concerning the merits of breast feeding
rages still (unfortunately). Over the past fifty years, there has been a huge swing
from a very strong pro-formula
position to a pro-breastfeeding position both in general society
and within the medical field
. This swing has been partly driven by
scientific findings about the advantage
breast milk has for the infant
: faster and more thorough immune system
development, lower infection
rates, greater resistance to
s, reduced chances and
severity of colic
, greater intelligence, etc1
. However, very recently (21 September 2002) a fascinating
was published in The Lancet
, one of the premiere international medical journals. The study found that
breastfeeding a child for more than four
weeks led to an increased risk of developing asthma
or skin allergies
later in life (ages 9 to 26). This finding is of particular interest to
the medical community since
previous studies have produced contradict
ory results and have suffered from a number of methodological shortcomings
. It is also of
great interest to the general public, as
these findings fly in the face of current wisdom
. For these reasons, this write-up will deal principally with the contents of this paper,
given that most private citizens will
have a very time obtaining a copy of the publication. Some popular press
concerning this study can be found at the
There are other news stories around the web, as this study has already garnered a lot of attention
is your friend.
The purpose of this write-up is not to simply re-iterate the information found in the above articles, or that easily found on the web by
interested parties. Instead, it will
present an abridged and 'vulgarized' version of the paper itself, which will be followed by a brief commentary and critique.
Directly from the article (the Background
, which is part of the abstract):
Breastfeeding is widely advocated to reduce risk of atopy and asthma, but the evidence for such an effect is conflicting. We aimed to
assess the long-term outcomes of
asthma and atopy related to breastfeeding in a New Zealand birth cohort.
While many in the medical community and much of the scientific literature suggests that breastfeeding of infants should be pursued in
order to reduce the risks of later
development of atopy and asthma, studies prior to this one had produced some contradictory results. As a result, a 1988
by M. S. Kramer proposed
12 criteria for future studies which wish to examine the relationship
between breastfeeding and asthma, and based on these 12 criteria
found that most previous studies were lacking in rigour
(thus making their findings suspect). Despite this important paper, further studies continued to appear with
contradictory results and again (possibly)
improper methodologies. The authors of the Lancet study followed the Kramer protocol
s to try to ensure that their study would
produce defensible results
Non-reliance on late maternal recall of breastfeeding
Blind ascertainment of infant feeding history
Sufficient duration of breastfeeding
Sufficient exclusivity of breastfeeding
Strict diagnostic criteria
Blind ascertainment of outcomes
Consideration of severity of outcome
Consideration of age of onset of outcome
Control for confounding
Assessment of dose-response effects
Assessment of effects in children at high risk of outcome
Adequate statistical power
The authors initiated their study with the hypothesis that breastfed children would display a lower incidence of asthma and atopy later in
The authors of the Lancet study had the opportunity to test, rigorously, the relationship between breastfeeding, asthma and atopy
thanks to a study iniated in 1972 at the
Queen Mary Hospital in Dunedin, New Zealand. A cohort of children born between April of 1972 and March of 1973 were included in a
neonatal study. Those children still
residing in the province of Otago at 3 years of age (1975-76) were invited to participate in the longitudinal Dunedin Multidisciplinary
Health and Development Research
Study. In total, 1037 children were enrolled, and these children form the basis of the paper being discussed. The families of these
children spanned the entire
socio-economic range of the general New Zealand population, and were mostly caucasian. The socio-economic status of the families
was, however, recorded on a
semi-quantitative scale (Elley-Irving scale) for later use in statistical models.
The 1037 children in the study were assessed for a number of conditions and their general health within a month of their date of birth
at ages 3, 5, 7, 9, 11, 13, 15, 18, 21
and 26. They were accompanied by their parents during their assessments up to the age of 11, and were examined individually
thereafter. Of course, not all children were
present and tested for their respiratory condition at each year of investigation, but the representation was very good (from 71% for
age 7 to 96% at age 26). Skin testing
(for atopy) was conducted only at ages 13 and 21, again on a subset of the whole cohort (69% and 87% respectively).
