King and her colleagues reported their findings in the American
Journal of Clinical Nutrition and other scientific publications.
King is now working on a follow-up study with pregnant volunteers aged
22-40 years. Each volunteer receives 15 milligrams of zinc from food
and supplements every day. Some volunteers receive prenatal iron supplements
of 65 milligrams a day.
King notes, "Some take their iron supplement in the morning, with
their breakfast, and others at bedtime, without a meal. We want to determine
whether zinc uptake is affected by taking the iron supplement at a particular
time of day and with or without a meal."
Concepcion Mendoza, a postdoctoral fellow in King's laboratory, is
leading this study. Fernando Viteri, a faculty member at the University
of California at Berkeley, is also a collaborator.
Studies in Brazil and South Korea are providing more information about
the interplay of zinc and iron or zinc and phytatea form of phosphorus.
Center scientists collaborated in these investigations.
"More than half of the people in the world don't get enough zinc,"
King points out. "In countries where grains or legumes such as
beans make up a significant component of the day's meals, zinc deficiency
is a special concern. That's because the zinc in grains and legumes
is less available to the body than the zinc in beef, pork, and dark-meat
The Brazilian experiment looked at the zinc used by 15 pregnant women
in Rio de Janeiro. The volunteers, aged 21-34, were given daily iron
supplements of 50 or 100 milligrams for most of the last half of pregnancy.
Volunteers ate their normal foods, including meats. Findings showed
that the 100-milligram iron supplements interfered with the uptake of
zinc but that the 50-milligram iron supplements did not.
Carmina L. Vargas Zapata and Carmen M. DonAngelo of the Federal University
of Rio de Janeiro conducted the research.
Zinc and Phytate Link Probed
A study in South Korea is exploring the interaction of phytate and
zinc in the body. Phytate is an essential nutrient. "The phytate
in grains such as rice and corn is thought to interfere with the uptake
and use of zinc," says Huang, a collaborator in the study.
Scientists are working with groups of female volunteersages 18-24
and 60-70. In the three-phase experiment, the researchers are altering
the relative amount of phytate to zinc the volunteers consume. In the
first phase, the women eat familiar fare, predominantly rice and vegetables.
This diet provides about 20 parts phytate to 1 part zinc.
In the second phase, the volunteers eat foods with less phytate, resulting
in a ratio of about 8 parts phytate to 1 part zinc. That's about the
ratio of phytate to zinc that Americans consume. The scientists lowered
the phytate consumption by providing white rice in place of higher phytate
For the third phase of the study, the volunteers eat their familiar
foods, including high-phytate rice. But they also take a 25-milligram
zinc supplement each day. This regimen again gives them a ratio of about
8 parts phytate to 1 part zinc.
Hee Young Paik of Seoul National University is directing the study
and providing blood samples from the volunteers to Huang, at her Davis
lab, for analysis of zinc transporters.
Is an mRNA-based Zinc Test Ahead?
Huang is looking at the levels of mRNAcreated from zinc transporter
genesin the samples. She wants to see which, if any, of the transporters
predict an individual's zinc uptake and use. If there is a correlation
between zinc use and the level of zinc transporter mRNA, the mRNA could
become the basis of a better test for the body's use of zinc.
She is also determining whether the levels of ZnT proteins vary with
age. "If there are significant differences in the way we process
zinc as we age," Huang says, "then the dietary allowance of
zinc may need to be adjusted."
Scientists have known for decades that zinc is essential for human
health. Foods that are good sources of zinc include beans, whole grains,
shellfish, red meat, and dark-meat poultry.By Marcia
Wood, Agricultural Research Service Information Staff.
This research is part of Human Nutrition, an ARS National Program
(#107) described on the World Wide Web at http://www.nps.ars.usda.gov.
Liping Huang and Janet
C. King are with the USDA-ARS Western
Human Nutrition Research Center, One Shields Ave., Davis, CA 95616;
phone (530) 754-5756, fax (530) 754-6015 [Huang], phone (530) 752-5268,
fax (530) 752-5271 [King].