Serum Leptin in Children With Obesity: Relationship to Gender and Development

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Serum

Leptin

in Children

With

Obesity:

Relationship

to Gender

PEDIATRICS Vol. 98 No. 2 August 1996 201

and

Development

Sandra G. Hassink, MD*; David V. Sheslow, PhD; Elizabeth de Lancey, BS; Irma Opentanova,

PhDII;

Robert V. Considine, PhDII; and Jose F. Caro, MDII

ABSTRACT. Background. The identification of the ob

gene and its adipocyte-specific protein leptin has pro-vided the first physiologic links to the regulatory system controlling body weight. In adults, elevations of serum leptin concentrations were closely correlated with the percentage of body fat. This study investigated whether

leptin concentrations were elevated in obese children

and the relationship between leptin concentrations and gender, pubertal stage, and race.

Methods. Seventy-seven children (44 girls and 33 boys), mean age, 11.3 years, with a body mass indices (BMIs) greater than 95% for age, race, and gender (mean BMI, 34.4) constituted the obese group. Thirty children (20 girls and 10 boys), mean age, 13.3 years, with BMIs less than 85% for age, race, and sex formed the control group. Radioimmuno-assay for serum leptin was performed on a blood sample

collected from each child after an overnight fast

Results. The mean serum concentration of leptin in the obese group was 38.6 (SD, 21) ng/mL compared with

7.8 (SD, 6.5) nglmL in the control group. Serum leptin

concentrations were highly correlated with BMI (r .88).

Analysis of covariance revealed a main effect for Tanner stage and gender.

Conclusions. As in adults, obese children have high concentrations of serum leptin, which were highly cor-related with arm fat and BMI. Increased adipose tissue in children is associated directly with serum leptin

concentration. Leptin concentrations were found to

vary with Tanner stage independent of adiposity.

Compared with boys, girls had increased leptin

con-centrations independent of adiposity. It was hypothe-sized that children manifest a relative “leptin resis-tance” to support increased growth and development of reproductive capacity. Pediatrics 1996;98:201-203; childhood obesity, growth, development.

ABBREVIATIONS. BMI, body mass index; ANCOVA, analysis of

covariance.

The identification of the

ob

gen& and its adipocyte-specific protein leptin has provided the first physio-logic links to the regulatory system controlling body

weight. It is thought that leptin is integral in the

feedback loop from adipose stores to the satiety centers

From the *pj.tnent f Pediatrics, tDivision of Psychology, and §Depart-ment of Clinical Science, Alfred I duPont institute, Wilmington, Delaware; and IlDivision of Endocrinology and Metabolism, Jefferson Medical College of Thomas Jefferson University, Philadelphia.

Received for publication Mar 22, 1996; accepted Apr 22, 1996.

Reprint requests to (S.C.H.) Alfred I duPont Institute, Department of Pedi-attics, 1600 Rockland Rd, Wilmington, DE 19899.

PEDIATRICS (ISSN 0031 4005). Copyright C 1996 by the American Acad-emy of Pediatrics.

in the hypothalamus,2 causing a decrease in appetite and increase in energy expenditure. An increase in the expression of the ob gene has been found in the adipo-cytes of obese adults.25 In normal and obese adults, the amount of

ob

messenger RNA in adipocytes correlated

with body weight.24 Recently, Considine et al2

re-ported that leptin has been detected in the serum of

obese and normal-weight adults, with obese adults

having significantly higher serum leptin concentrations than do normal-weight adults. Elevations of serum

lep-tin concentrations were most dosely correlated with

the percentage of body fat.

Unlike adults, children are in a dynamic relationship with their energy needs for growth and development. This raises the possibility that leptin may ftmction

dif-ferently in the developing person than in adults. The

purpose of the present study was to investigate whether leptin can be detected in the serum of obese children and, if so, whether serum leptin levels directly

correlate with body fat as they do in adults and to

investigate whether leptin concentrations vary with

gender, race, and growth and development.

METHODS Children

Table I presents demographic and anthropometric data for the

obese and control groups. The obese group was composed of 77

children (44 girls and 33 boys) with a mean age 11.25 (SD, 4) years

presenting to a hospital-based, outpatient weight-management

program. All obese children had body mass indices (BMIs; weight

in kilograms divided by the square of height in meters) greater

than the 95th percentile for age, race, and gender.6 The mean BMI

for the obese group was 34.4 (SD, 7.6). Thirty normal-weight

children (20 girls and 10 boys) with a mean age of 13.2 (SD, 3.5)

years constituted the control group. All children in the control

group had BMIs less than the 85th percentile for age, race, and

gender. The mean BMI for the control group was 18.9 (SD, 3.1).

Children in the control group were seen as outpatients referred for blood testing from other departments of the hospital. Both parents and children gave informed consent. The study was approved by

the Institutional Review Board of the Alfred I duPont Institute.