The breastfeeding history was documented by independent interviewers at age 3. The duration of breastfeeding and the age at which
cow's milk was introduced were
recorded by the interviewer and verified against the information gathered through the New Zealand Plunket Nurse programme, where
nurses see mother and child both in
clinics and at the home every week after birth and then less frequently until the age of 2 or 3. While those children who were breastfed
did often receive formula during
night feedings while at the hospital, this was only for 3 or at most 4 days, and the researchers considered this quantity to be insufficient
to eliminate the benefits associated
with breastfeeding. A participant was considered to be a member of the breastfed group if the child had been exclusively breastfed for
at least four weeks. Using this
classification, 45% of the children were not breastfed, 49% were breastfed and 7% were breastfed initially, but were moved to formula
before the child was 4 weeks old
(for a variety of reasons). This latter group was statistically indistinguishable from the non-breastfed cohort, and thus was included in
the non-breastfed group. For the breast-fed
cohort, the mean duration of breastfeeding was 21.1 weeks.
At age 7, trained interviewers asked the parent whether the child suffered from asthma, hayfever, wheezing or other respiratory
problems. During this same interview,
family history of asthma or respiratory problems was also recorded. At age 9 a more comprehensive questionnaire was introduced,
wherein the frequency and occurrence
of asthma or wheezing was recorded. At ages 18, 21 and 26 the participants completed questionnaires based on those from the
American Thoracic Society and the
International Union Against Tuberculosis and Lung Diseases. Those participants using bronchodilators were asked to withhold on the
day of the study, and all individuals
were tested using a spirometer. After an intial test in which the forced exhaled volume (FEV) and vital capacity were recorded,
treatment with methacholine was performed
and spirometry repeated. Presence of a respiratory problem or defect was recorded for the participant if their FEV was reduced by 20%
or more following treatment with
methacholine. In the case of children already showing signs of respiratory distress, the patients were treated instead with salbutamol
and a problem or defect was
if their FEV improved by over 10%.
To test for the presence of atopy, skin prick tests were performed at ages 13 and 21. Participants were excluded from this trial if they
had used antihistamines within the 2
days prior to the investigation. The allergens tested were dust mites, rye grass pollen, cat dander, dog dander, horse hair, kapok,
fumigatus, Penicillium spp., Althernaria spp. and wool, with both a positive and negative control. After 15 minutes,
an positive test was recorded if the
pin prick produced a weal at least 2 mm larger than the negative control.
Statistical analyses were performed on these data to determine first whether there was any difference between the breastfed and
non-breastfed children with respect to
occurrence of asthma and atopy. The initial tests used were simple chi-squared and likelihood ratio tests to compare the breastfed to
non-breastfed groups. Later,
multivariate methods were used in a step-forward manner in order to attempt to control for some confounding factors.
Whenever you perform a mensurative study, some things are beyond your control. In the case of this study,
the breastfed and non-breastfed
cohorts were not identical. Children were more often breastfed if they were first born, if their parents were of higher socioecononmic
status or if their mothers were
non-smokers. Breastfed children were also more likely to have had sheepskin on their bed in infancy. Luckily for the researchers,
these three factors would suggest that
breastfed cohort may have been biased to having a lower risk of asthma or allergies, while they found the opposite relationship to be
At age 13, positive skin tests to cat, house dust mites, grass, alternaria or any other allergen were more likely to occur in the breastfed
cohort. This same pattern was
repeated in the tests conducted at age 21. In fact, the odds ratios (ie., the risk of showing a response in the breastfed group / risk in
the non-breastfed group) ranged from
1.48 to 2.41 for these tests, meaning that breastfed children were as much as two and one-half times more likely to show an allergic
response. The same pattern was
repeated when examining the evidence of asthma or respiratory distress. At every age from 9 to 26, breastfed children were more
likely to report having asthma than
counterparts. The odds ratios varied from 1.50 to 2.93 (three times!). The same pattern was uncovered when examining the
respirometry results before and after
treatment with methacholine or salbutamol: significant increases in the incidence of distress were observed in the breastfed cohort in
every case, except for those children
wheezing (not diagnosed as asthmatic) at age 15.
When the data were examined in a more intensive manner, it was found that any breastfeeding beyond the age of three weeks
resulted in an increase in the risk of atopy
at age 13. For example, while those children never breastfed or breastfed for fewer than four weeks had a 37% and 34% risk of
displaying atopy to at least one of the
tested allergens, those breastfed for 4-7, 8-11, 12-15, 16-25 and more than 26 weeks had 58%, 49%, 68%, 48% and 46% chances of
showing such a response. This same
pattern was found when testing for the incidence of atopy at 21 years or asthma at 9 years of age.
