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American Journal of Clinical Nutrition, Vol. 87, No. 5, 1224-1229, May 2008
© 2008 American Society for Nutrition

ORIGINAL RESEARCH COMMUNICATION

Current dietary zinc intake has a greater effect on fractional zinc absorption than does longer term zinc consumption in healthy adult men 1,2,3

Carolyn S Chung, Jodi Stookey, Doris Dare, Ross Welch, Tuan Q Nguyen, Raimund Roehl, Janet M Peerson, Janet C King and Kenneth H Brown

1 From the Program in International and Community Nutrition and the Department of Nutrition, University of California, Davis, CA (JMP, JCK, and KHB); Children's Hospital of Oakland Research Institute, Oakland, CA (CSC, JS, TQN, and JCK); General Clinical Research Center (GCRC), University of California, San Francisco, CA (DD); United States Department of Agriculture, Agricultural Research Service, Cornell University, Ithaca, NY (RW); and the California Department of Public Health, Sanitation and Radiation Laboratory, Richmond, CA (RR)

2 Supported, in part, by beef and veal producers and importers through their $1-per-head checkoff and was produced for the Cattlemen's Beef Board and state beef councils by the National Cattlemen's Beef Association, by the General Clinical Research Center, University of California, San Francisco at the San Francisco General Hospital, and by the National Center for Research Resources, National Institutes of Health (grant MO1-RR00083-43)

3 Reprints not available. Address correspondence to KH Brown, Program in International and Community Nutrition and Department of Nutrition, University of California, Davis, One Shields Avenue, Davis, CA 95616. E-mail: khbrown{at}ucdavis.edu.


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Background: No studies have examined the independent effects of current and longer-term dietary zinc intakes on zinc absorption.

Objective: We determined the effects of current compared with longer-term zinc intake on fractional zinc absorption (FZA).

Design: We studied 9 men whose usual zinc intakes were >11 mg/d. FZA was measured at baseline, depletion (0.6 mg Zn/d for 1 wk and 4 mg Zn/d for 5 wk), and repletion (11 mg Zn/d for 4 wk with 20 mg supplemental Zn/d for first 7 d). During 2 successive days after each dietary period, subjects consumed either adequate-zinc meals (11 mg Zn/d) with a zinc stable isotope tracer for 1 d, followed by low-zinc meals (4 mg Zn/d) with zinc tracer, or vice versa. Five days after oral dosing, a zinc tracer was infused intravenously. FZA was measured with the use of a modified double isotope tracer ratio method with urine samples collected on days 5–7 and 10–12 of absorption studies.

Results: Plasma and urinary zinc did not vary by dietary period. Mean FZA was greater from low-zinc meals than from adequate-zinc meals (60.9% ± 13.8% compared with 36.1% ± 8.9%; P < 0.0001), whereas mean total absorbed zinc was greater from adequate-zinc meals than from low-zinc meals (3.60 ± 0.91 compared with 2.48 ± 0.56; P < 0.0001), regardless of the longer-term dietary period.

Conclusions: FZA was inversely related to current zinc intake, but there was no detectable effect of longer-term dietary zinc. If longer- term zinc intake does modify FZA, such changes are smaller than those caused by current zinc intake, or they occur only after more severe zinc depletion.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
The amount of zinc in a meal was reported to influence zinc absorption (1, 2). In particular, fractional zinc absorption (FZA) declines as the amount of zinc increases in the meal. Some researchers have also suggested that longer-term zinc intakes, hence the zinc status of the person, may affect FZA (3-6). However, the studies that were used to support this claim were confounded because the zinc-depleted subjects were consuming low-zinc diets during the studies of zinc absorption, so the zinc intake may have affected FZA independently of the subjects' zinc status. To our knowledge, there are no studies that examined simultaneously the independent effects of current and longer- term dietary zinc intakes on zinc absorption. Therefore, the objective of the present study was to compare the effects of current compared with longer-term intakes of dietary zinc on FZA from a controlled, mixed diet. This information can be used to improve estimates of dietary zinc requirements. Because of the difficulty in assessing individual zinc status, we examined the effects of varying the intakes of dietary zinc for periods of 4–6 wk on the subjects' zinc absorption instead of relying only on measures of zinc status.


