The researchers found that Japanese adults drinking five or more cups of green tea daily were 16 per cent less likely to die from a range of illnesses, and particularly heart disease, than those only drinking one cup per day.
The healthy effect of green tea on women appeared to be double what it was for men.
The study, published in the Journal of the American Medical Association, assessed more than 40,000 people aged between 40 and 79 for up to 11 years.
It improves the case for more clinical trials to define the potential health benefits of green tea.
"Clinical trials are ultimately necessary to confirm the protective effect of green tea on mortality," said the researchers, led by Shinichi Kuriyama of Tohoku University.
It was unclear how significant other dietary and lifestyle factors may have been in the Japanese study's findings.
Around 80 per cent of people in north-eastern Japan, where the study was done, regularly drink at least three cups of green tea every day. Heart disease rates are lower in Japan than in several developed nations in Western Europe, but the Japanese diet is considered healthier overall.
Shinichi Kuriyama told BeverageDaily.com the researchers had considered and controlled many lifestyle factors, including smoking, exercise, diet and the health history of those involved in the study.
Japanese people have the longest life expectancy in the world, but there have been few specific studies on possible dietary reasons for this.
"Although factors other than diet may also contribute, green tea, a harmless drink with no calorific value, might provide a clue to clarifying the reason for Japanese longevity among dietary factors," said Kuriyama.
A recent review of tea's health benefits, published in the European Journal of Clinical Nutrition, found "clear evidence" that three or more cups of tea per day reduced heart disease risk - largely due to tea's antioxidant content.
The link between tea and lower cancer risk remained unclear, the review added.
The Japanese study said it found "no significant association between green tea consumption and death from cancer". It also added that black tea, more commonly drunk in the UK, did not appear to improve consumers' chances of staying alive.
Kuriyama said the researchers on the Japanese study believed their results were more conclusive than several previous studies because they had assessed more people.