Procedures

A blood sample was collected from each child after an

over-night fast. The serum was frozen at 80#{176}Cuntil analysis. Radioim-munoassay for serum leptin was performed as previously dis-cussed by Considine et al.2 Height was measured by stadiometer to the nearest centimeter; weight was measured to the nearest 0.1

kg on a balance beam scale; and BMI was calculated. Systolic and

diastolic blood pressures were obtained in the right arm with the

child seated, by mercury manometer, and triceps skin fold was

measured at the midarm distance to the nearest millimeter using

Lange calipers. Measurement of waist circumference was at the

umbilicus, and hip circumference was measured at the widest point to the nearest 0.5 cm in all children. Arm fat was calculated

at Viet Nam:AAP Sponsored on September 1, 2020

www.aappublications.org/news

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* Values are mean (SD). tP < .02.

:1:P < .003.

§

p < .001. IIP< .04

from the measured midarm drcumference and triceps skin fold

according to the formulas provided by Must and colleagues.’ Tanner stage was determined by examination in the obese children and by questionnaire in the control group.

Statistical Analysis

Demographic and anthropometric measurements between the obeseand controlgroupswere comparedby meansoft tests. Because of extreme values in the distribution of serum leptin concentrations and estimates of percentages of body fat, the relations between the continuous variables were evaluated by Spearman rank correlations. A log transformation of serum leptin levels was performed to xr-malize the distribution for subsequent analyses. All analyses were

performed ung the general factorial arulysis of covariai

(AN-COVA)model, controlling for the effects ofboth BMI and upper-arm fat estimates of body fat used because of the previously reported2 high correlation between serum leptin concentration and body fat estimates. Posthoc analyses were performed to determine differences between Tanner stages, No adjustments were made for multiple

t-Y-%mT1iQnnQ PnQfl1n( w1wpt. mn1ra1#{149} ,nwm pHmafp nfflRfl

10 20 30 40

Body Mw (w)

Figure. The relation between body mass index and serum leptin concentrations in 77 obese and 30 control subjects.

202 SERUM LEPTIN IN CHILDREN WITH OBESITY

TABLE 1. Demographic

Obese and Control Groups

and Anthropometric Variables in

Variable Obese (n=77) Control (n=30) Age5 lly3mo (4y) l3y3mo (3y6mo)t Gender

M 33 10

F 44 20

Race

White 52 29

Nonwhite 25 1

Body mass index, weight/heighP Arm fat, mm2*

34.4 (7.6)

4702.7 (3826.7)

18.9 (3.1)

1463.7 (710.9)

Waisthip ratios 0.86 (0.10) 0.82(0.08)11

Systolic blood pressure, 113 (13) 107 (12)11

mmHg

Diastolic blood pressure, 69 (11) 66 (10)

mmHg

-.r---.-

----r---or greater for all comparisons. Data are presented as the mean arid

SD. All analyses were two tailed and coixiucted with the SPSS

software (version 6.0 for Wmdows; SPSS lix, chicago, IL).

RESULTS

Table 2 presents laboratory findings for the obese

and control groups. The mean ages were 11.4 (SD, 4)

years for the obese group and 13.3 (SD, 3.5) years for the control group (P < .02). There were, however, no

differences in Tanner stage. Consequently, age was

.. ..

% . ..

.. .‘:

40 . :#{149} .

. ..% ..

.- . ..:. . #{149}

1 .

C

TABLE 2. Labora tory Variables in 0 bese and Control Groups

Variable Obese (n = 77),

Mean (SD)

Control (n = 30),

Mean (SD)

Leptin, ng/ml 38.6 (21) 7.8 (6.5)*

Insulin, uU/ml 24.0 (16.5) 16.3 (14.1)t

* P < .001.

tP < .05.

not used as a covariate in analyses. As expected, the

obese group had a higher BMI (P < .001), upper-arm fat area (P < .001), and waist-to-Hp ratio

(P

< .04) than the control group.

The mean serum leptin concentration in the obese

group was 38.6 (SD, 21) ng/mL, compared with 7.8

(SD, 6.5) ng/mL in the control group (P < .001). All

children had detectable leptin concentrations. The

lowest serum leptin concentration detected in a child

presenting with obesity was 4.9 ng/mL, and the

highest was 84.6 ng/mL

For the combined group (obese and control),

se-rum leptin concentrations were highly correlated with BMI

(r

= .88; P < .001) and upper-arm fat area

(r

= .88;

P < .001). The Figure demonstrates the relationship

between BMI and serum leptin concentrations for all

children. Leptin concentrations were moderately corre-lated with fasting insulin levels

(r

= .51; P < .001).

To investigate the relationship between leptin and

gender a 2 (group)

x

2 (gender) ANCOVA was

performed. Main effects for group (F = 21.80;

P

<

.001) and gender (F = 31.65; P < .001) were found

with the obese group, and girls demonstrated higher

leptin levels. No interactions were found.

