By Helen BriggsHealth editor, BBC News website

New research backs the five-a-day target for fruit and vegetables, but suggests eating more may have no added benefits.

An analysis of 16 worldwide studies suggested that for every portion of fruit and vegetables consumed, there was a lower risk of premature death.

But after five portions a day, there was no further impact, researchers report in The BMJ.

There have been calls to up the quota to seven-a-day, to prolong lives.

Current NHS guidance is to eat at least five portions of fruit and vegetables a day. Most people manage about four.

The new analysis looked at 16 studies in the US, Asia and Europe involving more than 833,000 people, of whom about 56,000 died during the follow-up period.

Researchers in the US and China found eating more fruit and vegetables was linked with a lower risk of dying from any cause, particularly from cardiovascular disease.

The average risk of death fell by about 5% for every extra serving of fruit and vegetables, up to five servings a day, but not beyond.

"This analysis provides further evidence that a higher consumption of fruit and vegetables is associated with a lower risk of all-cause mortality, particularly cardiovascular mortality," said the team, led by Prof Frank Hu, of Harvard School of Public Health, in Boston, US.

"There was a threshold around five servings of fruit and vegetables a day, after which the risk of all cause mortality did not reduce further."

Eating even five portions of fruit and vegetables a day is a challenge for many

Seven-a-day?

There have been calls to increase the quota of fruit and vegetables beyond five.

A previous study in England found eating seven or more portions of fruit and vegetables a day was healthier than the minimum five currently recommended and could prolong lives.

But lead researcher Dr Oyinlola Oyebode, of University College London, said both studies showed eating more fruit and veg was associated with lower risk of early death.

"This study suggests not much additional effect over five portions, although there was possibly a greater effect in the groups eating five to seven, and seven plus portions in our study," she told the BBC.

"Most people do not eat five portions of fruit and veg a day, so the message for the public is still to eat more fruit and veg."

Five a day facts