In an unpublished study, German researchers found healthy adults showed a significant increase in heart contraction rates after consuming high-caffeine, high-taurine energy drinks. (Via WRAL)

Eighteen people underwent cardiac MRIs before and one hour after downing an energy drink. According to the Daily Mail, the results indicated an increase in activity in the left ventricle of the heart, which helps pump blood to the rest of the body.

The study's author, Dr. Jonas Droner, said energy drinks can contain up to three times more caffeine than coffee or soda, and cautioned children and people with irregular heartbeats to avoid the drinks altogether. (Via WCSH)

But the claim about caffeine levels opened the authors up to a few critics. A writer for Forbes points out: "The drinks that Dorner and his colleagues gave their 18 subjects contained 32 milligrams of caffeine per 100 milliliters, compared to 76 milligrams per 100 milliliters for Starbucks coffee."

And the American Beverage Association confirmed that in a statement, saying, "Most mainstream energy drinks contain only about half the caffeine of a similar size cup of coffeehouse coffee."

But regardless of whether caffeine is the harmful factor here, the Substance Abuse and Mental Health Services Administration reported the number of emergency room visits linked to energy drinks nearly doubled from 2007 to 2011.

"So what might be going on to send someone to the ER?"

"Blood pressure goes up, heart rate goes up, and then they'll start to feel the effects: heart racing, heart skipping, panic attack symptoms, irregular heart rhythms." (Via ABC)

Hospital visits aside, the German researchers say it's still not known what the long-term effects of energy drinks are, and they plan to carry out further studies.

- See more at newsy.com.