Energy drinks can provide a midday boost, but troops should be careful about their caffeine intake, according to the Pentagon.
"The amount of caffeine varies" among brands, Patricia Deuster said in a post for the Defense Health Agency, and nutrition labeling can be misleading.
Other ingredients in energy drinks, such as guarana (Brazilian cocoa), can also contain caffeine and make the actual caffeine content higher than that listed, said Deuster, director of the Consortium for Health and Military Performance at Uniformed Services University of the Health Sciences in Bethesda, Maryland.
"People don't realize that drinking a couple of energy drinks in a fairly short amount of time, like in one hour, can potentially harm them," Deuster said.
Chugging down high doses of caffeine and sugar in a short amount of time can overstimulate the central nervous system with short-term effects such as nervousness, shakiness, rapid heartbeat, irritability, or sleep issues, she said.
Maj. Sean Spanbauer, a performance dietitian for U.S. Army Special Operations Command, recommends limiting energy drink consumption to one or two per day, and no more than one in a four-hour period.
"A general rule of thumb is not consuming more than 400 milligrams of caffeine per day," said Spanbauer, or 200 milligrams every three to four hours. Most popular energy drinks contain about 80-120 milligrams of caffeine per eight-ounce serving, he said.
"In a deployed environment, if somebody is sleep deprived and mission critical, there are benefits to caffeine, so I would start with 200 milligrams but do not exceed 600 milligrams in one day," Spanbauer said.
A 2010 study by Walter Reed Army Institute of Research found that almost 45 percent of deployed service members drank at least one energy drink per day, and nearly 14 percent drank three or more a day. The long-term effects of consuming energy drinks regularly aren't known, but in the short term, sleep quality can be impacted.