Energy drinks are becoming increasingly popular, and with exciting names like Red Bull, Adrenaline Rush, 5-Hour Energy, and Hype, they promise to give a boost of energy and keep a person alert. But are they safe? More to the point, are they safe to use in tandem with exercise and competitive sports, particularly in younger people?

The term "energy drink" refers to a beverage that contains caffeine in combination with other ingredients such as taurine, guarana, and B vitamins, and claims to provide its consumers with extra energy. Energy drinks were introduced to the public during the mid-1980s in Europe and mid-1990s in the US. The market for the drinks was estimated at $5.4 billion in 2006, according to Packaged Facts, and enjoys an annual growth rate of 55% per year. These beverages are a huge business, and are heavily marketed toward teens and young adults, particularly young men.

There is no clear definition of what an energy drink is, not even from federal regulatory bodies, because "energy drink" is a marketing term coined by the industry1. As a matter of fact, there is so little oversight in the US that, in the fall of 2008, a petition signed by 100 doctors and scientists was submitted to the FDA seeking to require energy drink manufacturers to list the caffeine content on the container, to set a limit on the amount of caffeine and other stimulants allowed in the drinks, and to require warning labels. The FDA has set limits for caffeine levels in soft drinks, such as Coke and Pepsi, at 65 mg for a 12-oz (350-ml) serving. Energy drinks, however, are not subject to these guidelines, and can have significantly higher levels of caffeine.

Every energy drink can contain any number of ingredients, but they are essentially soft drinks with high levels of glucose and different combinations of caffeine, guarana, taurine, B vitamins, and various herbs.

Caffeine is a stimulant used by people all over the world. Because of its widespread use and availability, it is easy to forget that caffeine is a drug, and should be approached as such. Some energy drinks do not list caffeine as an ingredient. Instead, they label their drinks with guarana or yerba mate, naturally caffeine-containing substances, which can contain as much as 40mg of caffeine per gram. Energy drinks can contain between 75-150mg of caffeine per serving. However, each container may hold 1-3 servings, which can result in some drinks having over 450mg of caffeine per bottle, about triple the caffeine content of colas. In comparison, one serving (8 fl oz/235ml) of coffee, tea, or cola contains between 134-240 mg, 48-175 mg, and 22-46 mg of caffeine, respectively.

The amount of caffeine in a single energy drink is probably not harmful for most adults. A recent literature review determined that consumption of ? 400 mg of caffeine daily by healthy adults is not associated with adverse effects. Adverse effects of too much caffeine may include nervousness, irritability, sleeplessness, increased urination, abnormal heart rhythms (arrhythmia), decreased bone density, and stomach upset. A single energy drink each day is probably not harmful for adults; however, more than one bottle or an energy drink in combination with other caffeinated beverages, such as coffee or tea, can easily increase a person's caffeine intake to unhealthy levels. Since the effects of high levels of caffeine on people that participate in sports haven't been studied, you should avoid drinking too much caffeine when you're exercising. More about this later.

Although probably not dangerous for adults, the levels of caffeine in energy drinks certainly exceed the safe recommendations for children. The American Academy of Pediatrics suggests no more than 45 mg/day for children 4-6 years, 62.5 mg/day for 7-9 years, and 85 mg/day for children 10-12 years. Adolescents should limit caffeine consumption as well, and consume less than 100 mg daily, as higher levels have been associated with potential negative long term health consequences, most notably, elevated blood pressure. Pregnant and breastfeeding women should consume less than 300mg per day, as higher amounts of caffeine can have negative impact on developing fetuses and infants.

Taurine is an amino acid that our body is able to produce naturally and that can be consumed in meat and dairy products. Some energy drinks claim that taurine makes you more alert, lowers the risk of diabetes and epilepsy, and can treat high blood pressure. Although there is no sufficient clinical evidence to show that taurine is effective in treating diabetes or epilepsy, it may lower blood pressure - but more research is required to confirm this. Many energy drinks contain as much as 1 gram of taurine per 8-oz (225-ml) serving; the safety of such large doses is not known.

B vitamins are an important part of a healthy diet and are essential for breaking down carbohydrates into glucose, which provides us energy, and for breaking down fats and proteins. B vitamins are water-soluble, meaning that when more B vitamins are consumed than the body needs, small amounts are stored in body tissue, but most of the excess is lost in the urine. Common names for B vitamins are folate, niacin, riboflavin, cyanocobalamin, and pyridoxine hydrochloride.

Some energy drinks contain as much as 2000%-8000% of the Recommended Daily Allowance of some B vitamins. Although most will be lost in the urine, these extremely high levels of certain B vitamins could pose major health problems. Excessive B-6 (pyridoxine) may cause nerve damage when habitually consumed. High doses of niacin may pose problems for the athlete, as well: At high doses, it may shift metabolism to burn more carbohydrate and less free fatty acids, which could hinder endurance performance. High levels of folate can hide a B-12 (cyanocobalamin) deficiency. It is best not to consume extremely high levels of B vitamins.

Hope Barkoukis, chairwoman of the Sports, Cardiovascular, and Wellness Nutritionists group of the American Dietetic Association says, "It's brilliant marketing... but it doesn't have any [scientific] basis." There is no evidence to suggest that B vitamins increase energy levels via supplementation. They also do not appear to promote athletic performance. The fact is, most people consume more than their daily B vitamin requirement in their normal diet.

