New evidence from a UK study suggests that breastfed babies may be harder to soothe and cry more frequently than bottle-fed babies. But researchers say rather than being a sign of stress, irritability is a natural part of the communication between mothers and their infants and this should not put them off breastfeeding.

In a report published on 10 January in the journal PLoS ONE, the researchers describe how they studied a cohort of 316 babies aged 3 months. Mothers of breastfed infants reported their babies cried more and were harder to soothe than bottle-fed babies.

Lead researcher Dr Ken Ong, a Paediatrician from the Medical Research Council (MRC) Epidemiology Unit in Cambridge, said their findings do not contradict the “overwhelming body of evidence supporting breastfeeding as the normal and most healthy form of infant nutrition“.

“Bottle-fed babies may appear more content, but research suggests that these infants may be over-nourished and gain weight too quickly,” said Ong, “Our findings are essentially similar to other stages of life; people often find that eating is comforting.”

He said rather than being put off breastfeeding, parents should have “more realistic expectations” of what is normal infant behaviour, and they should get more understanding and support to help them if the behaviour is more difficult than they can cope with.

“These approaches could potentially promote successful breastfeeding, because currently many mothers attempt to breastfeed but give up after the first few weeks,” said Ong.

The UK government recommends that mothers exclusively breastfeed for the six months after birth.

The results of the 2005 Infant Feeding Survey, which collects information on infant feeding practices adopted by mothers from the birth of their baby up to around nine months, found that while three-quarters of UK mothers start out breastfeeding their babies, by the time their infants are four months old, only one third are breastfed.

The most common reason they gave was that “breast milk along didn’t satisfy my baby”, which suggests irritability is seen as a negative signal.

Professor Nick Wareham is Director of the MRC Epidemiology Unit. He said the study does not show a cause and effect (for instance it does not prove whether their baby’s irritability is what stops mothers breastfeeding), but it does offer some “fascinating insights” into the complex and dynamic communication between mothers and their babies.

“Understanding the determinants of infant feeding is a key step in designing appropriate interventions aimed at supporting healthy behaviours,” he added.

The data for the study came from the Cambridge Baby Growth Study, UK, where infant temperament is assessed at age 3 months by mothers completing the Revised Infant Behavior Questionnaire.

The researchers related the temperament scores to mode of feeding at 3 months (breast only, formula only, or mixed).

The results showed that compared to bottle-fed babies, exclusively breastfed and mixed fed babies were rated as having lower impulsivity and positive responses to stimulation, lower ability to regulate their own emotions, and higher emotional instability.

The researchers concluded that:

“Breast and mixed-fed infants were rated by their mothers as having more challenging temperaments in all three dimensions; particular subscales included greater distress, less smiling, laughing, and vocalisation, and lower soothability.”

“Increased awareness of the behavioural dynamics of breastfeeding, a better expectation of normal infant temperament and support to cope with difficult infant temperament could potentially help to promote successful breastfeeding,” they added.

Written by Catharine Paddock PhD