Wednesday January 11 2012
Research on breast-fed babies gives clues to their temperament
“Is breast really best?” asked the Daily Mail today. A study has found that babies fed on formula cry less and are easier to get to sleep, it reported.
However, this study does not prove that breastfeeding results in unhappier babies, or that formula feeding is better.
The Mail’s story is based on research that asked mothers of three-month-old babies to report how their babies were fed and how they assessed their babies’ temperament. It found that at three months, breastfed babies and babies that were both breastfed and formula-fed were rated by their mothers as having more “challenging” temperaments than formula-fed babies. Breastfed babies were reported to show more distress, to smile and laugh less and to be more difficult to soothe.
The findings from this small study appear to tell new mothers that feeding a newborn baby formula has an advantage over breastfeeding. However, it cannot prove that the babies’ feeding method directly caused their behaviour, and did not consider wider issues such as:
- factors that influenced the choice of feeding method
- whether the mother worked
- other children in the home
- mother’s educational achievement and their perception of infant temperament
The differences in temperament scores were very small, and it is not possible to say whether these would have meant noticeable differences in the day-to-day temperament of the babies. As the study relied on the mothers to complete questionnaires, the responses are likely to be subjective.
As the researchers point out, crying and irritability are normal ways for babies to signal they are hungry. They also say that new mothers often worry that their babies are not satisfied by breastfeeding, and that they may benefit from being advised how their baby is likely to behave when breastfed.
The Department of Health recommends that mothers exclusively breastfeed for the first six months after birth, and this research does not alter this advice.
Where did the story come from?
The study was carried out by researchers from the Medical Research Council, Cambridge, University of Cambridge, University College London and Universite Paris-Sud, France. It was funded by several institutions including the EU and the MRC. It was published in the peer-reviewed journal Public Library of Sciences One.
The story was covered reasonably well by the papers, although the Mail’s headline, which asked whether breast is “really best”, was misleading. The study does not question the benefits of breastfeeding, which are well established. The Mail did, however, include comments from independent experts who extolled the virtues of breastfeeding.
What kind of research was this?
This cross sectional assessment was taken from a larger, ongoing cohort study, which intends to look at factors before and after birth that may influence infant weight gain. This particular snapshot examined whether there was a relationship between breastfeeding and infant temperament (as rated by the mother) at three months old. Though a cohort study can be useful for examining whether a certain exposure affects the risk of a particular outcome, a cross sectional assessment within a cohort cannot prove causation or explain the reasons for any apparent link between observations.
As the researchers point out, although the benefits of breastfeeding are well established, rates of breastfeeding remain low in the UK and similar countries. Just over a third of mothers who opt to breastfeed are still doing so at four months, and the researchers cite evidence that the most common reason for mothers to stop breastfeeding is that “breastfeeding alone didn’t satisfy my baby”.
What did the research involve?
For this cross sectional assessment, the researchers used 316 infants, born between 2006 and 2009 to mothers attending an antenatal centre in Cambridge. To be included, the mothers had to be over 16 and able to give informed consent. The babies in the study were a small sample of the larger cohort (1,526 at the time of the study). They were sampled because data were available for them on temperament and feeding at three months of age. They were representative of birth weight, mothers’ weight (BMI) and method of infant feeding at three months in the larger cohort.
The researchers measured the babies’ temperaments at the age of three months, as assessed by the mothers. They used an established infant behaviour questionnaire (the Revised Infant Behavior Questionnaire), which included 191 questions on “three major dimensions” of infant temperament. These were:
- Surgency/extroversion, which means cheerfulness or sociability: higher scores are seen in infants with high activity levels, impulsivity and positive response to highly stimulating situations.
- Negative affectivity: higher scores indicate higher distress or irritability and emotional instability.
- Orienting/regulation: higher scores indicate greater ability to be soothed easily and to regulate their own emotions.
Questions were asked about how much babies smiled or laughed during play, how often babies cooed, how much distress they showed when being washed or changed, how easily they were to soothe, and how much pleasure they expressed at being hugged.
In a separate nurse-administered questionnaire, the mothers were asked whether babies were being breastfed, formula-fed or both (mixed feeding) at three months. Researchers also collected other data including socioeconomic details and height and weight.
They analysed the associations between infant temperament and feeding method using standard statistical methods. They adjusted their findings for factors indicating deprivation.
What were the basic results?
The researchers included 171 boys and 145 girls in their analysis. Of them, 137 babies were exclusively breastfed at three months, 88 were exclusively formula-fed and 91 were fed with a mixture of formula and breastfeeding.
They found that compared to formula-fed babies, exclusively breastfed and mixed-fed babies had:
- lower impulsivity and lower positive responses to stimulation (overall surgency/extraversion score 4.3 in formula-fed and 4.0 in both mixed-fed and breastfed groups)
- lower ability to regulate their own emotions (overall orienting/regulation score 5.1 in formula-fed and 4.9 in both mixed-fed and breastfed groups)
- higher emotional instability (overall negative affectivity score 2.8 in formula-fed and 3.0 in both mixed-fed and breastfed groups)
How did the researchers interpret the results?
The researchers concluded that breast- and mixed-fed babies are rated by their mothers as having more “challenging” temperaments, in particular showing greater distress, less smiling and cooing and lower soothability. However, they point out that although humans perceive infant crying as stress, for infant animals, irritability is a normal component of “signalling” nutritional demands to parents and that the same dynamic has been observed in humans.
They conclude that breastfeeding may be demanding for both mothers and babies but the findings should not be taken to discourage mothers from breastfeeding. Mothers should be given more realistic expectations about infant temperament and more support to cope with the difficult aspects of breastfeeding.
This cross sectional assessment, taken within part of a large cohort, asked mothers of three-month-old babies to report how their babies were fed and to complete a questionnaire which assessed their babies’ temperament. Most importantly, this assessment cannot prove causation, and does not mean that breastfeeding results in unhappier babies or that formula feeding is better.
There are several additional points to make:
- The researchers did not take into account other wider issues that might affect the chosen feeding method, mother/baby interactions and babies’ temperaments, such as whether the mothers were working, time spent with babies and feeding schedules.
- The study relied on mothers to subjectively rate their babies’ temperaments. Such self-completed ratings could be influenced by other things, such as the mothers’ anxiety about breastfeeding.
- The differences in temperament between breastfed and formula-fed babies as rated by the mothers appeared to be small. For example, the emotional instability score was 2.8 in the bottle-fed group and 3.0 in breastfed and mixed-fed babies. It is not possible to say whether these small score differences would have made appreciable differences in the day-to-day temperament of the babies.
- Educational achievement of women who breastfed or mixed-fed their babies was higher, and how this might have influenced their scoring of temperament was not discussed by the authors.
- It is not known whether the current method of feeding at three months represents a consistent pattern since birth or whether there have been changes. For example, a baby described as formula-fed at three months may have only just been switched to formula feeding and may have been exclusively breastfed up until then. Finally, as the researchers point out, this small study of mothers and babies in Cambridge may not be representative of UK mothers and babies generally.
Nevertheless, the study provides some useful information about the possible differences in temperament between breastfed and formula-fed babies, and the researchers make suggestions as to why these might occur.
As one midwife reportedly pointed out, new mothers may be unconfident about breastfeeding and reach for formula to “settle” an apparently unhappy baby. Learning more about babies’ temperaments and the signals they are giving could help allay maternal anxieties and boost breastfeeding rates.
This research does not alter current advice from the Department of Health, which recommends that mothers exclusively breastfeed for the first six months after birth.