9 1987 by The Humana Press Inc. All rights of any nature, whatsoever, reserved. 0163-4984/87/1400-0053502.20

Zinc, Copper, Selenium, and Glutathione Peroxidase in Blood of 1 1-Yr-Old Dunedin, New Zealand Children J O A N M. M C K E N Z I E - P A R N E L L * AND CHRISTINE D. T H O M S O N

Department of Human Nutrition, University o f Otago, Dunedin, NZ Received October 24, 1986; Accepted November 2, 1986

ABSTRACT Blood was obtained from 564 ll-yr-old children who had participated since birth in a multidisciplinary health and development study. Serum zinc concentration did not differ between the boys and the girls (mean _+ SD: 91 + 17 ~zg/100 mL, n = 453). Five-6% of serum zinc values were low; although there was a weak correlation with height, none of the boys with low values were below the 10th percentile for height for this group. Serum copper concentration (112 _+ 24 ~g/100 mL, n = 454) was unrelated to sex, height, weight, body mass index, socioeconomic status (SES), or iron status. Blood selenium concentration (49 + 10 ng/mL, n = 564) was lower than previously reported for Dunedin children; it was higher in children in the lower SES categories. The data represent normal values for healthy, ll-yrold NZ children. Index Entries: Zinc, in children; copper, in children; selenium, in children; glutathione peroxidase, in children.

INTRODUCTION The status of NZ adults with respect to zinc, copper, a n d selenium has been investigated for s o m e years by the p r e s e n t investigators. Alt h o u g h the zinc status of NZ adults is j u d g e d to be normal (1), a n d their c o p p e r status s o m e w h a t low (2), their selenium status is notably low by *Author to whom all correspondence and reprint requests should be addressed.

Biological Trace ElementResearch

53

Vol. 14, 1987

54

McKenzie-Parnell and Thomson

international values (3,4). The trace element profile of this country's soils explains the values for these consumers at the end of the food chain. Very little is known of the trace element status of pre-adolescent children in NZ. All of these three essential trace elements will produce growth deficits in deficient animals. More particularly, human zinc deficiency was first reported in the Middle East in pre-adolescents with symptoms including growth retardation and delayed sexual maturation (5). Although serum is the most commonly used, it is not a good measure of zinc or copper status in children unless they are demonstrably deficient (6). Children with protein-energy malnutrition, for example, with many of the clinical features of zinc deficiency, commonly have low plasma zinc concentrations (7). Low serum copper concentrations have also been observed, as have low selenium values in such children. In NZ subjects, whole blood selenium concentration and glutathione peroxidase (GSH-Px) activity are reliable indicators of a low dietary selenium intake (3,8). In 1972 a prospective study of all children born over a 12-mo period at Dunedin's only public maternity hospital recruited more than 1000 children. The health and development of those children have been followed until the present time (9). As the children in the cohort attained their l l t h birthdays, the opportunity was taken to obtain blood samples for the analysis of serum zinc and copper and whole blood selenium and GSH-Px levels. There has been only one previous report of serum zinc concentrations in prepubertal children in NZ. For the 30 (anesthetized) children in the 5-12-yr age group, serum zinc concentration was comparable with overseas values for children (10).

METHODS

Study Sample The sample for this study comprised 61% (selenium), 49% (zinc and copper), and 18% (GSH-Px), respectively, of the 925 children assessed as part of the 11-yr follow-up of the Dunedin Multidisciplinary Health and Development Study. The study sample is known to be over-representative of the higher socioeconomic levels and under-representative of Maori and other Polynesian children; full details of the study and the sample are contained elsewhere (9,11). Some children were assessed at centers other than Dunedin, but all of the children participating in this traceelement study were among the 802 children assessed at the research unit in Dunedin within 2 mo of their 11th birthday; 90% lived in the Dunedin metropolitan area. Of the 379 girls seen at the research unit, 6 had begun to menstruate at the time of their assessment.

Biological TraceElementResearch

VoL 14, 1987

Zinc, Copper, and Selenium in NZ Children

55

Parameters Approximately 30 mL venous blood was collected from each child who freely agreed to participate; this blood was used for a variety of purposes. The blood was obtained between 8:45 and 9:45 AM from the nonfasting subjects between February 1983 and March 1984. Care was taken at all stages to avoid trace-element contamination of the samples that were stored either frozen after separation of the serum (for zinc and copper analysis) or chilled (for selenium and GSH-Px analyses). Sera were analyzed in duplicate for zinc and copper after dilution with 6% butanol (1). Replicate analyses of a synthetic "control" serum (Cation Cal Calibration Reference, DADE, Hospital Supply Corporation, Miami, FL) produced zinc and copper concentrations within 5% of the stated concentrations; reproducibility of the assay was +2.3% for zinc and +3.1% for copper. Selenium in whole blood was analyzed by the automated fluorimetric method of Watkinson (12,13). Sensitivity and sample reproducibility of the method was 0.1 ppb and + 2.5% within the range 0-100 ppb. The GSH-Px was assayed by a modification (14) of the coupled method of Paglia and Valentine (15), using t-butyl hydroperoxide (0.3 mM) as substrate and 3 mM glutathione at 25~ pH 7.3. Anthropometric and other data were obtained on the same day of blood sampling, using trained personnel. The sample's background characteristics were assessed by use of Johnston's (16) revision of the Elley and Irving (17) Index of Socioeconomic Status (SES). This NZ scale is based on median income and education for occupations; in the present study the fathers' occupations when the children were 11 yr of age were used. Examples of occupations for particular SES levels are given in Table 1. The data were analyzed statistically using both parametric and nonparametric methods. TABLE 1 Socioeconomic Status (SES) Levels and Examples of Occupations ~ SES Level

