A Close Look
at Milk and Iron Uptake
By Luis Pons
July 15, 2004
In studies that may one day impact food
crops, an Agricultural Research Service
scientist and colleagues have examined the mechanisms by which iron in milk is
absorbed by the human body.
Milk is not high in iron content. But animal physiologist Ray Glahn of the
ARS U.S. Plant, Soil and
Nutrition Research Laboratory in Ithaca, N.Y., and cooperators have used a
combination of human cell culture and separation techniques to reveal clues
about the bioavailability of the iron that is there. They especially wanted to
know how that bioavailability was affected by fat, whey and casein, three major
components of both human milk and cow's milk.
Glahn is working with Paz Etcheverry, now a postdoctoral associate at
Baylor College of Medicine in Houston, Texas,
and professor Dennis D. Miller of Cornell
University's Department of Food
To no one's surprise, the study found that there appear to be some compounds
in human milk that promote iron uptake. According to Glahn, identifying these
compounds and gaining understanding toward how they work may enable researchers
to make other foods, such as staple food crops, more nutritious.
Noteworthy, however, was that one of the facilitating factors was not
lactoferrin. For years, scientists have debated whether that protein's ability
to bind and transport iron--and release it at specific receptor cells in the
human intestine--actually enhances iron absorption.
Instead, the study found that it's the low-molecular-weight fractions of
whey that promote uptake.
Overall, the study showed that removal of whey from human milk resulted in
less iron uptake. Removal of the fat fraction increased iron uptake, indicating
that this component hinders iron bioavailability. Removal of the casein
component had no effect.
In cow's milk, the story was different. Removal of whey and fat had no
effect on iron uptake, while removal of the casein fraction increased uptake,
indicating that casein is an iron-uptake inhibitor in cow's milk.
more about these findings in the July issue of Agricultural Research
ARS is the U.S. Department of
Agriculture's chief scientific research agency.