In a study of 30 university students aged 20-24, Australian researchers found that drinking just one 250-mL sugar-free can of Red Bull increased blood-platelet 'stickiness', raising the risk of blood clots (Heart Lung Circ, 2008; 17 [suppl 3]: S23-4).
As reported by The Australian news-paper, lead researcher Scott Willough-by said the results were alarming: "One hour after they drank Red Bull, [their cardiovascular systems] were no longer normal. They were abnor-mal like we would expect in a patient with cardiovascular disease." He advised that anyone with a historyof heart disease should think twice before consuming the caffeinated energy drink as it could have poten-tially deadly consequences.
But this isn't the first time that Red Bull-and other drinks like it-have been linked with serious adverse effects. Last year, a small US study found that energy drinks raised heart rate and blood pressure (BP) in healthy volunteers. Within four hours of drinking two 250-mL cans of the stuff-containing 80 mg of caffeine and 1000 mg of taurine-heart rates went up by 5 to 7 beats/minute, while systolic BP rose by 10 mmHg. Clearly, patients with high BP or heart disease should avoid these drinks (Circulation, 2007; 116: II_831).
But even more serious adverse events can occur. A report on energy drinks by the German Federal Institute for Risk Assessment (BfR) lists heart dysrhythmias, seizures, kidney failure and fatalities after drinking energy drinks (www.bfr.bund. de/cm/245/new_human_data_on_ the_assessment_of_energy_drinks.
pdf). One healthy 25-year-old man, for instance, suffered "generalized cere-bral seizures" on two occasions after consuming energy drinks on an empty stomach. He had never had symptoms of this kind before, nor did they recur after six months' of abstinence from these drinks.
The BfR also pointed out that data from the National Poisons Information Centre in Ireland (NPIC) report 17 cases during 1999-2005, including two deaths due to the consumption of energy drinks. In these cases, the symptoms observed were confusion, tachycardia and seizures.
Like drinking coffee?
The side-effects associated with energy drinks are usually attributed to their high caffeine content, which can range from 80 mg up to 300 mg (J Am Pharm Assoc (2003), 2008; 48: e55-63). However, energy-drink enthusiasts claim that 'mainstream' drinks like Red Bull only contain about the same amount of caffeine as a cup of coffee.
Nevertheless, unlike hot cups of coffee which are sipped, energy drinks are served cold and can be consumed in larger amounts and more quickly, too. This means the body is subjected to a rapid increase or 'rush' of caffeine effects that doesn't come with coffee.
Also, other stimulants such as guarana and taurine are often added to the brew that enhance the effects of caffeine. Guarana is chemically similar to caffeine and has the same stimulant effects. As Ireland's Stimu-lant Drinks Committee notes, 1 g of guarana contains as much caffeine as a medium-strength cup of coffee (40 mg) (see www.safefoodonline.com/
Although taurine doesn't contain caffeine, like the stimulant, it has a direct effect on heart function and BP (Circulation, 2007; 116: II_831).
Energy drinks also tend to contain high amounts of sugar and/or sweet-eners, which come with their own set of health problems.
The combined effect of these ingredients on the body is as yet not precisely known. However, some countries, such as France and Germany, have already placed tight restrictions on the sale of energy drinks for reasons of safety.
A trend that is increasing in popularity is that of mixing energy drinks with alcohol. Some researchers suggest that, because the caffeine in energy drinks tends to make imbibers feel more alert, those who mix these drinks with alcohol don't realize how drunk they really are and so are more likely to engage in risky behaviour.
Indeed, a recent study found that consuming alcohol mixed with energy drinks is associated with a significantly higher number of alcohol-related consequences among students, such as being taken advantage of sexually, taking advantage of someone sexually, riding with an intoxicated driver, and being physically hurt or injured and requiring medical treatment. Interestingly, the effect was clearly not related to the amount of alcohol consumed (Acad Emerg Med, 2008; 15: 453-60).
More worrying, alcohol mixed with energy drinks have been linked with deaths. According to Germany's Federal Institute for Risk Assessment, alcohol plus caffeine and other stimulants could have a "synergistic effect of possible toxicological relevance compared to the use of isolated