Breastfeeding: Separating Myths from Facts
BBC Radio Jersey says:
“Jersey's Home Affairs Minister Kristina Moore has been
appointed the island's breastfeeding champion. The recently published Health
and Nutrition strategy highlighted breastfeeding as an important way of
preventing obesity in children.”
But actually the evidence is very uncertain on any direct
link. This is because of a problem in statistics known as “confounding”.
Attempts have been made to try and bypass the problems in studies, but there is
no clear way of showing that they do.
The website Pmean explains exactly what confounding means in
statistics:
“Residual confounding occurs when a confounding variable is
measured imperfectly or with some error and the adjustment using this imperfect
measure does not completely remove the effect of the confounding variable. An
example appears in Chen et al (1999). It turns out that women who smoke during
pregnancy have a decreased risk of having a Down syndrome birth. This is
puzzling, as smoking is not often thought of as a good thing to do. Should we
ask women to start smoking during pregnancy?”
“It turns out that there is a relationship between age and
smoking during pregnancy, with younger women being more likely to indulge in
this bad habit. Younger women are also less likely to give birth to a child
with Down syndrome. When you adjust the model relating smoking and Down
syndrome for the important covariate of age, then the effect of smoking
disappears. But when you make the adjustment using a binary variable (age<35 age="" years="">=35 years), the protective effect of smoking appears to remain.
This is an example of residual confounding.”
The effects of confounding of this nature is most clearly
stated in the WHO publication “Long-term effects of breastfeeding: A Systematic
Review” by Bernardo L. Horta, MD, PhD and Cesar G. Victora, MD, PhD.
“Residual confounding is another issue that should be
addressed, because most studies were carried out in high-income countries where
breastfeeding tends to be more common among the better off and more educated
mothers. In these societies, overweight and obesity tend to be more prevalent among
the poor, and even studies that adjusted for several socioeconomic variables
may still be affected by residual confounding.”
“Attempting to elucidate this possibility, Brion et al
compared the effects of breastfeeding on body mass index in two settings with
different socioeconomic confounding structures. In England, a developed country
setting, breastfeeding was protective against overweight, but in Brazil, where
breastfeeding does not show a clear social gradient, no such effect was
evident.”
“This was confirmed by the negative findings of the COHORTS
collaboration from low and middle-income countries . Therefore, residual
confounding by socioeconomic status is an issue that should be taken into
consideration in the assessment of causality. By the same token, we observed
that studies with tighter control of confounding (socioeconomic factors, birth
weight or gestational age, and parental anthropometry) reported smaller
benefits of breastfeeding.
“Our conclusion is that the meta-analysis of higher-quality
studies suggests a small reduction, of about 10%, in the prevalence of
overweight or obesity in children exposed to longer durations of breastfeeding.”
“Nevertheless, it is not possible to completely rule out residual
confounding because in most study settings breastfeeding duration was higher in
families where the parents were more educated and had higher income levels.”
Another source of “proof” is by what are called “meta-analyses”
which seek to try an collate all the publications and data published on a
subject such as breast-feed. Meta-analysis is the statistical procedure which
combines data from multiple studies. This has been used also to link
breastfeeding with obesity, but it also contains problems. The Journal on
Nutrition notes that there are several drawbacks that limit the validity of
meta-analyses of observational studies on associations of breastfeeding and
body composition in childhood:
1) Publication bias: Studies with significant results may be
more likely to be published than studies without significant results. This may
also bias the results from meta-analyses.
2) Potential heterogeneity between studies: Individual
studies may differ largely from each other with respect to the study population
or confounders considered, which complicates approaches to provide a summary
estimate.
3) Residual confounding: Breastfeeding is associated with
other factors that can influence a child's weight status, such as maternal BMI,
maternal education, smoking during pregnancy, or other habits that may not be
able to be comprehensively assessed in epidemiologic studies. However, a
failure to adjust for these factors may result in spurious associations, which
may also contribute to a bias in meta-analyses.