Examples of occupations Accountant, doctor, university lecturer Author, estate agent, journalist, social worker Bank officer, chef, photographer, tool maker Baker, electrician, grocer, signwriter Cook, lorry driver, storeman, welder Cleaner, farm hand, miner, van driver

"From ref. (16).

Biological Trace Element Research

VoL 14, 1987

h4cKenzie-Parnell and Thomson

56

RESULTS Log transformation of the data did not improve the small degree of skewness in the data for serum zinc, serum copper, blood selenium, or GSH-Px activity; the data presented here is untransformed. The values for zinc, copper, selenium, or GSH-Px did not differ significantly between the boys and girls (Table 2) nor was there a significant seasonal variation in any of the measures. One value for whole blood selenium (138 ng/mL) was excluded from the analysis of the data because it was 43 ng/mL above the next highest value for selenium for the group; subsequently, it was found that that boy n o w lived overseas and had been on holiday in Dunedin, at which time his blood sample was obtained. Five-percent of values for serum zinc were low using the criterion (18) of more than 2 SD below the mean (i.e., 57 ~g Zn/100 mL). Elevenpercent of serum zinc values were low using the cutoff of 70 I~g Zn/100 mL; six-percent were below 65 Izg Zn/100 mL. The lowest zinc value of 40 t~g Zn/100 mL was observed in a boy whose serum copper was 128 ~g/100 mL and w h o s e blood selenium was 45 ng/mL. Two-percent of values for serum copper were more than 2 SD below the m e a n (i.e., 64 p,g Cu/100 mL). The lowest copper concentration of 42 ~g/100 mL was observed in a boy whose serum zinc was 89 I~g/100 mL and whose blood selenium was 44 ng/mL. Four-percent of values for serum copper were above 160 tzg Cu/100 mL (i.e., were more than 2 SD above the mean). The zinc and copper concentrations were normal in the boy with the lowest selenium value of 25 ng/mL and in the boy with the highest selenium value of 95 ng/mL. TABLE 2 Serum Zinc, Serum Copper, Blood Selenium, and GSH-Px Levels in Dunedin Children Subjects

Serum zinc, ~zg/100 mL

Serum copper, /zg/100 mL

Blood selenium, ng/mL

GSH-Px, U/g Hb

90 + 17~ (207)~ 92 +- 17 (246) 91 + 17 (453) 92' 40-160' ~

112 _+ 24 (207) 111 +- 23 (247) 112 + 24 (454) 110 42-190

48 + 9 (259) 50 + 10 (305) 49 ___ 10 (564) 49 25--95

18.4 _+ 5.1 (81) 18.1 + 4.9 (87) 18.2 + 5.0 (168) 178 8.5-38.7

Girls Boys All subjects

"Mean +_ SD. "Number of subjects. 'Median. '~Range.

Biological Trace KlementResearch

VoL 14, I987

Zinc, Copper, and Selenium in NZ Children

57

P e a r s o n correlation coefficients for the data, as well as for height, w e i g h t , b o d y m a s s index (BMI), a n d SES are p r e s e n t e d in Table 3. S e r u m zinc c o n c e n t r a t i o n w a s n e g a t i v e l y correlated with s e r u m c o p p e r concentration, w h e r e a s w h o l e b l o o d s e l e n i u m c o n c e n t r a t i o n a n d G S H - P x activity w e r e s t r o n g l y positively correlated. S e r u m zinc c o n c e n t r a t i o n w a s positively correlated with height, b u t n o t with w e i g h t or BMI; w h o l e b l o o d s e l e n i u m c o n c e n t r a t i o n w a s correlated with SES. F u r t h e r investigation of t h e relationship b e t w e e n s e r u m zinc a n d h e i g h t s h o w e d that the correlation w a s n o t significant for the girls (r = 0.00136, p = 0.428), w h e r e a s it w a s for the b o y s (r = 0.1510, p = 0.013). H o w e v e r , d e s p i t e the significance of this correlation, o n l y 2% of the variance in height w a s e x p l a i n e d b y this relationship with s e r u m zinc for the b o y s . O n e - w a y analysis of variance again r e v e a l e d a statistically significant (p

Zinc, copper, selenium, and glutathione peroxidase in blood of 11-yr-old dunedin, New Zealand children.

Blood was obtained from 564 11-yr-old children who had participated since birth in a multidisciplinary health and development study. Serum zinc concen...
569KB Sizes 0 Downloads 0 Views