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Heart's strain rate may be raised by energy drinks

Caffeine energy drinks “intensify heart contractions,” BBC News reports.

The news is based on a small study of 18 healthy adults who had heart scans taken before and one hour after drinking an energy drink containing caffeine and taurine (a chemical said to have stimulant properties).

The study’s preliminary results were presented at the annual meeting of the Radiological Society of North America.

From an abstract of the presentation and a press release, it seems the researchers found that “strain rate”, a measure of the speed of heart muscle contraction, was significantly increased after the energy drink was consumed. However, the researchers found no changes to volume of blood pumped, pulse rate or blood pressure an hour after the energy drink.

Overall, this study raises an important issue over the effects energy drinks could have on the heart. However, many questions remain unanswered following this small study that has not yet been published in a peer-reviewed journal. Further research on more people is needed.

The effect on people with heart conditions has not yet been studied, but until then, if you do have a history of heart problems you may want to err on the side of caution and limit your consumption of caffeine-containing energy drinks.

Where did the story come from?

This was a conference abstract of a study presented at a meeting of the Radiological Society of North America. One of the researchers was a consultant for Medtronic, Inc, a US company which manufactures medical equipment. No other potential conflicts of interest were reported.

BBC News reporting of the research was accurate.

What kind of research was this?

This study has not yet been published in a peer reviewed journal, and only limited study information is available. As such it is not possible to fully assess the methods or quality of this study.

The researchers describe that energy drinks usually contain a large amount of caffeine, taurine, and sugar, and currently there is little or no regulation over their sale. There are said to be concerns about adverse effects in adolescents and young adults, particularly on heart function.

This was an experimental study in which 18 healthy adults had their heart function assessed in an MRI scanner before and after drinking an energy drink.

What did the research involve?

The abstract describes that the study included 15 healthy men and three healthy women, with an average age of 27.5 years. They were investigated using cardiac magnetic resonance imaging (CMR), which shows the structure of the heart and how it is functioning.

CMR was performed on a whole-body scanner before, and one hour after, drinking an energy drink containing taurine (400mg/100ml) and caffeine (32mg/100ml). Each individual was given a volume to drink calculated as 168ml/m2 of their body surface area.

The researchers looked at how the left ventricle (the heart chamber that pumps oxygenated blood out of the heart and to the rest of the body) was functioning by measuring its peak strain and peak strain rate during heart contraction and dilation (measures of contraction). They also recorded heart rate and blood pressure.

What were the basic results?

The researchers found that peak strain of the heart, and peak strain rate during heart contraction, the speed at which the muscles contract, were significantly increased one hour after consumption of the energy drink. However, the health implications, if any, of the difference are not reported. There was no significant difference in peak strain rate during heart dilation.

The energy drink also had no significant effect on the amount of blood being ejected from the left ventricle, heart rate or blood pressure.

How did the researchers interpret the results?

The researchers say that drinking an energy drink has a short-term impact on heart contraction. They say that further studies are needed to look at the impact of drinking energy drinks in the long term, and to see whether the drinks could have a detrimental effect on people with heart disease.

Conclusion

This study has not yet been published in a peer reviewed journal, and only limited study information is available. As such it is not possible to fully assess the methods or quality of this study.

The study appears to demonstrate that 18 healthy adults who consumed energy drinks had significantly increased strain rate of heart contraction one hour later. There was no overall change to the volume of blood the heart was pumping out, pulse rate or blood pressure.

In an accompanying press release one of the associated researchers Dr Jonas Dörner, of the University of Bonn, Germany, says: “There are concerns about the products’ potential adverse side effects on heart function, especially in adolescents and young adults, but there is little or no regulation of energy drink sales.”

He continues: “Usually energy drinks contain taurine and caffeine as their main pharmacological ingredients. The amount of caffeine is up to three times higher than in other caffeinated beverages like coffee or cola. There are many side effects known to be associated with a high intake of caffeine, including rapid heart rate, palpitations, rise in blood pressure and, in the most severe cases, seizures or sudden death.”

Somewhat surprisingly, given the popularity of energy drinks, this has been one of the first studies to look at effects on the heart.

One of the chief limitations of this study is its small sample of only 18 people, most of whom were men. It is not known how these men were selected, or whether the same significant effects on contractility would be observed if a much larger or different sample had been tested.

Other limitations include, as Dr Dörner acknowledges, not knowing how long this measured increase in contractility lasts, whether it has any effect on normal activities, and whether it has any effect on ability to do exercise.

It’s also unclear what effects could occur if energy drinks were used in combination with alcohol or other stimulants (energy drinks are popular with clubbers, and as hangover cures, so this is an important consideration).

This presentation raises more questions than it answers: it is unclear what the increase in heart contraction would have in a larger, more diverse population and at differing levels of consumption. Importantly, this presentation can’t tell us about the effects of energy drinks on people with heart conditions.

So, this study cannot prove that energy drinks are bad for the heart, but if you do have a history of heart problems you may, as a general principle, want to limit your caffeine consumption.

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