Children regularly fed milk containing so-called "friendly bacteria" developed fewer respiratory infections, scientists found.

It is the latest in a number of studies suggesting potential health benefits of taking probiotic supplements.

The slight reduction in respiratory illness was found among Finnish children attending day care - who traditionally suffer higher illness rates than those looked after at home.

A total of 571 children were given either normal milk or milk with an added strain of Lactobacillus - a type of bacteria which can be found naturally in the gut.

Children drank at least 200ml of their milk every day.

Children given Lactobacillus had on average a day less absence from day care.

There was also a 17% reduction in those suffering more serious respiratory tract infections. Consequently, they were prescribed fewer antibiotics.

Allergies

Although other studies have suggested that probiotic diets might help ward off allergies and gut problems, there was no difference in allergic symptoms or abdominal pain between the two groups.

The authors of the study suggested that the cost to Finnish society due to illnesses among day care children was between �650 and �2300 per child.

Dr Anne McCartney, a researcher into probiotics at Reading University, said that the jury was still out on the ability of probiotics to prevent disease.

She told BBC News Online: "There is nothing really known about the mechanism by which this works.

"A lot of probiotic people or companies which sell them suggest ways they could work - such as by stimulating the immune function of the gut."

The study was published in the British Medical Journal.