Service members who consumed three or more energy drinks daily on a combat deployment in Afghanistan had more trouble sleeping at night and staying awake during the day, according to a newly released study.

They were significantly more likely to report sometimes or often falling asleep while in briefings or on guard duty. Nearly 40 percent of them reported getting less than four hours of sleep nightly. “The marketing of these types of drinks as energy boosters together with their availability in the combat environment makes it easy for service members to consume them in large volumes,” the study finds.

Red Bull, Monster and 5-Hour Energy were listed as examples of high-caffeine products the service members consumed. Energy drinks are free in dining facilities and available for purchase at convenience stores.

“This study suggests that high levels of energy drink consumption might indirectly impair performance in a military setting,” the researchers state.

Service members should be taught the long-term health effects of energy drinks are unknown, and that consuming higher amounts of them might affect mission performance and sleep, states the study released by the Centers for Disease Control and Prevention.

The study does not recommend a maximum level of daily energy drink consumption.

It states service members who drank one or two of the beverages each day reported improved cognitive performance and did not have the sleep problems reported by those who consumed three or more energy drinks daily.

The first-of-its kind look at energy drink consumption and its association with sleep problems during combat deployment is based on a 2010 survey of 988 men serving in Army and Marine platoons in support of Operation Enduring Freedom. Walter Reed Army Institute of Research analyzed data collected by Joint Mental Health Advisory Team 7.

Of the men surveyed, 545 said they consumed no energy drinks; 306 said they had one to two energy drinks daily; and 137 reported drinking three or more energy drinks daily.

An estimated 6 percent of young adults consume energy drinks daily compared with 45 percent of the service members surveyed. “This might reflect the unique and extreme demands of a combat deployment and the widespread availabity of energy drinks,” the study authors state in an editorial note.

Rose Alexander, spokeswoman for Joint Base Charleston, said energy drink consumption is a personal preference. “We don’t track something like that,” she said.

The Ralph H. Johnson VA Medical Center had no comment on the study.