As should be expected, those children from families with a parental history of hayfever or asthma developed atopy or asthma at a
greater rate than their counterparts,
irrespective of whether they were breastfed. However, despite this family link the increased incidence in the breastfed group was still
clearly visible and significant. Finally,
in their multifactor analysis where they controlled for socioeconomic status, birth order, sheepskin use in infancy and the presence of
asthma, atopy or smoking in/by the
mother, all outcomes remained significant with the breastfed cohort again showing higher risk.
The authors were clearly surprised by the outcome of their study. They had anticipated exactly the opposite. To the best of their
knowledge and understanding, their study
is the most comprehensive and well-designed of all those examining the link between breastfeeding, asthma and atopy. They opine that
the reason some prior studies have
found the opposite result is due to the fact that the outcomes (asthma and atopy) are assessed at very early ages. For example, those
which test for asthma at age 2 or
less found evidence of protection, while theirs and others find increased risk at greater age.
The authors cite studies of Swedish, Californian, and Australian children who were breastfed had lower incidences of atopy at a young
age, and in Kenya breastfeeding was
related to a reduced severity of asthma, rather than incidence. A massive Brazilian study found lower rates of asthma in children
breastfed for more than six months than
those who were never breastfed. On the other hand, Tuscon, Italian and British children show that breastfeeding lead to increased risk
of atopy and asthma.
It is important to note that while some the studies mentioned in the previous two paragraphs were undeniably massive in their
undertaking, none can hold a torch to the
Lancet study discussed here. All previous studies confined themselves to cases where the children were, or were not, genetically
disposed to asthma and/or atopy. They
not attempt to control for smoking, the date of breast-feeding cessation, socioeconomic status and other factors. This study was
superbly designed and produced results
which are hard to deny.
To date the mechanism relating breastfeeding to asthma and atopy in children is poorly understood, which limits ability to make sense
of these contradictory results.
Without a causative mechanism, it is difficult to understand why one study produces one result while another produces something quite
different. A study5
examining infants in Estonia and Sweden, countries with low and high prevalences of atopy, respectivley, found that one year old
Estonian children had high densities of
Lactobacilli and eubacteria in their guts, while Swedish children had high densities of clostridia instead. Those childern with lower
lactobacilli densities and higher coliform
densities were more likely to develop allergies. Thus, breastfeeding might affect the balance of the bacteria in a child's gut, giving way
to future susceptibility to allergy.
Commentary and critique
When I first read about this story in the local newspaper, my reaction was two fold: first, this must have been paid for by a formula
company; second, their methodologies
must be totally skewed. To my surprise, upon reading the paper I found that this is not just solid science, but really good science. This
study was not paid for by any
multinational that I can find, and the authors seem to convey a real sense of discouragement (and excitement; they are scientists, after all!) at these findings.
state, as the last paragraph of their
Breastfeeding could be promoted for many reasons, including optimum nutrition and reduction of risk of infant infections. However, the
role of breastfeeding in protection
children against atopy and asthma cannot be supported on the basis of the present balance of evidence.
For those in the scientific community, the previous two sentences are as close to an emotional lament as you get.
I still think that breastfeeding should be encouraged and even pursued aggressively by the medical community, support groups and
federal/state policies. It is cheaper,
easier and better for the baby. However, it may not be the best nutritional course in every conceivable way. In the balance, by far
better than formula. However, be aware
that you might be increasing your child's risk of developing ashtma and/or allergies later in life.
1 Note that all of these findings, as well as the ones discussed in this write-up, are correlative and not causative. This
means we are implying or assuming
the existence of a pattern (A and B covary) is evidence that one causes the other (A causes B). See correlation is not causation for a good
explanation of this principle; in particular, the write-up by bitter_engineer.
2 Sears, Malcolm R., Justina M. Greene, Andrew R. Willan, D. Robin Taylor, Erin M. Flannery, Jan O. Cowan, G.
Peter Herbison and Richie Poulton.
relation between breastfeeding and development of atopy and asthma in children and young adults: a longitudinal study." 2002. The
Lancet. 360: 901-907.
3 Please be aware that I've added a space (" ") between "Type1&" and "c=Article" in this address so that the page
will format normally for anyone not blessed with a 23" CRT or an Apple TiTanium Powerbook.
4 Kramer, M. S. "Does breast feeding help protect against atopic disease? Biology, methodology and a golden
jubilee of controversy." 1988. The Journal of
Pediatrics. 112: 181-190.
5 Sepp, E., K. Julge, M. Vasar, P. Naaber, B. Bjorksten and M. Mikkelsaar. "Intestinal microflora of Estonian and
Swedish infants." 1997. Acta Pediatrica. 86: