It is not clear why, but closer contact between mother and child may be a factor.

Breast feeding for at least four months was linked with a slightly lower risk of sudden infant deaths (SIDS).

Previous studies in Sweden, England and Scotland have found no connection between the two.

However, research carried out in New Zealand did find some protection against cot death with breast feeding.

The Scandinavian scientists say it is unclear what causes this "protective effect".

"One possibility could be that breast fed infants had a lower risk of infection," Dr Bernt Alm and colleagues write in a report in The Archives of Disease in Childhood.

"It is also possible that frequent feeding of the infant, and the resultant closer contact between mother and child, decreases the risk," they add.

'Weak relation'

Dr Alm's team at the Institute for the Health of Women and Children in Gothenburg, Sweden, questioned the parents of 244 babies who had died of cot death in Sweden, Denmark and Norway.

They compared the results with a survey of the parents of more than 800 healthy babies.

They found that babies who had been breast-fed for less than eight weeks had between three and five times the risk of dying from cot death compared with those fed naturally by their mother for four months or more.

"The study is supportive of a weak relation between breast feeding and SIDS reduction," Dr Alm said.

UK charity, the Foundation for the Study of Infant Deaths (FSID), said the finding was interesting although not conclusive.

'Good practice'

"This needs to be replicated in the UK, where breast-feeding rates are much lower," said a spokesperson.

"Research in the UK has so far failed to show that breast-feeding helps protect against cot death.

"However FSID has always recommended breast-feeding as a matter of good infant care practice and to help increase baby's resistance to infection."

A campaign to encourage parents to put babies to sleep on their backs has reduced the number of babies dying from the condition.

Parents are also advised to stop smoking, make sure their babies sleep on a clean mattress and not to let them get too hot.

As well as the possible link with cot death, breastfeeding has been shown to reduce the risk of ear infections, obesity, allergies, vomiting and diarrhoea.

Rosie Dodds, policy and research officer at the National Childbirth Trust, said: "This is another important characteristic to add to a long list of health benefits associated with breastfeeding for both the mother and baby."