   SUBJECTS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Subjects
Healthy men aged 19–50 y were recruited from the Davis and San Francisco areas. Men with plasma zinc concentrations > 74 µg/dL (7) and dietary zinc intakes ≥ 11 mg/d, the recommended dietary allowance for men (8), were considered to have adequate zinc status and thus were invited to participate in the study. Dietary zinc intakes before enrollment into the study were assessed with the average of 5 nonconsecutive, 24-h dietary recalls, including 1 weekend day, during a period of 2 wk, and were analyzed with the use of FOOD PROCESSOR SQL software (ESHA Research, Salem, OR). Volunteers were excluded from the study if they reported any chronic diseases, smoking, or alcohol abuse; use of illicit drugs; regular consumption of medications, zinc supplements, or both; or consuming zinc supplements 4 wk before entering the study.

The study was approved by the Institutional Review Boards of the University of California, Davis, the Children's Hospital and Research Center of Oakland, and the University of California, San Francisco (UCSF). Written informed consent was obtained from each subject. The clinical phase of the study was conducted at 2 sites: the General Clinical Research Center (GCRC) at the San Francisco General Hospital, UCSF, and the Ragle Human Nutrition Research Center at the University of California, Davis. Subjects followed either a free-living protocol in which they consumed lunch meals at the GCRC in San Francisco or at the Ragle Center in Davis during weekdays (breakfast and dinner and weekend meals were provided for self-administered, home consumption; n = 6) or an inpatient protocol in which they consumed all meals and stayed at the GCRC for the study duration (n = 3).

Study design
The study was a crossover dietary intervention of 2 intakes of zinc (11 mg Zn/d and 4 mg Zn/d) to modify zinc status during 3 sequential longer-term dietary zinc periods (Figure 1Go). At the end of each longer-term dietary zinc period, zinc absorption was measured from 2 sets of test meals, which provided either adequate (11 mg Zn/d) or low (4 mg Zn/d) amounts of zinc. Zinc absorption from the test meals was measured with a modified dual isotope tracer ratio method on 2 consecutive days in varied order, as explained below. Fasting plasma zinc concentration and 24-h urinary zinc excretion were also assessed at the end of each dietary period.


Figure 1
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  		FIGURE 1.. Study design: adequate- and low-zinc longer-term dietary periods (DPs). {dagger}Subjects were supplemented with 1.3 g phytic acid on days 14–34. {ddagger}Subjects were supplemented with 20 mg Zn as zinc gluconate (ZnG) on days 56–64.

 
During the 13-d baseline diet period (diet period 1), the subjects consumed the adequate zinc diet that provided 11 mg Zn/d (Figure 1Go). During the subsequent 42-d longer-term dietary zinc period (diet period 2), the subjects consumed a liquid diet that provided 0.6 mg Zn/d for 7 d followed by a low-zinc mixed diet that provided 4 mg Zn/d for 35 d to deplete their zinc status. We used a slight modification of the protocol described previously by Ruz et al (9). Phytate (1.3 g/d from corn; Sigma, St Louis, MO) was added to the liquid diet and beverages in the mixed diet and were distributed to all meals for the first 21 d of dietary period 2 to reduce zinc absorption. During the next 28-d period (diet period 3), the subjects consumed the adequate-zinc diet that provided 11 mg Zn/d and was supplemented with 20 mg zinc as zinc gluconate/d for the first 7 d (a 10-mg tablet before breakfast and before dinner) to replete their zinc status. The subjects consumed a daily multiple vitamin supplement without minerals (Longs Vitamins One Daily Multiple Vitamins; Long's Pharmacy, Oakland, CA) on entry into and throughout the study, except on days when oral zinc stable isotopes were administered. The multiple vitamin supplement contained vitamins A, C, D, and E and all B vitamins.

Diets
Both the adequate-zinc diet (11 mg/d) and the low-zinc diet (4 mg/d) provided {approx}2500 kcal (55% of energy from carbohydrate, 15% of energy from protein, and 30% of energy from fat). The volunteers' actual energy requirements were based on the Harris-Benedict equation for basal energy expenditure (10), and an assumed activity factor of 1.5. Energy intakes were adjusted by adding zinc-free energy shakes composed of nondairy creamer, egg albumin, and flavored drink mix (Kool-Aid; Kraft Foods, Northfield, IL) in 200-kcal increments to maintain a constant body weight. Total energy intakes ranged from 2461 kcal to 3100 kcal, with a mean ± SD of 2838 ± 221 kcal.

