New Study: Exclusive Breastfeeding Can Support Infant Growth to 6 Months of Age

A new study published this week in the journal Pediatrics found that exclusive breastfeeding up to six months provides enough calories for infants.

 

Quick and Dirty Summary:

This study addressed two common concerns about breastfeeding:  1) Many moms simply can’t produce enough milk for their babies; and 2) Exclusive breastfeeding, while adequate in younger infants, may not provide enough calories for babies up to 6 months of age.  The data from this study indicate that when moms are given breastfeeding support, milk production is not a limiting factor and provides enough calories for normal growth, even in 6-month-old infants.  However, this study was small and had several limitations (which I will discuss). 

 

How was this study conducted?

This was a longitudinal study of 50 mothers and their infants in Glasgow, Scotland.  All of these mothers intended to exclusively breastfeed (EBF) for at least 6 months and were recruited from breastfeeding support groups, so we can presume that they were already set up to succeed with breastfeeding.  EBF is defined by the World Health Organization (WHO) and in this study as giving the infant only breast milk for nutrition (no solids or formula), with oral rehydration, vitamins, minerals, or medicines allowed as needed.  60 mothers were recruited, but only 50 were still EBF at the first assessment around 15 weeks of age.  Assessments included measurements of infant growth, milk intake, total energy intake, and milk energy content.  Mothers also completed questionnaires and infant behavior diaries in order quantify the number of feedings and total time spent nursing.  These measurements were all repeated at 25 weeks of age (6 months).  At this second time-point, 3 mothers had dropped out of the study and 41 mothers were still EBF.  The remaining 6 mothers had begun feeding their babies some solid foods. 

How, you might ask, did the researchers manage to measure milk intake in nursing babies?

Excellent question.  They used a technique called the doubly-labeled water method, which involves feeding the baby a tiny and safe dose of stable isotope-labeled water (²H₂¹⁸O) and then collecting samples of their pee (which is easy enough to do when you change a diaper) to measure how long it takes those isotopes to come out.  Then they did a bunch of calculations.  Really.  Trust me when I tell you that this method is safe, non-invasive, and pretty much the best way to measure milk intake in nursing babies.  I’ve actually had a little experience  (in a previous life) using this method in nursing bottle-nosed dolphins.

What are the most important findings of the study?

-The exclusively breast fed infants in this study grew just fine, right in line with the WHO Child Growth Standards.  EBF to 6 months didn’t set them back in their growth curves.

-Milk intake was slightly but significantly higher at 25 weeks compared with 15 weeks (997 vs. 923 grams; P=0.001), showing that milk production increased to meet the increasing demands of the infant.  Milk energy content (as in calories per liter) did not change between time points.

-Moms reported breastfeeding 8-9 times per day at both 15 and 25 weeks, but time spent feeding decreased from 173 minutes per day at 15 weeks to 140 minutes at 25 weeks.  That means that at 25 weeks of age, babies were drinking more milk but doing so more efficiently than at 15 weeks.  No surprise there.

 

-There was no difference in infant weight or milk intake at 25 weeks between the EBF infants and the 6 that had started solid foods.  The moms of these babies said they started solids because their babies seemed ready.

What can we conclude from this study?

The study shows that in most women with good breastfeeding support, infant milk intake is sufficient to support normal growth with EBF for 6 months. 

The authors of the study assert that their findings support the recommendation that all babies should be EBF for the first 6 months, but there are some problems with jumping to that conclusion… 

What are the limitations of the study?

-10 of the 60 moms initially enrolled in the study were not still exclusively breastfeeding at 15 weeks, and the study authors don’t tell us what happened to those 10 women.  Did they stop breastfeeding or supplement with formula because of a fear, real or not, that they weren’t producing enough milk?  We just don’t know.

-The mothers in this study were older (mean age 33) and more affluent than the average mom.  They were highly motivated to exclusively breastfeed and had good support to do so.  Just guessing, but this type of mom is also more likely to take good care of herself and have support at home to do that.  All of those factors might impact her breastfeeding success.

-The 6 babies that started solid foods prior to 6 months had similar caloric intake from milk as the EBF babies.  These babies were also getting some additional calories from food, but the study did not report this.  It is possible that these babies were truly ready for solids before 6 months and needed the added energy from solids, in addition to breastmilk.  The authors don’t address this possibility.  

-This study only looked at calories from milk intake.  It doesn’t consider micronutrients such as iron and zinc that may become limiting at this age without the addition of some solid foods in the diet. 

My take: 

This study shows that exclusive breastfeeding to 6 months can provide enough energy to support normal growth in babies.  However, the mothers in this study were highly-motivated and had great support for breastfeeding.  We don't know why 10 women dropped out of the study or if the babies consuming solid foods actually needed the additional calories from that food. Due to these limitations, the results of this study may not apply to the general population.

It is easy to over-simplify the results of a study like this, but when we really look at the data, we find that it just isn’t that simple.  Unfortunately, most science isn’t.