It concludes that:
“Observational studies (and related meta-analyses) may
suffer from a publication bias or residual confounding. Interventional studies
that randomly assign breastfeeding itself are not feasible, whereas
interventional studies that randomly assign a breastfeeding promotion would
require enormously large sample sizes.”
And notes that:
“Whether or not breastfeeding also has a weak positive
effect on body composition may be an interesting question, but this does not
necessarily need to be answered to recommend breastfeeding to mothers of
newborns. With respect to the avoidance of childhood overweight, strategies
aimed at eating or activity habits may be more promising than a breastfeeding
promotion.”
Mainly Personal
If there was a causal mechanism linking breastmilk with obesity,
what could it be?
Feldman-Winter says it may be that both breastfeeding — with
the baby attached to mom’s breast — and the breast milk that may be important
in influencing babies’ weight. In suckling, it’s the baby that dictates how
much he drinks, whereas with bottle-feeding, whether it’s breast milk or
formula, it’s mom that tends to determine when baby has had enough. “A baby who
is breastfeeding at the breast will suckle, and some of that time will be spent
in nutritive suckling and some of that time in getting nourishment, but a lot
of the time babies are suckling at the breast in a non-nutritive way and really
self regulating the amount of calories they take in,” she says.
“Breast milk provides your baby with food that is easy to
digest and very nutritious, and your child helps decide how much to eat and
when to eat it. Both the breast milk itself and the way your baby feeds help
him or her to develop healthy eating patterns. Breastfed babies seem to be
better able to regulate their food intake and thus are at lower risk for
obesity.”
That’s very interesting because in the case of one of my
sons, he was unable to take milk from breastfeeding, and was noted down as
potential having a “failure to thrive”. A bottle regime, where the amount
consumed along with date and time was suggested by the resident hospital head paediatrician,
Dr Spratt, as the average could be carefully noted, along with the total amount
consumed. So in this case, the determination of how much to drink did not work,
and a bottle was the sufficient remedy. Part of the problem is with “failure to
thrive” is that the mother may well feel that her child was satisfied with the
feedings.
Having looked at this, I notice some other cases, not many,
but still significant, in which this has happened. With my son, the
preventative measures were in place early, but this is not always the case.
One mother reported that:
“My fourth baby ended up hospitalized for failure to thrive
and required a nasogastric tube to feed her. Despite constant breastfeeding,
excellent milk supply and milk transfer, she never gained enough weight and
then began losing weight. She was born weighing 8 pounds and when admitted to
the hospital she weighed 9 pounds, 5 ounces.”
“I worked in labor and delivery and postpartum units as a
tech and then a registered nurse for 6 years at a BFHI designated hospital and
I was so indoctrinated by “Breast is Best” that I truly believed “a hungry baby
wouldn’t starve” and every mother can exclusively breastfeed, including me.
“Elena’s doctors ordered her to begin feedings with a 24
calorie formula for the first creecy2months and then she was fed a 22 calorie
formula to help her gain enough catch-up weight. We were able to remove her
feeding tube after a month when she began to gain weight and thrive and
eventually she was transitioned to a regular 20 calorie formula.”
As Dr.Shannon Kelleher, a human milk researcher (“Biological
underpinnings of breastfeeding challenges: the role of genetics, diet, and
environment on lactation physiology”, 2016) noted:
“If you think about it, when you’re breastfeeding you have
no idea how much milk you are producing or if the composition is optimal and as
long as your baby isn’t overtly ill, you assume that everything is working
well. But is it?”
“It is estimated that the prevalence of women who overtly
fail to produce enough milk may be as high as 10–15% and can quickly lead to hypernatremia (high
blood sodium levels) nutritional
deficiencies, or failure to thrive;”
“It is estimated that approximately 10-15% of women suffer
from overt lactation failure. This is different from what I consider ‘breast
milk insufficiency’. When I talk about ‘breast milk insufficiency’” I’m
referring to the inability to make enough milk of optimal quality to feed the
baby.”
“A woman’s genetics is very important to providing enough
zinc to breast milk. Others have shown that genetic variation in the vitamin D
receptor affects milk calcium levels, and that genetic variation in genes that
produce fatty acids, alter the fatty acid composition of human milk.”
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