Adequate-zinc diets contained beef as their main source of zinc and protein. Low-zinc diets contained chicken as their main source of protein. Both diets were matched for protein amount from animal sources and had a phytate-to-zinc molar ratio of {approx}10. Macronutrient contents of the study diets were estimated by FOOD PROCESSOR PRO software (ESHA Food Pro SQL v 9.6, Salem, OR) (Table 1Go). Meals were served 3 times daily at 0830, 1200, and 1730. Subjects were permitted to add salt and pepper to meals and to consume tap water ad libitum. Methylcellulose (2–4 g; Sigma Chemical) was added to the maintenance diets to ensure regular bowel movements, except during absorption study days.


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  		TABLE 1. Nutrient content of adequate- and low-zinc diets for absorption studies

 
The total daily intakes of zinc and phytate were distributed equally across the 3 meals. Diets were measured for zinc and phytate contents. Duplicate portions of all of the meals for each day were blended into homogenized, whole-day composites. Aliquots of the homogenized diets were digested in concentrated nitric acid with the use of microwave digestion (MARS 5; CEM Corp, Matthews, NC) and were then diluted for analysis along with appropriate internal standards. Dietary zinc concentrations were measured with the use of inductively coupled plasma optical emission spectrophotometry (ICP-OES; Varian Vista Pro, Palo Alto, CA), and phytate concentrations amounts in the study diets and test meals were measured by HPLC with the use of a Dionex Liquid Chromatograph System (Dionex Corp, Sunnyvale, CA) at the US Department of Agriculture, Agricultural Research Service at Cornell University, Ithaca, NY. A 4-d cycle of the adequate-zinc diet and a 5-d cycle of the low-zinc diet were developed for the longer-term dietary periods. Examples of 1 d of each of the mixed diets are shown in Table 2Go; these are also the diets that were used for all the studies of zinc absorption. The diets were prepared by the dietetic staff of the metabolic kitchens of the UCSF GCRC at the San Francisco General Hospital and the Ragle Human Nutrition Research Center at the University of California, Davis.


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  		TABLE 2. Adequate- and low-zinc diets for absorption studies

 
Stable isotopes
Highly enriched stable isotopic tracers, 67Zntr (88.6% enriched with 67Zn) and 70Zntr (88.5% enriched with 70Zn) as zinc oxide (Trace Sciences International Corp, Ontario, Canada), were dissolved in concentrated hydrochloric acid (Optima; Fisher, Pittsburgh, PA; 3 µL HCl/mg ZnO). The solutions were then diluted with triply deionized water to a final concentration of 1.6 mg 67Zntr/mL or 0.5 mg 70Zntr/mL and filtered through a 0.22-µm filter unit (Millipore Products Division, Bedford, MA). The solution for intravenous use was sterilized and tested for sterility and pyrogenicity by the School of Pharmacy, UCSF. Intravenous doses (1.0 mL) that provided 0.5 mg 70Zntr were stored in individually sealed, sterile vials until used. The amounts of administered oral and intravenous tracer doses were calculated from the total zinc concentration of the solutions, which was measured by with the use of ICP-OES (Varian Vista Pro) and the weight of the administered dose.

Absorption studies
FZA was measured with the use of a modification of the double isotopic tracer technique (11, 12) during the last 13 d of the 3 longer-term dietary zinc periods (Figure 1Go). All of the absorption studies were conducted at the GCRC, and the subjects remained in the research ward during the first 72 h of each absorption study. For each study, the subjects received the adequate-zinc diet for 1 d followed by the low-zinc diet on the subsequent day, or vice versa (Figure 2Go). Oral zinc stable isotopes were administered in aqueous solution and consumed immediately at the end of each meal. The amount of isotope given equaled 10% of the day's dietary zinc intake and was distributed equally over the 3 meals. In other words, 1.1 mg 67Zntr/d was given with the adequate zinc test meals providing 9.9 mg Zn, for a total intake of 11 mg Zn/d; and 0.4 mg 70Zntr/d was given with the low zinc test meals providing 3.6 mg Zn/d, for a total of 4 mg Zn/d. The vials with the oral stable isotopic tracer solution were rinsed 3 times with water, and the rinse water was also consumed. On the morning of absorption study day 7, an in-dwelling catheter was used to infuse 0.5 mg 70Zntr (1.0 mL) over 1–2 min into the antecubital vein of the subject's arm. The catheter tubing was then flushed with 3 mL sterile saline to ensure that the entire tracer dose was infused. The exact amount of tracer solution infused was determined by weighing the syringe that contained the tracer before and after the infusion. Samples from the second urinary void were collected on the morning of absorption study days 5–7 and 10–12 to measure zinc isotopic ratios. Fasting blood samples were taken on days 1 and 13 of each absorption study period, and a 24-h urine collection was obtained on day 13 of each absorption study period.


