Those who despaired of ever being able to eat seven portions of fruit and vegetables a day, as suggested by a team of scientists earlier this year, can probably relax. A new and even bigger study carried out by Chinese and American researchers says five will do.

The two teams are in agreement on the main issue: eating more fruit and vegetables than most of us currently do is a very good thing. The evidence suggests that it lowers the risk of dying from heart disease or cancer.

But the more difficult issue is to figure out how much is enough in order to formulate guidelines for people who may not particularly enjoy eating their greens, as well as those who complain they are expensive.

In April scientists at University College London analysed the eating habits of 65,000 people who had responded to the Health Survey for England over eight years. They found that the more fruit and vegetables people ate, the better, and that vegetables had a greater protective effect than fruit.

Eating at least seven portions of fresh fruit and vegetables a day was associated with a 25% lower risk of cancer and 31% lower risk of heart disease or stroke. Their findings were published in the Journal of Epidemiology and Community Health, part of the BMJ (British Medical Journal) group.

In the latest study, published in the BMJ itself, researchers pulled together the results from 16 studies to get an overview, involving a total of 833,234 participants, of whom 56,423 had died. The studies were designed differently, and were of varying quality, but the researchers from Chinese and US universities including the Harvard School of Public Health in Boston were able to allow for that in their analysis.

They found that the average risk of death from all causes was reduced by 5% for each additional daily serving of fruit and vegetables, and the specific risk of cardiovascular death – from heart disease or stroke – was reduced by 4% for each additional daily serving of fruit and vegetables. But the risks did not drop any further for those people who ate more than five portions a day.

They also found that eating more fruit and vegetables did not particularly protect people from cancer. There are other risk factors which may be more important, they suggest, such as obesity, physical inactivity, smoking and drinking. It is not clear whether eating more fruit and vegetables might lower the risk of some specific types of cancer, and more studies are needed, they say.

The UCL team was not dismayed by the results, however. Dr Jenny Mindell said the evidence for seven a day was not as strong as for five a day, but they were happy with their findings from the English sample. "People who ate more fruit and vegetables had a lower mortality and we did indeed find the lowest mortality among people who ate seven or more portions of fruit and vegetables, although the precision around that means it may not be lower than among those eating five or six portions.

"Also, in our study, people who ate more vegetables had a lower mortality than people who ate a similar amount of fruit, but that wasn't seen in this meta-analysis. We don't yet know whether vegetables are more protective than fruit or whether it's to do with the rest of their diet or if people who eat more vegetables are different from people who eat more fruit. And we don't know whether the type of fruit or vegetables, or other aspects of diet, in these different populations affects the results.

"But as our study was based on the general population in England, we can be confident that we should advise people to stick to the current guidelines of eating at least five portions a day of fruit and vegetables."