A 2 (gender)

x

3 (Tanner stage) ANCOVA was

performed to investigate the role of leptin independent

of estimates of body fat. Tanner stages 1 and 2 and 3

and 4 were collapsed to provide a greater number in

each cell. This analysis revealed a main effect for Tan-ner stage (F = 4.99; P < .009). Table 3 prents log

leptin concentrations across Tanner stages. Posthoc

analysis suggested a significant difference between

Tanner stages 1 and 2 and Tanner stage 5 (P < .01). A

main effect for gender (F = 2336; P < .001) was also

found, with girls having higher serum leptin concert-trations than boys. No interactions were found.

To investigate the effect of racial differences on

leptin concentrations in children, independent of es-ti.mate of body fat, a 2 (race) X 2 (gender) ANCOVA

was performed. African-American and Hispanic

children were collapsed into one group because of an

insufficient number of Hispanic children per cell,

preventing a more complete analysis. As expected, a

main effect for gender was found (F = 10.58; P <

.002). However, no main effect or interactions with

race reached significance. DISCUSSION

Leptin is found in high concentrations in obese

chil-dren. Leptin concentrations were highly correlated

with arm fat area and BMI, the indirect measures of

adiposity used in this study. Serum leptin concentra-tions in normal-weight children were comparable with

those found in normal-weight adults Leptin

concert-trations in obese children were comparable with those

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ARTICLES 203 TABLE

Controllin

3. Log Serum Leptin

g For Adiposity

Tanner Stage

I and 2

3and4 5

Levels Across Tanner Stages

Log Leptin

303* 2.99 2.65

*p < .#{216}.

found in obese adults2 (Table 4). There were no

differ-ences in leptin concentrations because of race. As in

adults, obese children had increases in serum leptin

concentrations directly proportional to their levels of adiposity. This finding has led to a hypothesis of a resistance to the action of leptin at the level of the

hypothalamus7 causing increased appetite and

de-creased energy expenditure despite adequate leptin

production by adipocytes.

Leptin concentrations were found to vary with

Tanner stage in both normal-weight and obese

chil-dren independent of adiposity. Table 3 presents

mean log leptin concentrations for Tanner stages I and

2, 3 and 4, and 5. In an animal analogue, the assodation

between leptin and pubertal development has been

described. Chehab et al found that in ob/ob mice, which produce no leptin because of a defective

ob

gene,

pu-berty does not advance until exogenous leptin is

ad-ministered. Although the mechanism has yet to be

described, it is likely that leptin plays a role in human growth and development.

To account for the finding of decreased leptin con-centrations with advanced Tanner stage, it is hypothe-sized that prepubertal children manifest a central in-sensitivity to leptin or relative “leptin resistance” in the service of their dynamic energy needs. As adolescents

approach the end of puberty, energy needs and

adi-pose stores stabilize, and leptin sensitivity returns.

High concentrations of leptin in obese adults,

de-spite maintenance of increased appetite and

de-creased energy expenditure, led to the hypothesis of

central leptin resistance.7’ Higher leptin

concentra-tions in prepubertal compared with postpubertal

children may suggest that leptin resistance is part of normal growth and development.

Leptin concentrations were increased in girls in

both the obese and control groups. This effect was

independent of Tanner stage when controlling for

adiposity. As growth ends in adulthood, gender

dif-ferences in leptin concentrations disappear.2 In the

developing girl, adipose tissue accumulation acceler-ates from 16% at 6 years to 23% at 18 years.1#{176}This study covaried for body fat; therefore, gender differ-ences cannot be explained on the basis of adiposity. Because leptin concentrations are increased

indepen-dent of adiposity, it is reasonable to speculate that

central leptin resistance in developing girls may be

necessary for the accumulation of the adipose tissue

stores necessary for reproduction.11’3

Children’s relative resistance to leptin may be a

TABLE 4. Serum Leptin Concentrations in Obese and Control

Children and Adults

Group Children, ng/mL,

Mean (SD)

Adults2, ng/mL,

Mean (SD)

Obese 38.6 (21) 31.3 (21.1)

Controls 7.8 (6.5) 7.5 (9.3)

part of the normal growth process, allowing

in-creased energy accumulation for growth by

damp-ening the afferent satiety signal in the feedback loop

in the hypothalamic appetite and satiety centers.7

Changing levels of resistance may signal the end of

growth in adolescence. Obesity, then, may be a per-turbation of the normal process of relative leptin resistance necessary for growth and development.

These findings should be interpreted cautiously, par-ticularly in light of the small number of normal-weight children studied. Longitudinal studies will be neces-sary to support the hypothesis that leptin resistance is part of the normal process of growth and development in childhood.

ACKNOWLEDGMENTS

This work was supported by grants from the Nemours

Foun-dation, Alfred I duPont Institute (Drs Hassink, Sheslow, and de

Lancey), National Institutes ofHealth (Drs Opentanova and Caro),

and American Diabetes Association (Dr Considine).

We thank Dr Joseph Glutting for his statistical support and Dr Alan Spitzer for his guidance.

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1996;98;201

Pediatrics

Considine and Jose F. Caro

Sandra G. Hassink, David V. Sheslow, Elizabeth de Lancey, Irina Opentanova, Robert V.