By Erin Hicks

In a new analysis of possible harmful effects of energy drinks on the heart, researchers have found that the drinks may increase blood pressure and disturb your heart’s natural rhythm.

Scientists at the University of the Pacific in Stockton, Calif., analyzed data from seven previously published studies looking at the effect of energy drinks on heart health. The pooled studies included healthy participants 18 to 45 years old.

In their analysis, researchers looked at data on QT interval — the time it takes for the heart's electrical wave to reset before the next beat, as measured using EKG — in 93 people who had just consumed one to three cans of energy drinks. When it's prolonged, QT interval can cause seriously irregular heartbeats or even sudden cardiac death.

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Researchers found the average QT interval was 10 milliseconds longer for those who had consumed energy drinks than for those who had not. Doctors are generally concerned if patients experience 30 added milliseconds in their QT interval from baseline, according to a press release on the study, but any time QT intervals are prolonged it could put you at heart risk, according to Stephen Green, MD, a cardiologist at North Shore University Hospital in Long Island, N.Y.

The researchers also found that systolic blood pressure, the top number in a blood pressure reading, increased an average of 3.5 points in a pool of 132 participants who had consumed energy drinks.

No Regulation for Energy Drinks

Another recent study, published in the Journal of the American Medical Association, reviewed possible risks associated with the levels of caffeine in most energy drinks, and they also reviewed the practice of combining energy drinks with alcohol. Mixing alcohol with energy drinks, they concluded, can lead to risky sexual behavior.

Last October, the U.S. Food and Drug Administration (FDA) received reports of five deaths linked to Monster Energy, a popular energy drink that contains 160 mg of caffeine per 16-ounce can. In November, FDA received reports of 13 deaths over the past four years possibly linked to 5-Hour Energy, an energy shot that contains caffeine and vitamin B12, among other energy boosters.

One issue with energy drinks, said Green, is that they aren’t regulated, so there's not much data on their effects on people with certain medical problems or for those taking other drugs.

For example, Dr. Green said, “We don’t know what’s causing the prolonged QT intervals."

“If you have something you consider a drug, it has to go through a trial and prove safety and efficacy, and then it has to go through the FDA" approval process, said Green, who believes that if energy drinks were a prescription medicine, there would be a warning on the label.

“Herbal foods, vitamins or supplements haven’t really been tested. Whether it’s an energy drink or a supplement or a weight-loss pill, none of these things have really been tested,” he added.

Another issue with energy drinks is that, unlike a cup of coffee, they usually contain other active ingredients that the average user may not be aware of.

“Some of these energy drinks have more than caffeine in them — they are full of other herbs or supplements," said Green. So it's hard for doctors to know when they see possible effects of an energy drink on a patient, which, if any, ingredient in the drink may be causing the issue.

“The problem here with energy drinks is there is no screening. It's just sitting there on the market, and if you’re predisposed to having a prolonged QT for whatever reason, whether you know it or not, it could put you at risk for a serious cardiac event,” he said.

Energy Drinks: Uncertain Risks

Green explained that some people may be at more risk than others when they have energy drinks

“If you’re young, say 22, and don’t have high blood pressure or other medical problems, you may have three double espressos or a Monster energy drink and nothing will probably happen to you,” he said.

"But if you have a history of heart palpitations and drink caffeine or an energy drink, you’ll probably have more heart palpitations because that’s what it does.”

He also warns that just because you've had energy drinks in the past without incident, that doesn't mean you won’t have a problem in the future.

“Say you’re taking cough medicine because you have a cold and then you drink an energy drink. That’s a combination you’ve never tried before with energy drinks, and we don’t know what could happen,” he said.

“It’s like cocaine — you can take it for years and not have a problem, but then take it once and you could have a major problem,” he said.

Bottom line: "If you don’t have any health problems you know of and aren’t on any medication, an energy drink here and there probably won't hurt you. But if you’re on medication, have high blood pressure, or a history of heart palpitations, energy drinks might not be for you,” Green said.

"Energy Drinks: Riskier for Some Hearts More Than Others" originally appeared on Everyday Health.

Also on HuffPost:

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  • Processed Meat

    Hot dogs, bacon, sausage and deli meats -- even lean ones like turkey -- are made with <a href="http://www.health.harvard.edu/healthbeat/avoid-these-foods-for-a-healthier-heart">loads of sodium and preservatives</a>, often including nitrates and nitrites, both of which have been linked to heart problems. "With processing, you lose control over the quality of the ingredients," says <a href="http://drcynthia.com/dr-cynthia/">Cynthia Thaik, M.D.</a>, a Los Angeles-based cardiologist. Processed meats are also <a href="http://www.huffingtonpost.com/david-katz-md/nutrition-advice-the-trut_b_584758.html">higher in saturated fat and lower in protein</a> than any red meat you could prepare yourself, writes director of the Yale Prevention Research Center and HuffPost blogger, David Katz. Not convinced to stay away? Processed meats have also been linked to a <a href="http://www.huffingtonpost.com/2012/01/13/processed-meat-pancreatic-cancer-bacon-sausage_n_1204620.html">higher risk of diabetes <em>and</em> pancreatic cancer</a>.

  • Red Meat

    Yes, the processed picks are <em>worse</em> for your heart, but that doesn't mean you should go wild for steak. Instead, consider it more of a treat than a staple in your diet: It's still high in saturated fat, even when it's unprocessed. "I don't want to suggest that we have to go [completely] plant-based," says Thaik, "but moderation is always the key." If you're not planning on changing your carnivore ways anytime soon, at the very least pick a <a href="http://www.mayoclinic.com/health/cuts-of-beef/MY01387">lean cut of beef</a>, which, according to the USDA, contains less than 10 grams of total fat and 4.5 grams of saturated fat. Or opt for extra-lean, with 5 grams of total fat and less than 2 of saturated fat. Of the 29 cuts that meet these regulations, <a href="http://www.mayoclinic.com/health/cuts-of-beef/MY01387">five are extra-lean</a>, according to the Mayo Clinic, including eye of round roast or steak, sirloin tip side steak, top round roast and steak, bottom round roast and steak and top sirloin steak.

