Recipient Organization
CHILDREN'S HOSPITAL OAKLAND RESEARCH INSTITUTE
5700 MARTIN LUTHER KING, JR. WAY
OAKLAND,CA 94609
Performing Department
(N/A)
Non Technical Summary
13 percent of the U.S. population is elderly individuals over 65 years of age. They are the most rapidly growing population segment in the United States. National surveys show that their dietary zinc intakes are inadequate and that many of their health problems are conditions associated with poor zinc nutriture. As the elderly population grows, demands for health services will be increased by their health problems. Improved nutrition, especially zinc, could reduce some of those problems. Age-specific standards for zinc intake are essential to establish policies and programs to improve their zinc nutriture. However, dietary zinc requirements of the elderly have never been studied systematically. This gap must be addressed in order to assure that nutrition policies and feeding programs meet the zinc needs of this important population. In this study, we will complete a comprehensive study of the dietary zinc requirement of individuals over 70 years of age using data from
individuals fed typical mixed diets.
Animal Health Component
75%
Research Effort Categories
Basic
25%
Applied
75%
Developmental
(N/A)
Goals / Objectives
To measure endogenous fecal zinc (EFZ) losses, urinary zinc, fractional zinc absorption (FZA), and total absorbable zinc in 12 men and 12 women over 70 years of age when fed three different levels of dietary zinc including the Estimated Average Requirement (EAR), 40 percent less than the EAR, and 40 percent above the EAR. To derive an estimate of an EAR for elderly men and for elderly women using data from individuals in DRI model and to calculate the EARs coefficient of variation and determine if variation in EFZ or FZA is related to fat-free mass, resting metabolic rates, enzymatic markers of liver function, biochemical markers of subclinical infection, or glomerular filtration rates. To evaluate the effect of changes in dietary zinc on the expression of cellular zinc transporter genes in elderly men and women fed diets ranging from 40 percent below to 40 percent above their EAR and to determine if there is a relationship between zinc transporter gene expression and
endogenous zinc loss or absorption.
Project Methods
Our overall goal is to determine the dietary zinc requirements of the elderly and to define the relationship between cellular zinc transporter gene expression and measurements of whole body zinc homeostasis. Twelve men and 12 women over 70 years of age will participate in zinc metabolic studies to measure EFZ, urinary zinc, FZA, and total absorbed zinc using stable isotopes. Each participant will be fed three different levels of dietary zinc: the 2002 EAR, 40 percent less than the EAR, and 40 percent greater than the EAR. The women will be fed diets ranging from 4.1 to 9.5 mg per day; men will be fed intakes from 5.6 to 13.2 mg per day. These levels were chosen because they represent a range of typical zinc intakes from habitual diets by this population. For example, the median zinc intakes of elderly women in NHANES III ranged from 6.6 to 7.2; the range for men was 8.8 to 10.3. The participants will be adapted to each diet for seven days at home before entering the
GCRC at San Francisco General Hospital (SFGH) for a week to conduct the metabolic studies. In addition to measuring zinc absorption, endogenous fecal, and urinary zinc losses, we will measure zinc balance, plasma zinc, the size and turnover of the exchangeable zinc pool (EZP), and cellular zinc transporter gene expression. We will also measure body composition, resting metabolic rates, enzymatic markers of liver function, biochemical markers of subclinical infection, and glomerular filtration rates to assess the possible effect of these physiological parameters on our measures of zinc homeostasis. After a 4 week wash-out period, while the participants consume their usual diets at home, a two-week study of the second diet will begin, and the third diet will be administered after a 4-week wash-out period. Thus, each participant will be studied for three 2-week periods over a 14-week period. The three dietary treatments will be administered randomly. Previous work in our laboratory has
shown that a 4-week wash-out period is sufficient to reduce isotopic zinc enrichments in plasma, urine, and stools to natural abundance levels. However, a baseline urine and fecal sample is collected at the beginning of every metabolic period to determine background isotope levels.