If you reach for a Red Bull when you need a jolt, it just might give you a bigger one than you bargained for. Super-caffeinated energy drinks could cause havoc with your cardiovascular system and produce symptoms that are serious enough to send you to the emergency room (ER).

Background: Athletes and students made energy drinks popular, but recently they’ve become the beverage of choice for moms and middle-aged folks looking for a power boost. With their blend of caffeine and other stimulants, energy drinks seem like a natural way to increase your focus and stamina. But along with their rise in sales has come a corresponding increase in ER visits, especially in older people.

What’s behind that rise? After all, caffeine is generally thought to be safe up to a dose of 400 mg, the equivalent of four cups of brewed coffee. Researchers speculate that these other “natural” ingredients in energy drinks might exacerbate the stimulating effects of caffeine, which could be uniquely bad for your cardiovascular health.

Study: Researchers recruited healthy men and women between the ages of 18 and 40 from a US Air Force base. The study’s subjects drank a 32-ounce energy drink, which contained 320 mg of caffeine. But it also contained the usual blend of other ingredients often found in energy drinks, including sugar…

  • Guarana, a stimulant compound derived from the seeds of a Brazilian fruit
  • B vitamins, which help the body convert nutrients into the form of energy that cells can use
  • Taurine, an amino acid that may improve athletic performance
  • Carnitine, derived from an amino acid, that also has been shown to improve athletic performance
  • Panax ginseng, a traditional Chinese medicine often used for fatigue
  • Glucuronolactone, a naturally occurring compound produced by the body that is purported to improve athletic performance and might fight fatigue.

Each of the participants also drank a 32-ounce drink that looked and tasted like a regular energy drink but  contained only the same dose of caffeine. These drinks were given in random order. Some got the energy drink first , some got the placebo drink first­, and then they got the other drink six days later. Even the researchers didn’t know which drink was being served. Then the researchers monitored the subjects’ blood pressure and heart rate, once before they consumed each beverage and then several times over the following 24 hours.

Results: After drinking either drink, the subjects reported a host of negative symptoms, including anxiety, dizziness, palpitations and shortness of breath.

But the energy drinks produced two unique—and worrisome—symptoms. One was a prolonged blood pressure spike. While the caffeinated beverage caused blood pressure to go up, that spike lasted for only an hour. The energy drink produced a rise in systolic blood pressure that stayed elevated for six hours. That’s a big difference.

The other symptom was a prolonged QT interval that lasted for two hours. Cardiologists use QT intervals to measure the heart’s electrical system. An increase in the QT interval is a sign that the heart isn’t beating normally. Doctors consider it a risk factor for arrhythmias (abnormal or irregular heartbeats) and sudden cardiac death.

Bottom line: If you need an afternoon boost, it’s safer to down a mug or two of strong coffee than an energy drink. While this study looked at younger, presumably fit military men, the message is particularly relevant to middle-aged and older people. Cardiologists warn that the risk of developing an irregular heartbeat increases with age. The researchers note that energy drinks are particularly risky if you have a magnesium or potassium deficiency (which can affect heart rhythm)…take heart medications to control arrhythmia…take certain diuretics to control blood pressure…or are obese. And never, ever mix these beverages with alcohol—even if you’re in great shape. The cumulative effect, other research has found, may just be too much for the heart.