The perception of low milk supply remains a major barrier to exclusive breastfeeding, and more work needs to be done to show whether or not this is a physiological or psychosocial problem. 

What do you think?  Did you or a friend have a problem with low milk supply?  There is nothing worse than thinking that your baby is hungry and not being able to feed her!

New Study: Harsh Discipline is Associated with More Behavioral Problems

There was an interesting study published online this week in the journal Pediatrics:

 

The most important finding of this study was that harsh discipline tactics don’t lead to healthy, well-behaved children.

This was a longitudinal study (meaning that the same groups of kids were studied at several different time points) of Australian children in which 5107 infants (3-19 months) were monitored several times up until age 4-5 years and 4983 preschoolers (4-5-year-olds) were monitored up until age 8-9 years.  Between enrollment in the study and the final assessment, 86% and 87% of the infants and preschoolers, respectively, remained in the study.  That makes this a relatively large study with a good retention rate. 

Child mental health was assessed with the Strengths and Difficulties Questionnaire.  The SDQ, which can be downloaded in just about any language HERE, asks the parent or caregiver to mark whether statements about their children are “not true,” “somewhat true,” or “certainly true.”  For example, the SDQ asks if your child is “restless, overactive, cannot stay still for long,” or is “nervous or clingy in new situations, easily loses confidence.”

The study authors used the SDQ to determine if children had symptoms of externalizing or internalizing mental health problems.  Externalizing problems are related to aggression and oppositional defiance.  Internalizing problems include anxiety and depression.  Among the kids in this study, 20% had externalizing problems and 24% had internalizing problems at 6-7 years of age.  In the 8-9-year-old group, 17% had externalizing and 24% had internalizing problems. 

The researchers measured a wide array of potential risk factors for mental health issues, including family factors (such as mother’s age, education, single parent home, socioeconomic status), child factors (sex, race, physical health, language development, sibling), parenting practices, mother’s mental health, various family life stressors (conflicts, grief/illness, job quality), and community factors (type of childcare, rough neighborhoods).  I would say that the study was fairly comprehensive in measuring a wide range of factors that might influence a child’s mental health.  However, a major limitation of the study was that they didn’t look at the fathers at all, except for noting whether or not they were present – nothing on the fathers’ mental health or parenting practices. 

The researchers built statistical models in which they tried to explain the children’s mental health outcomes using all of those risk factors that I just listed.  They found that 20-30% (depending on the group) of mental health problems were associated with the risk factors I listed above.  The other 70-80% are associated with factors that the study didn’t examine, such as genetics, exercise, diet, or factors related to the kids’ fathers.  20-30% doesn’t seem like much, but that isn’t surprising when you consider that behavior and mental health are so complicated. 

Here are the most important findings of this study:

Of all of the potential risk factors that I listed above, harsh discipline was the strongest and most consistent predictor of externalizing problems in both age groups evaluated.  That is, as defined in this study, kids that were smacked or yelled at were more likely to be aggressive and defiant. 

Internalizing problems (anxiety and depression) were also higher in kids who were harshly disciplined, but in addition were consistently associated with kids with health problems, only children, and maternal emotional stress.  In the 4-5-year-olds, over-involved and over-protective parenting styles were also associated with internalizing problems.

A limitation of any longitudinal study like this one is that it is purely observational.  It can show that factors are associated with one another, but it can’t prove a causal relationship.  That is, this study can’t prove that harsh discipline causes more behavioral problems, it only says that kids that are disciplined harshly also have more behavioral problems.  This can lead to chicken and egg type questions.  For example, it is possible that kids that the kids are disciplined harshly because for whatever reason they have more behavioral problems, and their parents just don’t know how else to respond.  Finding out if harsh discipline makes the situation worse would require a study with an intervention – something that would compare two groups of kids, one whose parents had coaching on respectful, nonviolent discipline and another whose parents did not.  Either way, this study does show that in kids with behavioral problems, yelling and hitting are not an effective discipline strategy.  If harsh discipline worked, then the study would have shown that it was associated with kids without problems.

I wasn’t surprised by these findings, and you probably aren’t either.  Here’s why the study is important:  It gives people who work with young kids and their parents specific risk factors to watch for.  Pediatricians, educators, and social workers can use these factors to identify high-risk kids, check in with them, and talk with kids and their parents about mental health.  They might mention that hitting and yelling at kids doesn’t resolve their behavioral problems, at least not in Australia.

One surprise finding…

Mothers who had at least two alcoholic drinks per day had kids with fewer externalizing and internalizing problems.  Having been on the science side of research before, I can just imagine the authors of this study groaning when they found this result.  They tried to find another way to explain it but couldn’t.  That’s science for you.  It doesn’t always make sense.  The authors of this study guess that this particular finding is “attributable to chance.”  It is more fun to imagine that these moms put their feet up and enjoyed a couple of glasses of wine after the kids went to bed, maybe helping to offset some of that maternal emotional distress. 

Pure speculation on my part (NOT medical advice!), but on that note, I think I’m done for the night:)