They looked at how babies coped with the pain of having blood taken from a vein, a procedure called venepuncture.

Drugs are rarely used to help babies with the pain of this and other procedures because of concern over their effectiveness and possible side effects.

The researchers decided to examine whether the pleasurable sensation of being breastfed would help the babies more than other strategies such as skin to skin contact with their mothers or having a dummy.

In the study, 180 healthy newborns studied were either breastfed, held in their mother's arms without being fed, given 1ml of glucose solution followed by a dummy or given 1ml of sterile water as placebo.

This has put something under the scientific microscope that mothers have known for quite a long time   Heather Welford, National Childbirth Trust

Standard pain measurement scales, and independent examination of videos of the procedure were used to assess how the babies reacted to the different methods of pain relief.

It was found that of the 44 babies who were breastfed, 16 showed no sign they had even noticed the venepuncture had taken place.

Babies who were just held in their mother's arms did not appear to experience any pain relief.

Comfort

The researchers, from the Unité Douleur Hôpital d'Enfants in Armand Trousseau, France, said this could be because they were dressed and had no skin to skin contact with their mothers.

They wrote in the British Medical Journal: "We have shown that breastfeeding is an analgesic.

"Our findings are clinically important as they show that natural protective mechanisms may safely and non-invasively be activated by breastfeeding during medical procedures.

Heather Welford, a breastfeeding counsellor and tutor for the National Childbirth Trust, told BBC News Online the research was additional evidence of the benefits of breastfeeding.

"This has put something under the scientific microscope that mothers have known for quite a long time.

"Some mothers will breastfeed during vaccinations because they know that their baby is likely to be soothed and comforted by it.

"Holding the baby and giving it a dummy did have some effect, they were better than nothing.

"But breastfeeding, which involves holding, skin to skin contact and the pleasure and comfort of feeding, seems to have everything together."