As many as 22 million children throughout the world are overweight, according to the World Heart Federation, which warns that obesity is laying the ground for a 'pandemic' of heart disease.

As the footballer Ronaldo headed a high-profile international campaign to encourage more children to take up sport, doctors said that the increase in prosperity in previously poor countries was creating unprecedented levels of obesity.

Children who would previously have walked or cycled to school now go by bus or car. Fewer children are working on farms, as machinery takes over.

Ronaldo, the Brazilian striker who is arguably the best footballer in the world, urged everyone, but particularly children, to do 30 minutes' exercise a day. 'Playing and training for football is a great way to have a heart for life,' he said.

A recent survey of patients across 15 European countries showed that, although two-thirds had been given advice about exercise from their GP, 61 per cent remained physically inactive.

The World Heart Federation, a Geneva-based group, was holding World Heart Day today to encourage healthier lifestyles. With the support of 180 medical organisations worldwide, it produced figures showing how people are becoming fatter and unhealthier at an alarming rate. About 30 per cent of all deaths are attributable to heart disease and strokes. At least 17 million people died from these causes in 1999 - 2.3 million more than died from cardiovascular disease in 1990.

According to the World Health Organisation, about one billion people are now overweight or obese. This is linked to the Westernisation of diets. Fruits, vegetables and whole grains are being replaced by junk food, high in saturated fat and added sugar.