The NHS currently advises that every person has five different 80g portions of fruit and vegetables a day.
The suggested intake, based on World Health Organisation guidance, can lower the risk of serious health problems such as heart disease, stroke, type 2 diabetes and obesity, according to NHS Choices.
But a new study suggests that eating seven or more helpings of fruit and veg a day can reduce a person’s risk of dying of cancer by 25 per cent.
Eating this many portions can also reduce a person’s risk of dying of heart disease by 31 per cent, the authors said.
The researchers from University College London (UCL) examined the eating habits of 65,000 people between 2001 and 2013. They found that seven or more helpings a day can reduce a person’s overall risk of death by 42 per cent when compared to people who manage just one portion every day.
People who eat between five and seven a day have a 36 per cent reduced risk of death, those who eat three to five portions have a 29 per cent decreased risk and those who eat one to three helpings of fruit and veg have a 14 per cent reduced risk of death.
The study, published in the Journal of Epidemiology and Community Health, showed that fresh vegetables had the strongest protective effect, followed by salad and then fruit.
The authors also found that canned and frozen fruit appeared to raise the risk of death, instead of lower it. And no benefit from fruit juice was noted.
Dr Oyinlola Oyebode, from UCL’s Department of Epidemiology and Public Health, said: “We all know that eating fruit and vegetables is healthy, but the size of the effect is staggering.
“The clear message here is that the more fruit and vegetables you eat, the less likely you are to die at any age. Vegetables have a larger effect than fruit, but fruit still makes a real difference.
“However, people shouldn’t feel daunted by a big target like seven. Whatever your starting point, it is always worth eating more fruit and vegetables.
“In our study even those eating one to three portions had a significantly lower risk than those eating less than one.”
Dr Oyebode said that most canned fruit contains high sugar levels and cheaper varieties are packed in syrup rather than fruit juice. And she said the negative health impacts of the sugar may well outweigh any benefits.
An accompanying editorial suggests that it may be time for the NHS to rethink the “five-a-day” message – while the authors also suggest it may be time for the NHS to review its guidance on tinned fruit and fruit juice.
But some have questioned the findings of the research, saying that other dietary factors were not taken into account and those who eat large amounts of fruit and vegetables are likely to have a healthy diet in general.
Others also raised concerns about the finding on tinned and frozen fruit, saying that in the survey researchers were not able to distinguish between the two.
Dr Gunter Kuhnle, food scientist from the University of Reading, said: “The researchers were not able to distinguish between the two in their survey, making it impossible to make a distinction in later analysis.
“It’s possible that eating tinned fruits are an indicator of high sugar intake, but it might also be a marker of poverty or lower socio-economic class. As there is no data, it’s simply not possible to speculate.”