Figure 2
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  		FIGURE 2.. Protocol for zinc absorption studies using zinc stable isotope tracers. {dagger}1st Oral Zntr: 0.4 mg 70Zntr used to trace low-zinc diet. {ddagger}2nd Oral Zntr: 1.1 mg 67Zntr used to trace adequate-zinc diet. °The order of these 2 test diets varied at the end of each longer-term dietary period, as explained in the text. *IV 70Zntr: intravenous 0.5 mg Zn as ZnCl2.

 
Sample analyses
Blood samples were centrifuged for 10 min at 4 °C and 2000 x g immediately after being drawn. Urine samples were weighed, and aliquots were acidified with 400 µL HCl (trace metal grade; Fisher, Fairlawn, NJ)/100 mL urine. Plasma and urine were divided into aliquots and stored at –20 °C until analyzed for zinc with ICP-OES (Varian Vista Pro). Markers of oxidative stress, DNA damage, and gene expression profiles from whole blood were measured at 4 time points throughout the study and will be reported elsewhere.

Procedures used to prepare and measure urine samples for zinc isotopic ratios were the same as previously reported (11). Briefly, urine samples were adjusted to pH 5.3 and applied to a chelating resin (Chelex 100; Bio-Rad, Hercules, CA) to eliminate macrominerals. Samples were then purified by ion-exchange chromatography (AG1-X8; Bio-Rad). Pure zinc was eluted with 0.0005 N HCl, evaporated to dryness, and redissolved in 1% HNO3 to provide a concentration of 0.5 mg/g, or 0.5 ppm, for inductively coupled plasma mass spectrometric (ICP-MS) analysis. Purified samples were then analyzed for urinary isotopic ratios (67Zn to 66Zn and 70Zn to 66Zn) by ICP-MS (ELAN 6000 ICP-MS; Perkin Elmer, Norwalk, CT). The isotopic ratios were then converted to tracer-to-tracee ratios (TTRs), as previously described (12). TTR data for samples highly enriched in 67Zn and 70Zn are defined as 67ZnTTR and 70ZnTTR, respectively.

FZA was measured by a modification of the double isotope tracer ratio (DITR) method, as previously described (13, 14). The standard DITR method measures FZA by using zinc isotopic ratios in single urine samples obtained 3, 4, and 5 d after administering oral and intravenous tracers. The modified DITR technique for FZA (15) was implemented by using the SAAM II computer program (version 1.2; SAAM Institute, Seattle, WA) to develop individual exponential equations describing regression lines that were fitted simultaneously to semi-log plots of urine 67ZnTTR and 70ZnTTR data by day of study. The model was subjected to the constraint that the exponential components, ie, slopes of the simple regression lines of fitted TTR data, are equal. The intercepts, denoted as 67IntTTR and 70IntTTR, of the 3 slopes (2 oral and 1 intravenous) estimated by the SAAM model were used to calculate FZA, after allowing for different times of administration: FZA = [67IntTTR (oral)/70IntTTR (intravenous)] x [intravenous dose 70Zntr/oral dose 67Zntr]. The 70Zntr given intravenously was corrected for background 70Zntr consumed as the oral tracer 7 d earlier. Total absorbed zinc (TAZ) was calculated by multiplying FZA by the total amount of zinc ingested.

Sample size estimate and statistical analysis
Originally, we planned to enroll 16 subjects, which, according to previous work (6, 16), would have permitted detection of a within-subject difference in FZA of 0.05 between zinc intakes from the test meals and of 0.06 among the 3 longer-term dietary zinc periods (ie, in relation to presumed zinc status), both with 80% power and a level of significance of 0.05. On the basis of the actual sample size of 9 men and the observed variation in FZA, we were able to detect a within-subject difference in FZA of 0.08 by zinc intake from the test meals and of 0.10 by longer-term dietary zinc periods, with 80% power and a 5% chance of a type I error.

