Fellow lactnetters, I wrote to Patty Stuart-Macadam and shared with her the
gist of the post to LactNet about "Diet, Demography, and Disease" and asked
if she would like to respond, since this issue of iron levels in infants
comes up frequently.  Here is her reply:
>
>       Yes - I would like to reply by quoting from someone who says it
>better than I do.  This is from a wonderful book called Evolution and
>Healing: The New Science of Darwinian Medicine by R.M. Nesse and G.C.
>Williams, 1994 p 29-31:
>
>         Iron Withholding
>
>       Our bodies have a related defense mechanism, of which most people
>are unaware and which physicians sometimes unwittingly attempt to
>frustrate.  Here are some clues about how it works.  A patient with
>chronic tuberculosis is found to have a low level of iron in his blood.
>A physician concludes that correcting the anemia may increase the
>patient's resistance, so she gives him an iron supplement.  The patient's
>infection gets worse.  Another clue: Zulu men often drink beer made in
>iron pots and often get serious liver infections caused by an amoeba.  In
>contrast, less than 10 percent of Masai tribesmen have amoebic
>infections.  They are herdsmen and drink large amounts of milk.  When a
>group of Masai were given iron supplements, 88 percent soon got an
>amoebic infection.  In another study, well-meaning investigators gave
>iron to supplement the low levels found in Somali nomads.  At the end of
>one month, 38 percent had infections versus 8 percent of those who had
>not taken the supplements.
>       Yet another clue: eggs are a rich source of nutrients, but their
>porous shells can be readily penetrated by bacteria.  So how can eggs
>stay fresh so long?  They contain lots of iron, but it is all in the
>yolk, none in the surrounding white.  Egg white protein is 12 percent
>conalbumin, a  molecule whose structure tightly binds iron and therby
>withholds it from any bacteria that might get in.  Prior to the
>antibiotic era, egg whites were used to treat infections.
>       The protein in human milk is 20 percent lactoferrin, another
>molecule designed to bind iron.  Cow's milk has only about 2
>percentlactoferrin, and breast-fed vbabies consequently have fewer
>infections
>than those fed from bottles.  Lactoferrin is also concentrated in tears
>and saliva and especially at wounds, where an elevated acidity makes it
>especially efficient in binding iron.  The researchers who discovered
>conalbumin predicted that there should be a similar molecule to bind iron
>within the body.  This led to the discovery of transferrin, another
>protein that binds iron tightly.  Transferrin releases iron only to cells
>that carry special recognition markers.  Bacteria lack the needed code
>and can't get the iron.  People suffering from protein deprivation may
>have levels of transferrin less than 10 percent of normal.  If they
>receive iron supplements before the body has time to rebuild its supply
>of transferrin, free iron in the blood makes fatal infections likely - as
>has been a tragic outcome of some attempts to relieve victims of famine.
>       By now the nature of this defense is surely obvious.  Iron is a
>crucial and scarce resource for bacteria, and their hosts have evolved a
>wide variety of mechanisms to keep them from getting it.  In the presence
>of infection, the body releases a chemical called leukocyte endogenous
>mediator (LEM), which both raises body temperature and greatly decreases
>the availability of iron in the blood.  Iron absorption by the gut is
>also decreased during infection.  Even our food preferences change.  In
>the midst of a bout of influenza, such iron-rich foods as ham and eggs
>suddenly seem disgusting; we prefer tea and toast.  This is just the
>ticket for keeping iron away from pathogens.  We tend now to think of
>bloodletting as an example of early medical ignorance, but perhaps, as
>Kluger has suggested, it did help some patients by lowering their iron
>levels.
>       It became clear in the 1970s that low iron levels associated with
>disease could be helpful, not harmful, but even now, Kluger and his
>associates find that only 11 percent of physicians and 6 percent of
>pharmacists know iron supplementation may harm patients who have
>infections.  Even top researchers may neglect to mention this adaptive
>mechanism.  A recent study in the New England Journal of Medicine showed
>that children with cerebral malaria were more likely to revover if they
>were treated with a chemical that binds iron, but the article did not
>describe
>the body's natural system for binding iron during infection.  The evolved
>mechanism that regulates iron binding is but one specific illustration of
>the broader principle that we should be careful to distinguish defenses
>from other manifestations of infection, slow to conclude that a bodily
>response is maladaptive, and cautious about overriding defensive
>responses.  In short, we should respect the evolved wisdom of the body.


Patricia Stuart-Macadam, Ph.D.
Professor of Anthropology
University of Toronto
----------------------------------------------------------------------------
-------
Katherine A. Dettwyler, Ph.D.                         email: [log in to unmask]
Anthropology Department                               phone: (409) 845-5256
Texas A&M University                                    fax: (409) 845-4070
College Station, TX  77843-4352