London - Just two glasses of diet drink a day increases the risk of an early death, a World Health Organisation study has shown.
Research involving more than 450 000 adults in ten countries found that daily consumption of all types of soft drinks was linked with a higher chance of dying young.
But the rates for those drinking artificially-sweetened beverages were significantly higher than those consuming full sugar versions.
The scientists, from the WHO International Agency for Research on Cancer in Lyon, said it would be ‘prudent’ to cut out all soft drinks and have water instead.
The research is the largest study to examine links between soft drink consumption and mortality.
Previous smaller studies have suggested a link, but have not found such dramatic differences. The new research, published in the JAMA Internal Medicine journal, found those who consumed two or more 250ml glasses of diet drink a day had a 26 percent increased risk of dying within the next 16 years.
And deaths from cardiovascular disease went up 52 percent.
For those who had two or more sugary soft drinks a day, the risk of death in the same period was raised by just eight percent. And the scientists warned that taxing sugary drinks could boost diet drink uptake.
Speaking at the European Society of Cardiology in Paris, the group said people should "eliminate" soft drinks from their diet.
Study leader Dr Neil Murphy said: "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."
Dr Murphy said it was "unclear" exactly why this was, but pointed to previous studies which suggested the artificial sweeteners in diet drinks "may induce glucose intolerance" and trigger high blood insulin levels.
Additional studies are now needed to examine the long term health consequences of specific artificial sweeteners that are commonly used in soft drinks, such as aspartame and acesulfame potassium, he said.
The new study also found the link between diet drinks and death rates persisted among those of a healthy weight.
Stroke specialist Professor Mitchell Elkind, from the American Heart Association, speaking in Paris, said: "It’s a very big study and includes many countries. Water is the safest thing. Tea and coffee are okay. But minimise or completely eliminate processed beverages."