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Consumer Reports analyzed 12 popular carbonated energy drinks for caffeine and calorie content, and found caffeine levels, which often aren't listed on the label, can top 200 milligrams per bottle or can. Meanwhile, the calorie count may reach up to 260 calories.
Caffeine intake up to about 300 milligrams a day is considered OK for most healthy adults; children should be limited to well under 100 milligrams.
Part of the problem is that many energy drinks list their nutritional content on the label per 8-ounce serving. But the bottles or cans often contain more than that, and very few people stop drinking halfway. Can you imagine drinking more than one of these drinks on top of all other drinks you may consume daily?
Aside from caffeine and sugar, some of the more common ingredients are taurine, ginseng, guarana, vitamins, and green tea.
"Most of the energy drinks contain high-tech-sounding ingredients that are not controlled substances, of no value, and potentially harmful" in large amounts, comments Cynthia Sass, MPH, MA, RD, a board-certified specialist in sports dietetics.
And trying to figure out exactly how much of each stimulant is contained in an energy drink can be difficult, she says.
"Energy drinks contain multiple stimulants that, when combined, can be dangerous and have a very powerful effect on the body," says Sass. Most people know how much caffeine they can tolerate, but may not be familiar with the effects of some of the other ingredients.
She describes such possible symptoms as upset stomach, leg weakness, heart palpitations, being jittery, nervousness, and more. Drink these energy drinks on an empty stomach and the effects can be magnified.
"There will be an energy burst, but it could also lead to agitation, difficulty concentrating, hyperactivity, a problem sleeping, nausea, and affect blood pressure," points out Suzanne Farrell, MS, RD, a spokeswoman for the American Dietetic Association.
As far as blood pressure goes, study conducted by Wayne State University researchers at Henry Ford Hospital in Detroit, Michigan, studied a small sample of 15 healthy people with average age of 26. For a week, they had to stay away from any other form of caffeine two days prior to the study and during the study, and drink two cans of an energy drink with 80 milligrams of caffeine each day.
Findings showed that drinking just two cans of energy drink in a day without adding any other caffeinated drinks increased blood pressure to the study participants and their heart rate in just four hours.
On the first day, participants found their systolic blood pressure rise by nine points; by the end of the study, it had risen to 10 points. Both times their Diastolic blood pressure (the lower number) had risen 5 points.
Their heart rates had also gone up by five beats per minute on the first day and on the last day, when they were relaxing and watching a movie, it had gone up by seven beats per minute.
James Kalus, Pharm.D., senior manager of Patient Care Services at Henry Ford Hospital in Detroit, Mich., and a former Wayne State researcher who led the study feels that the increases in blood pressure and heart rate may be due to the caffeine and taurine in the drinks. However, some of the other energy drinks contain much higher levels of caffeine, he said.
"Thousands of young adults are using these drinks," Kalus said. "Some are mixing the energy drinks with alcohol. We don't necessarily know how much they are drinking at a time or whether they are drinking before exerting themselves playing basketball or dancing."
Some of the marketing for energy drinks is combined with extreme sports, he said. The researchers are unsure what effect exercise or the combination with alcohol has on a person who drinks energy drinks; however, some countries advise against using energy drinks to quench thirst while playing sports.
Blood pressure and heart rate naturally go up during physical activity, Kalus said. "This could be further augmented by energy drinks. Energy drinks could affect some individuals if they didn't know they had a problem in the first place," he said. "The study raises some concerns."
Until further study, Kalus said people with high blood pressure or heart disease should avoid energy drinks because they could affect their blood pressure and may even alter the effectiveness of their medications.
Researchers say the bottom line is that an occasional energy drink is fine for most people, but do the math and avoid overindulging.
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