The study, by Imperial College London, calculated such eating habits could prevent 7.8 million premature deaths each year.
The team also identified specific fruit and veg that reduced the risk of cancer and heart disease.
The analysis showed even small amounts had a health boon, but more is even better.
A portion counts as 80g (3oz) of fruit or veg - the equivalent of a small banana, a pear or three heaped tablespoons of spinach or peas.
What counts as five-a-day?
The conclusions were made by pooling data on 95 separate studies, involving two million people's eating habits.
Lower risks of cancer were linked to eating:
- green veg (eg spinach)
- yellow veg (eg peppers)
- cruciferous vegetables (eg cauliflower).
Lower risks of heart disease and strokes were linked to eating:
- citrus fruits
- green leafy vegetables (eg lettuce)
- cruciferous veg
The results, published in the International Journal of Epidemiology, also assessed the risk of dying before your time.
Compared with eating no fruit or veg a day, it showed:
- 200g cut the risk of cardiovascular disease by 13% while 800g cut the risk by 28%
- 200g cut the risk of cancer by 4%, while 800g cut the risk by 13%
- 200g cut the risk of a premature death by 15%, while 800g cut the risk by 31%
The researchers do not know if eating even more fruit and veg would have even greater health benefits as there is little evidence out there to review.
Dr Dagfinn Aune, one of the researchers, said: "Fruit and vegetables have been shown to reduce cholesterol levels, blood pressure, and to boost the health of our blood vessels and immune system.
"This may be due to the complex network of nutrients they hold.
"For instance, they contain many antioxidants, which may reduce DNA damage and lead to a reduction in cancer risk."
However, many people struggle to even eat the five a day (400g) recommended by the World Health Organization.
In the UK, only about one in three people eats enough.
Dr Aune said the findings did not mean the five-a-day message needed to change.
He told the BBC: "There are many different considerations if changing policy, it's not just the health effects - is it feasible?
"But our findings are quite clear in that they do support five a day, but there are even some further benefits for higher intakes."
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Dr Alison Tedstone, chief nutritionist at Public Health England, said: "The five-a-day target is the foundation of a healthy balanced diet and is an achievable way to help prevent a number of diseases.
"Whilst consuming more than five portions of fruit and vegetables a day may be desirable... adding pressure to consume more fruit and vegetables creates an unrealistic expectation."
Not all of the 95 studies that were analysed fully accounted for other aspects of lifestyle, such as exercise levels, that could also play a role in prolonging lives.
However, Dr Aune said the conclusions were "quite robust"