Seven portions every day could have a more protective effect, experts said.
Health experts recommends 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.
But a 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%.
Eating this many portions can also reduce a person's risk of dying of heart disease by 31%, the authors said. The researchers from University College London examined the eating habits of 65,000 people in England between 2001 and 2013.
They found that seven or more helpings a day can reduce a person's overall risk of death by 42% when compared to people who manage just one whole portion every day.
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 increase the risk of death, and no significant benefit of fruit juice was noted.