  • Pizza

    That cheesy slice may contain as much as <a href="http://www.realage.com/mens-health-guide/worst-junk-food-for-heart-disease-2">two thirds of your daily recommended limit of saturated fat</a>, according to Real Age, which is found mostly in animal products like beef, pork, butter, cream and milk. The American Heart Association recommends getting no more than <a href="http://www.heart.org/HEARTORG/Conditions/Cholesterol/PreventionTreatmentofHighCholesterol/Know-Your-Fats_UCM_305628_Article.jsp">7 percent of total daily calories from saturated fat</a>. (Based on a 2,000-calories-a-day diet, that totals out to about 15 grams a day of saturated fat). And even though you may think it's "just cheese," many dairy products are actually highly processed, says Thaik. To lighten up, skip extra cheese and top with veggies instead of pepperoni or sausage.

  • Alfredo Sauce

    When you consider that the ingredients in this heavy sauce are <a href="http://allrecipes.com/recipe/alfredo-sauce-2/">butter, cream and cheese</a>, it's easy to see why serving up this pasta dish would pose saturated fat problems -- especially if you're dining out where sauce is ladled over <em>piles</em> of noodles. If you really love an alfredo dish every now and again, ask for the sauce on the side and stick to just a tablespoon or two. If you're making your own at home, try a lightened-up recipe, like <a href="http://recipes.sparkpeople.com/recipe-detail.asp?recipe=163122">this one from SparkPeople</a>, which replaces butter with olive oil, cream with skim milk and cuts down on the amount of cheese.

  • Trans Fats

    These fatty acids are created through processes that make vegetable oils more solid, according to the American Heart Association. They're cheap to produce, are used to make packaged and prepared foods last longer and can be re-used in frying. But <a href="http://www.heart.org/HEARTORG/GettingHealthy/FatsAndOils/Fats101/Trans-Fats_UCM_301120_Article.jsp">trans fats raise LDL or "bad" cholesterol while also lowering HDL or "good" cholesterol</a>, thereby putting your heart at risk. While a number of manufacturers have cut back on trans fat use in light of these health risks, packaged snacks, baked goods and some margarines may still contain it, according to EatingWell. Look for hydrogenated or partially hydrogenated oils on ingredients lists and beware the <a href="http://www.eatingwell.com/nutrition_health/heart_healthy_diet_center/the_worst_and_best_things_to_eat_for_your_heart?page=2">"zero trans fat" labels -- many are hiding .5 grams and rounding down to zero</a>. But considering that the AHA recommends getting <a href="http://www.heart.org/HEARTORG/GettingHealthy/FatsAndOils/Fats101/Trans-Fats_UCM_301120_Article.jsp">no more than 2 grams a day</a>, that adds up, and fast!

  • Fried Foods

    As restaurants use their frying oil over and over again, the <a href="http://www.livescience.com/14781-unhealthy-fried-foods-heart-attacks.html">fat becomes more and more saturated</a>, according to Live Science. And, as mentioned previously, trans fats are often lurking. Even though some restaurants may have cut back in the face of mounting health concerns, a number of joints still fry with solid oils like shortening, says Thaik. However, a 2012 found that <em>how</em> you fry makes a big difference. Among 41,000 Spanish adults, researchers found no link between fried food consumption and heart problems, likely because <a href="http://healthland.time.com/2012/01/25/a-healthier-way-to-eat-fried-foods/">cooking with heart-healthy olive oil is more common</a> than in the U.S, Time.com reported.

  • Soda

    "When we think of heart disease, a lot of people think cholesterol and fat, but we know that sugar, as it relates to obesity and the effect it has on insulin, has a lot to do with the development of artherosclerosis," says Thaik. In fact, drinking one sugary beverage a day leads to a <a href="http://vitals.nbcnews.com/_news/2012/03/12/10656108-soda-drinking-men-at-higher-risk-for-heart-attack">20 percent increase in a man's risk of having a heart attack</a>, according to a 2012 study, <a href="http://thechart.blogs.cnn.com/2012/03/12/a-soda-per-day-may-raise-heart-attack-risk/">even if those empty calories <em>aren't</em> causing weight gain</a>, CNN reported. Soda has previously been linked to <a href="http://www.ncbi.nlm.nih.gov/pubmed/19211821">increased rates of heart disease in women</a>, as well. And diet soda isn't any better. A 2012 study found that a daily diet soda <a href="http://www.nytimes.com/2012/02/28/health/research/diet-soft-drinks-linked-to-risk-of-heart-disease.html">increased risk for stroke, heart attack and death</a>, although the exact cause is not yet fully understood.

  • Fast Food

    There's little on the drive-thru menu that isn't loaded with saturated fat, trans fat, sugar or sodium, making most of your orders recipes for disaster. And the consequences for the heart are nearly immediate. A 2012 study examined the <a href="http://www.huffingtonpost.com/2012/11/27/fast-food-health-arteries-beauty_n_2198725.html">effects of fast food on the arteries after just one meal</a> and found that the ability of the blood vessels to dilate dropped by 24 percent, YouBeauty reported. "Not just fast food but processed food in general has a very high sodium content just by the pure nature of having to do the preservation," says Thaik. Soups and soy sauce are obvious culprits, she says, but saltwater sushi and even bread can be more surprising sources of salt.