Repeated-measures analysis of variance was used to compare differences in FZA and TAZ by current zinc intake and longer- term dietary zinc period, controlling for the order in which test meals were given in each of the absorption studies (SAS for WINDOWS, version 9; SAS Institute, Cary, NC). The PROC GLM model included main effects (current zinc intake, longer- term dietary zinc period, and order in which test meals were given) and their interaction terms and random effects (the interactions between main effects and subjects). Differences in plasma and urinary zinc concentrations at the end of each longer- term dietary zinc period were assessed with the use of repeated-measures analysis of variance and paired Student's t tests. Pairwise significant differences were assessed with the use of Tukey's test for multiple comparisons. Correlations between plasma zinc concentrations and urinary zinc excretion with FZA and TAZ were also determined. Values were considered significant at P < 0.05.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
The characteristics of the 9 male subjects are summarized in Table 3Go. The subjects' body mass index (in kg/m2) ranged from 20.8 to 25.9, and they all reported usual zinc intakes > 11 mg/d before the study.


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  		TABLE 3. Subject characteristics at the start of the study (n = 9)1

 
The initial fasting plasma zinc concentrations were >74 µg/dL, and none of the men were anemic (hemoglobin: >13 g/dL). The general health of the men remained good throughout the study; hemoglobin (13–18 g/dL), hematocrit (40–52%), and white blood cell counts (4–12 x 103 cells/µL) assessed at each absorption study were within normal limits. Mean body weight did not change significantly throughout the study.

Plasma and urinary zinc concentrations measured at the end of each longer-term dietary zinc period did not differ (Figure 3Go). However, plasma zinc concentrations were 10% lower than baseline on day 21 (P = 0.03) after the 7 d of severely low-zinc intake (0.6 mg Zn/d) and 13% higher at the end of the study (day 83; P = 0.02) compared with the end of the low zinc dietary period on day 56.


Figure 3
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  		FIGURE 3.. Mean (±SD) plasma zinc concentration (•) and urinary zinc excretion ({blacksquare}) by diet period (DP) (n = 9). {ddagger}Shading indicates low-zinc DP. *Plasma zinc concentrations were significantly different on day 21 compared with the end of the adequate zinc DP (day 13) and on day 83 compared with the end of the low-zinc DP (day 56) (P < 0.05, Tukey's test).

 
FZA and TAZ from the adequate and low zinc test meals were significantly related to current zinc intakes, regardless of dietary period (Table 4Go). The average FZA from the low zinc test meals was 69% greater than FZA from the adequate zinc test meals when the results of all 3 longer-term dietary periods were combined (P < 0.0001). However, the average TAZ from the adequate zinc test meals was 45% greater than that from the low zinc test meals (P < 0.0001).


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  		TABLE 4. Fractional zinc absorption (FZA) and total absorbed zinc (TAZ) from adequate-and low-zinc test meals during longer-term periods of adequate- and low-zinc intakes1

 
FZA (P = 0.17) and TAZ (P = 0.37) from the adequate or low zinc test meals did not differ significantly by longer-term dietary zinc period or by the order in which the test meals were given (FZA: P = 0.75; TAZ: P = 0.81). Mean plasma zinc concentrations and total urinary zinc were not correlated with FZA and TAZ across or within subjects.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
The results of these tracer studies of zinc absorption, carried out under carefully controlled dietary conditions, indicate that the current intake of dietary zinc had a strong negative relation with FZA and positive relation with TAZ, whereas the longer- term zinc consumption had no detectable effect on FZA and TAZ. In particular, FZA was 69% greater when the subjects consumed 4 mg Zn/d than when they consumed 11 mg Zn/d, regardless of the order of the absorption test study diets or the longer-term dietary zinc intakes during the weeks before the absorption tests. However, TAZ was 45% greater when subjects consumed 11 mg Zn/d than when they consumed 4 mg Zn/d.

These results for the effect of current dietary zinc intake on the efficiency of zinc absorption are consistent with the findings of several previous studies. For example, in a study conducted in adult volunteers, the efficiency of zinc absorption decreased from 73% to 46% as the meal zinc content was increased from 2.6 mg to 13.1 mg (1). Likewise, in a study conducted in children the FZA decreased progressively from 34% to 24% and 13%, as zinc intakes rose from 2 to 5 and 10 mg Zn/d, respectively (2). However, the total amount of zinc that was absorbed by the subjects in both those studies increased in relation to zinc intake, as was seen in the current study.

