This is an excerpt from my manuscript "Evolutionary Medicine and
Breastfeeding," under review at the journal "Social Science and Medicine."
It can be reprinted as long as you include my name and affiliation, and
indicate where it came from.


"At the same time, however, it is clear from the medical research that the
longer a child is breastfed, the better the health outcome for that child,
even under the best of First World conditions.  Only a few studies have
defined breast milk intake as a dose-response variable (Fredrickson, 1995),
and looked at the effect of varying durations of breastfeeding on child
health.  Most studies define infant feeding as either breast or bottle, with
the breastfeeding group getting breast milk for varying lengths of time.
Some have used six-month interval categories, and examined health outcomes
for children "not breastfed," "breastfed for 0-6 months," "breastfed for
6-12 months," "breastfed for 12-18 months," and "breastfed for 18-24 months
or longer."  In every case, whatever the outcome health variable, when
duration of breastfeeding was considered, the longer the child was
breastfed, the lower the risk for the adverse health outcome.  These results
hold true for studies on malocclusion (Labbok and Hendershot, 1987),
gastrointestinal disease (Howie et al., 1990), Sudden Infant Death Syndrome
(Fredrickson et al., 1993; Mitchell et al., 1991), otitis media (Duncan et
al., 1993), childhood cancer (Davis et al., 1988; Golding et al., 1990) and
juvenile diabetes (Cavallo et al., 1996; Dahl-Jørgensen et al., 1991; Mayer
et al., 1988; Virtanen et al., 1991).  Likewise, the research on the
relationship between cognitive achievement (IQ scores, grades in school)
showed the greatest gains for those children breastfed the longest.  To put
it another way (Wiessinger, 1996), the research showed that the shorter the
duration of breastfeeding, the greater the cognitive deficits (Rogan and
Gladen, 1993).

Recent research also suggests that many health problems of adults can be
traced to lack of breastfeeding or short durations of breastfeeding,
suggesting that while children raised on formula may survive, they do not
necessarily thrive as adults.  Premature weaning has been identified as a
factor in all of the following diseases or conditions: inflammatory bowel
disease (Acheson and Truelove, 1961), Crohn's disease (Koletzko et al.,
1989), celiac disease (Greco et al., 1988), Schönlein-Henoch purpura
(Pisacane et al., 1992), breast cancer (Freudenheim et al., 1994), multiple
sclerosis (Pisacane et al., 1994), allergies (many studies, reviewed in
Cunningham, 1995), chronic respiratory diseases (also reviewed in
Cunningham, 1995), and coronary artery disease (Fall et al., 1992; Kato et
al., 1992; Kawasaki et al., 1974; Marmot et al., 1980; Osborn, 1968).

At this point in scientific understanding, no research is available that
looks at the differentials in disease and cognitive outcomes for children
breastfed longer than two years, compared with those breastfed for shorter
periods.  All of the studies that have examined the relationship between
duration of breastfeeding and health outcomes stop with an upper category of
24+ months.  No studies have compared the health differential between
children breastfed for three years compared with those breastfed for four
years, compared with those breastfed for five years, and so on.  Thus,
stating unequivocally that there are significant or substantial health
benefits to breastfeeding beyond two years of age is impossible.  At the
same time, stating unequivocally that there are not significant or
substantial health benefits to breastfeeding beyond two years of age is
impossible.  The additional health benefits, in a First World setting, of
breastfeeding beyond two years may be very slight, or they may be
significant; they may affect health in childhood, or they may not become
apparent until middle-age or later--the data are simply not available at
this time.  Thus, health care professionals cannot guarantee mothers that
continued breastfeeding will result in noticeable improvements in lifelong
health or longevity for their children.

What is more significant, and clear, is that health care professionals have
no basis for claiming that the health benefits of breastfeeding ever cease
or become insignificant, nor for claiming that extended breastfeeding ever
harms a child or is contraindicated after a certain age.  All of the
research shows better health outcomes the longer the child breastfeeds, up
to the current study limits of 24 months.  If the mother and child want to
continue breastfeeding, no reasons exist to suggest that they should not.
In particular, no reasons exist to question the motivations of the mother
who wants to give her child the best possible lifelong health, nor to accuse
her of harboring ulterior motives for continuing to breastfeed well beyond
two years.

Undoubtedly, in terms of health outcomes, the first year of breastfeeding is
more important than the fourth year.  The first month is more important than
the 24th month.  The first week is more important than the 52nd week.  "Any
breastfeeding," as a research category, has been shown to result in
significant health improvements compared with children in the "no
breastfeeding" category.  No evidence exists to suggest that the health
benefits ever cease, nor that the cost/benefit ratio ever becomes so high as
to make continued breastfeeding pointless or contraindicated.  Future
research may confirm that breastfeeding for the full length of time normal
for our species, in evolutionary and physiological terms, may result in
children who thrive--in terms of physical health, cognitive development, and
emotional stability--compared with children who were weaned prematurely."

© Katherine A. Dettwyler 1997 All rights reserved.
Katherine A. Dettwyler, Ph.D.
Texas A&M University