Just two diet drinks a day raises the risk of dying young by a quarter, a major study has revealed.

Diet Coke and Pepsi Max drinkers see their chances of being killed by a heart attack or stroke rocket by more than half, compared to those who avoid diet drinks altogether.

Experts said the “important” European findings, involving more than 450,000 people in the study, were “concerning”.

The World Health Organisation research found the dangers of consuming artificially sweetened soda were up to three times greater than regular sugary drinks.

It suggests switching to sugar-free products, like Diet Pepsi or Sprite Zero, could be equally bad for health, if not worse.

The study was carried out by the International Agency for Research on Cancer in France, which is a part of the WHO.

“The striking observation in our study was that we found positive associations for both sugar-sweetened and artificially-sweetened soft drinks with risk of all-cause deaths. It would probably be prudent to limit consumption of all soft drinks and replace with a healthier alternative, such as water.” said Lead researcher Dr Neil Murphy.

The findings, published in JAMA Internal Medicine, coincide with the largest gathering on heart experts in the world.

Speaking from the European Society of Cardiology congress in Paris, Professor Mitchell Elkind, incoming president of the American Heart Association urged people to give up soft drinks.

“This study is important. There are concerns about both sugar sweetened beverages and so-called diet beverages. There may be a direct impact [of diet drinks] – and other studies have suggested biological mechanisms may include an impact on insulin signalling in the liver. The take home message is drink water – certainly avoid sugar sweetened beverages and be cautious about artificially sweetened beverages.” Elkind stated.

Previous research suggests sweeteners may affect blood vessel health, dementia risk and also trigger weight gain.

One theory is that it affects the body’s sugar levels and key hormones, such as insulin.

Others claim unhealthy adults are more likely to turn to diet drinks, which contribute to the findings.

“Soft drinks are safe to consume as part of a balanced diet.” said Gavin Partington, Director General at British Soft Drinks Association.