Our observation about the lack of detectable effect of longer- term dietary zinc intake on the efficiency of zinc absorption is remarkable because previous studies have suggested that FZA may vary according to a person's zinc status (3-6). In these studies, zinc-depleted subjects absorbed a higher fraction of dietary zinc than when they had adequate zinc status. However, in each of these cases, the possible effects of the longer-term zinc intake and zinc status were confounded by the likely effect of current zinc intake. Because the assessments of zinc absorption during those earlier studies were completed by using the same low zinc test diets that were used to induce zinc depletion in the study subjects, it is conceivable that the higher FZAs that were observed were due to the low zinc intake during the absorption tests rather than the effects of longer-term low zinc intake and resulting depletion of zinc status. The present study addressed confounding factors in the aforementioned studies by measuring zinc absorption from test diets providing either low or adequate amounts of zinc on subsequent days and matching the diets for phytate-to-zinc molar ratios and amounts of animal protein.

Possible explanations for the lack of any detectable effect of longer-term zinc intake on zinc absorption in the present study are that a person's zinc status does not influence zinc absorption or that the subjects were not, in fact, zinc depleted, so there was insufficient stimulus for them to increase zinc absorption. It is also possible that there was inadequate statistical power to detect such an effect. The current study protocol used the same dietary regimen that was reported previously to induce zinc depletion in adult male Chilean volunteers, as evidenced by decreases in their plasma zinc concentration, reductions in urinary zinc excretion, and impaired cell-mediated immune responses (9). However, in the present study the low-zinc diet was provided for a shorter period of time (5 wk compared with 7 wk), so the study subjects may not have been as zinc depleted as those in the earlier study. We measured the current subjects' serum zinc concentration and total urinary zinc excretion at intervals during the study to assess their zinc status in relation to the dietary manipulations. Although we found a transient decrease in mean serum zinc concentration after the first week of the low zinc dietary period, this value returned to the baseline concentration by the end of this dietary period. Thus, it appears that, although the subjects may have had some degree of zinc depletion, this was probably mild. There were no significant changes in urinary zinc excretion by dietary period, possibly because it tends to respond more slowly than does serum zinc concentration to changes in dietary zinc intake (3).

With regard to the issue of statistical power, the available sample size permitted detection of a difference of 0.10 in FZA in relation to the longer-term dietary effect. Thus, even if differences in absorption might occur in relation to longer-term dietary zinc intake, the magnitude of such changes would be relatively small compared with the observed effect of the current zinc intake. Thus, altered efficiency of intestinal absorption after longer-term exposure to modifications in zinc intake does not appear to be a major regulatory mechanism for maintaining zinc homeostasis. Indeed, other studies of zinc kinetics have found that conservation of endogenous fecal losses seems to be the primary means of regulating whole-body zinc balance during longer periods of time (5, 6, 17).

In summary, current dietary zinc intakes inversely influence the efficiency of zinc absorption and directly affect the total amount of zinc that is absorbed. The magnitude of these effects is considerably greater than any putative effect of longer-term zinc intake and consequent changes in zinc status. Although it is conceivable that a more prolonged period of very low zinc intakes (<4 mg/d) might exert a greater effect on zinc absorption, such extremely low zinc intakes are probably uncommon in free-living adults.


   ACKNOWLEDGMENTS
 
We thank Dustin Burnett, Cathy Hsu, and Ana Perez-Exposito for their invaluable assistance recruiting and implementing the clinical study, and all the volunteers that participated.

The author's responsibilities were as follows—CSC: managed all aspects of the clinical study, including subject recruitment, planning and implementation of the clinical study, data interpretation, and initial draft of the manuscript; DD: was involved in diet design, meal provision, and monitoring diet compliance; RW: conducted the phytate analyses; TQN and RR: conducted mineral and zinc stable isotope analyses; JMP and JS: conducted statistical analyses; KHB and JCK: contributed to the study concept, research design, data interpretation, and manuscript revision. All authors critically reviewed the manuscript. None of the authors had a personal or financial conflict of interest.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

