Breastfeeding may be the ultimate natural painkiller for newborn babies.
Breastfeeding may offer comfort
A review of research found that breastfeeding newborns helps relieve the pain from a needle prick used to screen their blood for disease.
Breastfed babies appeared to experience less pain than those who were swaddled, given a dummy, or a placebo. Comfort from a mother's presence may be key.
The Cochrane Library review, by Toronto's Mount Sinai Hospital, was based on data from over 1,000 babies.
The researchers say that breastfeeding could possibly help relieve pain for premature babies who need to undergo many painful intensive care procedures.
However, they stress that their study did not test the impact of breastfeeding on the pain associated with repeated procedures.
The Mount Sinai team assessed pain by measuring changes in heart and breathing rates, and the length of time a baby cried after receiving the needle prick.
The researchers say that the key to the effect of breastfeeding may be that an infant simply draws comfort from the close proximity of its mother.
Alternatively, breastfeeding may help to divert attention away from the pain of a needle prick.
They also suggest that the sweetness of breast milk may be a factor.
Another theory is that breast milk contains a high concentration of a chemical which could ultimately trigger the production of natural painkillers called endorphins.
The researchers also found that giving babies a sugar solution seemed to be effective.
But researcher Dr Prakeshkumar Shah said: "Based on this review we concluded that for a neonate undergoing painful procedure breastfeeding is superior to no treatment, placebo, or swaddling alone for relieving pain.
"As it is the most inexpensive, safe and advantageous from other perspectives, it should be offered to all neonates to relieve procedural pain when possible."
Dr Tony Williams, an expert in neonatal care at London's St George's Hospital, said: "Newborn babies are often given dummies soaked in concentrated glucose to help reduce distress during painful procedures.
"This study shows that babies would do just as well by being breastfed."