Medical professionals concerned by energy-drink buzz

Photo / Herald on Sunday

One energy drink can raise a person's heart rate by 24 beats a minute, causing dizziness and shaking.

The Herald on Sunday tested the effects of popular drinks high in caffeine and sugar on five Vodafone employees aged between 22 and 33 using a Polar heart rate monitor.

We recorded their resting heart rates for a minute and measured it for the same period after they had finished their drinks. Each drank a different product.

Cathy Willis, 27, certainly felt the effects of 120ml of XShot within minutes.

Her resting rate was 74 beats a minute but shot up to 98.

The label warns XShot may increase heart rate and states there is 300mg of caffeine per bottle - the equivalent of three cups of coffee.

"I do feel a little more shaky and jittering," she said.

Her colleague James Barnett, 22, was surprised by the effect of regular Coca-Cola. He started with a resting pulse of 92 beats a minute, but after 300ml of Coke it leaped to 108.

Energy drink lover Stephanie Kunze had a resting pulse of 81, but after a can of V it rose to 86 beats a minute.

Other testers had a decreased heart rate.

Alexis Sinden, 26, said she felt more energised after a 355ml bottle of Mother containing 114mg of caffeine.

But her heart rate peaked at 90 beats a minute after she drank it, compared to 93 before. Sinden said drinking two or three coffees a day may have increased her tolerance to caffeine.

Matt East also experienced a drop in heart rate, despite drinking his first Red Bull in years. His resting pulse was 105 beats a minute but he dropped to 99.

National Heart Foundation medical director Professor Norman Sharpe said the effects on energy drinks on heart rate varied.

He was concerned the products are marketed towards young people.

"They are marketed very aggressively, young people are drinking them in quite big amounts."

Heart specialist Dr Rob Doughty said energy drinks were best drunk in moderation.

"If you're feeling shaky and jittery with it, it's not a good thing."

Drink if you dare

* Auckland mum Brooke Robertson shrank from 105kg to 60kg by drinking 10 to 14 cans of Red Bull a day.

* Green MP Sue Kedgley had a complaint against Demon energy drink upheld by the Advertising Standards Authority in February.

* The maximum level of caffeine allowed in energy drinks is 320mg per litre. Demon Energy Shot contained 3333mg of caffeine a litre.