The Mediterranean diet has already been credited with increasing life expectancy levels in southern Europe. Now research has revealed that it may also contribute to the health of the unborn child in the womb.

According to the first comprehensive estimate of the global burden of birth defects, France has the lowest incidence rate in the world, and researchers believe the Mediterranean diet could be the reason.

A high daily intake of leafy vegetables, high in folic acid and a staple of most Mediterranean cooking regimes, ensures that France, Italy and Spain fare significantly better than other nations in avoiding defects such as congenital heart problems and spina bifida. The French rate of 39.7 babies born with birth defects per 1,000 live births is less than half that in the Sudan, which has the highest rate in the world, at 82 per 1,000 live births. The UK ranks ninth in the table, behind Spain and Italy, with 43.8 affected babies per 1,000 live births.

Almost 250,000 babies are born with inherited birth defects each year in Europe, but the toll could be reduced if their mothers ate more fruit and vegetables as in Mediterranean countries, researchers say.

The Global Report on Birth Defects published by the American charity March of Dimes says eight million affected babies are born each year, of whom 3.3 million die before they reach the age of five, a greater toll than from Aids, malaria and tuberculosis combined.

A further 3.2 million of those who survive may be mentally and physically disabled for life. The total does not include the one million babies born with defects caused by exposure to environmental or chemical agents in the womb, including infections, bringing the total of affected babies to nine million, the researchers say.

The problem has been ignored by governments despite the availability of simple public health measures which could reduce the toll, the report says. Jennifer Howse, president of the March of Dimes, said: "Our report identifies for the first time the severe and previously hidden global toll of birth defects. This is a serious, vastly under-appreciated and under-funded public health problem."

The commonest inherited birth defects are congenital heart problems and neural tube defects such as spina bifida. Rates are up to twice as high in the poorest countries compared with the richest.

Professor Bernadette Modell of the Royal Free and University College Medical School said boosting folic acid levels in pregnant women was the single most important element to prevent defects.

Folic acid is contained in green leafy vegetables and prevents spina bifida. In the UK, pregnant women are prescribed folic acid supplements, but only half take them. "Fortifying flour with folic acid globally should be a priority," Professor Modell said. "They have done it in North America and they are seeing a fall in defects."

The incidence of birth defects including Down syndrome, spina bifida and congenital heart problems is up to 16 per cent lower in southern Europe than northern Europe.

Professor Modell said: "They are highest in the north and east and lowest in France, Italy and Spain. The Mediterranean diet doesn't just prevent heart disease - it seems to have an effect on birth defects too. It is probably the effect of folic acid, but it is quite possible there are multiple vitamin effects."

In the UK birth defects have fallen by 70 per cent over the past 40 years as a result of better screening and prevention. About 30,000 affected babies are born in Britain each year.