The study, conducted by psychologists at the Walter Reed Army Institute of Research, followed more than 600 combat soldiers in their first seven months home after deployment. The report, published in Military Medicine, concluded drinking two or more energy drinks a day "was significantly related to mental health problems, aggressive behaviors, and fatigue in a military population following a combat deployment."
Dr. Amy Adler, a senior psychologist and lead author of the report, tells ABC11 she hopes the study provokes a more in-depth look at how caffeine affects people in both military and civilian life.
"There may be other high-risk groups out there like police, firefighters, emergency responders, or other groups this may apply to - or not," Dr. Adler explains. "These groups are groups we want to pay attention to because there might be a way to mitigate the mental health problems out there."
Energy Drinks 'Part of the 21st Century GI Identity'
Veterans of the Vietnam War might remember how every soldier carried a pack of smokes, but veterans of the wars in Iraq and Afghanistan are now describing a culture where every soldier gulps down an energy drink.
"They were rampant," Greg Gebhardt, an Iraq veteran living in Raleigh, recalls to ABC11. "It was almost like a lifestyle. The soldiers used to joke as long as we have an armed forces in the United States, the tobacco industry and energy drink industry will be just fine."
WATCH: How much caffeine is too much?
Gebhardt was among the leaders of base operations at Camp Victory Iraq in Baghdad. Part of his responsibilities included managing dining facility operations, which Gebhardt says always made available caffeinated energy drinks like Rip It and Wild Tiger.
They weren't known for their taste, but instead, Gebhardt says his comrades relied on the caffeine in the field.
"I think it served a purpose to give it that extra boost, to push them a little further, to keep their cognitive functions about them for that 16th or 18th hour of a long day in 120-degree heat."
Energy drinks - some with three times the amount of caffeine as soda - was also a better alternative to other products or substances soldiers could find downrange.
"The thought is if you don't have your faculties about you, if you're using illicit substances, then people's lives are at risk."
By her own admission, Dr. Amy Adler says her team of researchers had not set out to investigate energy drinks. Instead, they were simply tasked with following combat soldiers to learn more about their transition home. After a few days of observations, though, Adler explains the team noticed the prevalence of energy drink use and decided to ask about it in a survey.
"Everyone can drink coffee and everyone can have tea or a soda - something with caffeine," Adler asserts. "But we wondered about the sheer prevalence of (caffeinated energy drinks) because the soldiers are pretty young. For us, we're behavioral health researchers, so we're always looking for risk factors or potential moderators of mental health outcomes."
The survey generated responses from more than 600 soldiers who had just returned from a year-long deployment in Afghanistan, and an astounding 75% responded positively to the question of whether they drank energy drinks. A smaller percentage, about one in six soldiers (16%), reported consistently drinking at least two energy drinks per day.
Adler's team then asked about mental health issues like post-traumatic stress, fatigue, aggression and sleep deprivation. The survey results offered a stark difference: the soldiers drinking two energy drinks or more per day were more likely to have mental health problems than those who didn't.
"Depression and sleep problems, increased aggression, anxiety, substance abuse, things like that. All of those are risk factors and many of these were associated with drinking excessive amounts of energy drinks."
Still, the link isn't totally defined; Adler's team doesn't claim energy drink consumption leads to PTSD, in fact, it's also possible that those who experience mental health problems are choosing to drink energy drinks. The bottom line, however, is that according to Adler there is now a "clue" about an effective treatment that also gives some element of control to soldiers wanting to help themselves.
"What we're interested in doing is identifying anything that might be something they could engage in actively that could make them feel better," Adler explains. "It is something that soldiers can manage themselves, it is something that a family can pay attention to or a leader can pay attention to. It gives them a tool of something they can do to help manage some of the symptoms when they get back."
Caffeine concerns: How much is too much?
Soldiers are not the only ones consuming energy drinks; several caffeinated products are attractive to teens and adults who are studying and working long hours.
The National Center for Complementary and Integrative Health, a division of the U.S. Department of Health and Human Services, reports men between the ages of 18 and 34 years consume the most energy drinks, and almost one-third of teens between 12 and 17 years drink them regularly.
Dr. Branson Page, a physician at WakeMed's Emergency Department, tells ABC11 many people underestimate the risks of consuming too much caffeine.
"Kids don't see any limit. If a little bit is good, a lot must be better. You just keep drinking it. It's going to make you more agitated and much more anxious."
According to WakeMed, 47 patients between the ages of 13-22 were treated for adverse effects of caffeinated energy drinks, a connection that Dr. Page says is not obvious to the patient upon his/her arrival.
"They don't typically come in and say, 'Hey I just had four energy drinks and I feel bad.'" he told ABC11.
Dr. Page recommends people shouldn't consume more than 400 mg of caffeine per day; most 16-ounce cans of energy drinks contain about 160 mg (a soda averages 50mg). Coffee, actually, contains much more caffeine. In fact an 8-ounce cup of Starbucks coffee - the smallest cup offered and less than have liquid in an energy drink - has 155 mg of caffeine.
"Caffeine is a central nervous system stimulant," Dr. Page adds. "It elevates your heart rate, it increases blood flow. Under the normal dosing amount, that's fine. It's going to make you more alert and more active. Too much of that is going to increase anxiety, increase agitation, cause erythema, palpitations, and real physical symptoms."
To avoid those symptoms, Dr. Page suggests several healthy alternatives to caffeine, starting with daily exercise.
"You have to change your behavior," he said. "We undervalue the benefit (exercise) has on mental awareness and ability to stay awake during the day and ability to sleep at night."