The meta-analysis took into account data from 95 studies which analysed fruit and vegetable intake for a total of two million people, covering up to 43,000 cases of heart disease, 47,000 cases of stroke, 81,000 cases of cardiovascular disease, 112,000 cancer cases and 94,000 deaths.
Writing in the International Journal of Epidemiology, the researchers calculated that around 7.8 million premature deaths worldwide could be potentially prevented every year if people ate 10 portions (800 g) of fruit and vegetables a day.
Even when taking into account confounding lifestyle factors such as weight, smoking, physical activity levels and overall diet, fruit and vegetable intake still came out top.
What's in a portion?
A standard 80 g portion of fruit or vegetables is equivalent to one small banana, an apple, pear or a large mandarin.
It could also be three heaped tablespoons of cooked vegetables such as spinach, peas, broccoli or cauliflower.
The researchers went further and looked at associations between consumption of certain vegetables and specific diseases. A high intake of apples and pears, citrus fruit, green leafy vegetables such as spinach, and cruciferous vegetables such as broccoli or cabbage may help prevent
heart disease, stroke, cardiovascular disease and early death.
Meanwhile green vegetables, such as green beans, yellow vegetables, such as peppers and carrots, and cruciferous vegetables may reduce cancer risk.
Several mechanisms could be behind this, according to Dr Dagfinn Aune, lead author of the research from the School of Public Health at Imperial College London.
"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."
It could also be due to glucosinolate compounds in cruciferous vegetables, such as broccoli, that work by activating enzymes associated with cancer prevention, or by stimulating healthy bacteria in the gut.
Unrealistic expectations?
The ten-a-day recommendation doubles the UK government's current healthy eating advice.
Many people following a ‘Western diet’ today eat insufficient amounts of fruit and vegetables. But how much you are told to eat depends on where you live.
According current recommendations set by the World Health Organisation (WHO) and the UK government, fruit and vegetable intake should be at least 400 g/day. For years, the UK's healthy eating advice has centred around the message to eat five pieces of fruit and vegetables a day.
Swedish public health authorities recommend 500 g/day while in Denmark it’s 600 g/day. Norwegians are told to eat between 650 and 750 g/day while the US tells Americans to eat between 640 and 800 g/day.
Given the disparity between current recommendations and the reality, UK public health authorities said they do not intend to change their advice.
Dr Alison Tedstone, chief nutritionist at Public Health England, said: "Whilst consuming more than five portions of fruit and vegetables a day may be desirable, two thirds of adults currently don't consume the recommended minimum of five-a-day.
"Adding pressure to consume more fruit and vegetables creates an unrealistic expectation."
No short cuts
Bad news for the supplements industry; it’s not as simple as encapsulating these benefits in a pill. Aune said: "Most likely it is the whole package of beneficial nutrients you obtain by eating fruits and vegetables that is crucial is health. This is why it is important to eat whole plant foods to get the benefit, instead of taking antioxidant or vitamin supplement, which have not been shown to reduce disease risk."
Source: International Journal of Epidemiology
"Fruit and vegetable intake and the risk of cardiovascular disease, total cancer and all-cause mortality-a systematic review and dose response meta-analysis of prospective studies"
First published online ahead of print February 2017, doi: 10.1093/ije/dyw319
Authors: Dagfinn Aune, Edward Giovannucci, Paolo Boffetta, Lars T. Fadnes, NaNa Keum, Teresa Norat, Darren C. Greenwood, Elio Riboli, Lars J. Vatten and Serena Tonstad