gain, as research suggests artificial sweeteners may raise blood sugar as well, the release states.

And while they have nutritional labels, energy drinks are not regulated as dietary supplements and many do not list supplement information.

Questions About Taurine

One area that's concerning to Deuster is the ingredient taurine. The chemical compound is an amino acid found in animal tissue. Many energy drink makers purport the ingredient will enhance mental and physical performance, but researchers with the Department of Veterans Affairs Medical Center report that little actually is known about taurine's neuroendocrine effects.

"Doctors don't know what the effects of [energy drink] ingredients are in larger doses," Deuster noted. "I don't think anybody has an answer to the long-term effects question."

Energy drinks have become popular mixers for alcohol, raising other concerns for health experts.

"A lot of the young people mix energy drinks with alcoholic beverages; then you've got a wide-awake drunk," Deuster says.

The CDC warns that when alcoholic beverages are mixed with energy drinks, the caffeine stimulant can mask the effects of the alcohol, which is a depressant. Often, the person drinking doesn't realize that he's actually drunk.

People who mix alcohol with energy drinks are three times more likely to binge drink than those who don't mix alcohol with energy drinks, according to the CDC.

Some companies sell pre-mixed alcoholic energy drinks that have the same sweet or tart flavors as standard energy drinks. The alcohol content in these beverages can be significantly higher than that of beer, Army officials maintain.

Sleep Problems

There is also a problem in the military with energy drinks and sleep, according to Deuster. While service members may initially use energy drinks to make up for a lack of sleep, they can easily overuse the drinks, leading to a harmful cycle. Excessive consumption of energy drinks can cause sleep problems and hamper performance, she said.

Caffeine can be effective when used properly, but "because caffeine impairs sleep, individuals should stop all caffeine consumption at least six hours prior to scheduled sleep. Otherwise, sleep could be impaired without the person even being aware of it," according to Nancy J. Wesensten of the Center for Military Psychiatry and Neurosciences Research.

The CDC reports that service members who drink three or more energy drinks per day are significantly more likely to report sleeping fewer than four hours per night. They are also more likely to report disrupted sleep and other illnesses.

"Lack of sleep can impact memory and a service member's ability to pay attention when it matters most," Army officials maintain. "Research indicates service members who drank three or more energy drinks each day also had difficulty staying awake during briefings or on guard duty."

-- Matthew Cox can be reached at matthew.cox@military.com.