  1. Sandstrom B. Dose dependence of zinc and manganese absorption in man. Proc Nutr Soc 1992;51:211–8.[Medline]
  2. López de Romaña D, Salazar M, Hambidge KM, et al. Longitudinal measurements of zinc absorption in Peruvian children consuming wheat products fortified with iron only or iron and 1 of 2 amounts of zinc. Am J Clin Nutr 2005;81:637–47.[Abstract/Free Full Text]
  3. Wada L, Turnlund JR, King JC. Zinc utilization in young men fed adequate and low zinc intakes. J Nutr 1985;115:1345–54.[Abstract/Free Full Text]
  4. Taylor CM, Bacon JR, Aggett PJ, Bremner I. Homeostatic regulation of zinc absorption and endogenous losses in zinc-deprived men. Am J Clin Nutr 1991;53:755–63.[Abstract/Free Full Text]
  5. Lee D-Y, Prasad AS, Hydrick-Adair C, Brewer G, Johnson PE. Homeostasis of zinc in marginal human zinc deficiency: role of absorption and endogenous excretion of zinc. J Lab Clin Med 1993;122:549–56.[Medline]
  6. King JC, Shames DM, Lowe NM, et al. Effect of acute zinc depletion in men on zinc homeostasis and plasma zinc kinetics. Am J Cin Nutr 2001;74:116–24.
  7. Hotz C, Peerson JM, Brown KH. Suggested lower cutoffs of serum zinc concentrations for assessing zinc status: reanalysis of the second National Health and Nutrition Examination Survey data (1976–1980). Am J Clin Nutr 2003;78:756–64.[Abstract/Free Full Text]
  8. Institute of Medicine. Dietary reference intakes: vitamin a, vitamin k, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc. Washington, DC: National Academy Press, 2002.
  9. Ruz M, Cavan KR, Bettger WJ, Thompson L, Berry M, Gibson RS. Development of a dietary model for the study of mild zinc deficiency in humans and evaluation of some biochemical and functional indices of zinc status. Am J Clin Nutr 1991;53:1295–303.[Abstract/Free Full Text]
  10. Harris J, Benedict F. A biometric study of basal metabolism in man. Washington, DC: Carnegie Institute of Washington, 1919.
  11. Fung EB, Ritchie LD, Woodhouse LR, Roehl R, King JC. Zinc absorption in women during pregnancy and lactation: a longitudinal study. Am J Clin Nutr 1997;66:80–8.[Abstract/Free Full Text]
  12. Lowe NM, Shames DM, Woodhouse LR, et al. A compartmental model of zinc metabolism in healthy women using oral and intravenous stable isotope tracers. Am J Clin Nutr 1997;65:1810–9.[Abstract/Free Full Text]
  13. Friel JK, Naake VL Jr, Miller LV, Fennessey PV, Hambidge KM. The analysis of stable isotopes in urine to determine the fractional absorption of zinc. Am J Clin Nutr 1992;55:473–7.[Abstract/Free Full Text]
  14. Shames DM, Woodhouse LR, Lowe NM, King JC. Accuracy of simple techniques for estimating fractional zinc absorption in humans. J Nutr 2001;131:1854–61.[Abstract/Free Full Text]
  15. Brown KH, Chung CS, King JC, Peerson JM, Shames DM. A modified double isotope tracer ratio (DITR) technique to estimate fractional Zn absorption (FZA) using the slope of urinary tracer-tracee ratios (TTRs) FASEB J 2005;19:A973.
  16. Lowe NM, Woodhouse LR, Sutherland B, et al. Kinetic parameters and plasma zinc concentration correlate well with net loss and gain of zinc from men. J Nutr 2004;134:2178–81.[Abstract/Free Full Text]
  17. Miller LV, Hambidge KM, Naake VL, Hong Z, Westcott JL, Fennessey PV. Size of the zinc pools that exchange rapidly with plasma zinc in humans: alternative techniques for measuring and relation to dietary zinc intake. J Nutr 1994;124:268–76.[Abstract/Free Full Text]
Received for publication October 11, 2007. Accepted for publication December 5, 2007.




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Y. Song, C. S Chung, R. S Bruno, M. G Traber, K. H Brown, J. C King, and E. Ho
Dietary zinc restriction and repletion affects DNA integrity in healthy men
Am. J. Clinical Nutrition, August 1, 2009; 90(2): 321 - 328.
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K. M. Hambidge, L. V. Miller, J. E. Westcott, and N. F. Krebs
Dietary Reference Intakes for Zinc May Require Adjustment for Phytate Intake Based upon Model Predictions
J. Nutr., December 1, 2008; 138(12): 2363 - 2366.
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