Many energy drinks contain herbs, such as gingko biloba, ginseng, and others. These popular herbs boast many health benefit claims; however, there is very little scientific evidence to support their use. Ginseng, for example, is touted as a way to speed illness recovery; to improve mental, physical, and sexual performance; to control blood glucose; and to lower blood pressure. However, there is no scientific evidence to support any of these assertions. Most of these herbs have not been shown to improve athletic or mental performance. And although the level of herbs added to most energy drinks is very low - and probably not normally dangerous - these substances can cause adverse interactions with some medications.

Glucuronlactone is an ingredient in some energy drinks that attracts more attention than others. Energy drinks claim glucuronlactone detoxifies the body and protects against cancer! But, there is no scientific evidence to support these claims.

Children and teenagers in particular can confuse the difference between energy drinks and sports drinks, but they are not sports drinks at all: These beverages' effects when combined with exercise are not well-studied, and they have limited federal regulation. Energy drinks are marketed for their stimulant effect on the mind and the body. They are essentially soft drinks with high levels of sugar, caffeine, taurine, ginseng and B vitamins.

Many athletes, particularly adolescents, use caffeine before and during competition to help boost physical performance. Energy drinks are heavily marketed toward young men as performance enhancers, with ads and promotions often linked to endurance athletics and extreme sports. Many of these drinks claim to have the ability to increase endurance, reaction time, and concentration due to exotic herbs and other ingredients; but in reality, any physical or mental effects most likely come from caffeine!

Research has found that consumption of moderate levels of caffeine prior to and during heavy exercise is safe and effective12. But the safety of consuming caffeine in combination with the herbal supplements found in many energy drinks, particularly prior to or during exercise, has yet to be established. Also, the amount of caffeine tested in much of the scientific research is far lower than that of some energy drinks: Very high levels of caffeine intake greatly increase the risks of negative side effects, but there is little evidence for any added athletic benefits.

There have been limited studies on the effect of hydration and electrolytes with respect to caffeine and energy drinks. The results of this research are mixed, with little evidence to support that the added herbs and other substances in energy drinks result in dehydration. However, caffeine has a diuretic effect (body loses water through increased urination). The addition of moderate levels of caffeine to a standard sports drink does not have a negative impact on hydration and performance. However, the effects on hydration of much larger quantities of caffeine found in energy drinks are not known.

Although low levels of caffeine do not seem to have a large effect on hydration and electrolyte balance during exercise, the high level of sugar in many energy drinks may have a negative impact. The high concentration of glucose in many energy drinks results in slower absorption of fluids in the gut, and may lead to gastrointestinal distress and dehydration. Sports drinks are specially formulated to contain the appropriate balance of glucose and electrolytes for easy absorption, thereby providing fuel to working muscles, as well as water and electrolytes to maintain optimal hydration. Most energy drinks have not been designed this way, and statements from certain energy drinks companies claim that their product is "not a fluid replacement drink."

The bottom line is that there are still many unknowns in the relationship between the ingredients in energy drinks and athletics. Until the safety of this practice can be established, consumption of energy drinks prior to and during exercise by individuals is not recommended, especially for young people whose bodies are still growing and developing.

The fact that the FDA or any other agency does not closely regulate energy drinks has, in part, resulted in their aggressive marketing as a psychoactive, performance-enhancing stimulant. Along with the fact that there are highly variable levels of caffeine from one drink to another and its levels are not listed on the can may increase the risk of negative health effects, particularly for youths who may be caffeine-naïve. "You can pick up a can and drink it and get 50 milligrams, which is the amount in a Mountain Dew, or pick one up and get 500 milligrams, and that's enough to put someone who hasn't built up a tolerance to caffeine into caffeine intoxication," says Roland Griffiths, a neuroscientist at Johns Hopkins School of Medicine in Baltimore.

Caffeine intoxication is generally mild: Adverse effects, such as nervousness, anxiety, restlessness, insomnia, nausea, vomiting, tremors, and rapid heart rate, begin to occur at low doses, and often prevent further caffeine intake. People with cardiovascular disease, high blood pressure, improper blood vessel function, or seizure disorders are at increased risk of the negative health effects of energy drinks. A 2007 article described patients experiencing seizures after heavy consumption of energy drinks. The research is not strong enough to make a definitive recommendation, but it is strong enough to be a caution to people with certain risk factors. It is important to remember that caffeine is an addictive drug, and as little as 100mg daily can result in dependence. Fatigue, depression, difficulty concentrating, or headaches are some withdrawal symptoms for people who do not consume their daily caffeine drink - real indications of dependence.

Caffeine is a powerful stimulant and can boost athletic performance; however, energy drinks are not optimal for proper hydration, carbohydrate delivery, or the appropriate amount of caffeine for athletics performance. There is very little known about the various other substances found in many energy drinks, especially in such high concentrations. Energy drinks consumption should be limited to adults, used with caution, and perhaps only consumed on certain occasions where a true caffeine boost is needed - but not during athletics!

• Not regulated by the FDA or other government regulatory bodies
• Highly variable levels of caffeine depending on the drink and brand
• The effect of high levels of caffeine found in energy drinks does not result in greater athletic benefits
• Caffeine levels that may result in caffeine intoxication
• Potentially dangerous levels of B vitamins
• Various ingredients with minimal scientific evidence to support their safety and use
• Not designed as a fluid replacement beverage; may even delay glucose absorption and result in dehydration
• Not designed to replenish electrolytes lost in sweat
• May complicate or induce preexisting medical conditions
• There are many unknowns related to energy drink consumption and their effect on athletic performance