ORIGINAL PAPER

Jpn J Reprod Endocrinol ⓒ2003 by
Japan Society of Reproductive Endocrinology

Serum Leptin Levels in Women throughout Life;
Relationship to Body Mass Index and Serum Estradiol Levels
Masayo YAMADA, Toshiya MATSUZAKI, Takeshi IWASA, Fumi SHIMIZU, Naoko TANAKA, Rie OGATA,
Machiko KIYOKAWA, Toshiyuki YASUI, Minoru IRAHARA and Toshihiro AONO
Department of Obstetrics and Gynecology, The University of Tokushima, School of Medicine, Tokushima 770-8503, Japan

Abstract. In order to investigate serum leptin levels and the influence of estradiol on these levels throughout the female lifespan, leptin and estradiol levels in sera of females that ranged from adolescent to old age (pre-menarche,
post-menarche, menstrual cycle, pregnancy, post-partus, pre-menopause, post-menopause) were examined using radioimmunoassays. The serum leptin level was positively correlated with the BMI and the Rohrer index (p < 0.01) inthe various age groups from schoolgirls to menopausal women. Serum leptin levels during the normal menstrual cycle negligibly changed, and no differences were detected between pre-menopause and post-menopause women.
Moderate changes of estradiol levels in sera during menarche, normal menstrual cycle and menopause had no influence on the serum leptin levels. As expected, serum leptin levels in pregnant women were higher than that in nonpregnant women.
The present results are summarized as follows: 1) Serum leptin levels correlated with BMI at all ages. 2) Moderateincreases in serum estradiol levels had no effect on serum leptin levels. 3) Serum leptin levels are significantly increased during pregnancy, possibly due to an excessive increase of leptin production from maternal adipose tissue
that is stimulated by high concentrations of serum estradiol and leptin production from the placenta.

Key words: Leptin, Estradiol, Body mass index

Introduction

responsible for the modulation of serum leptin levels inwomen of reproductive age [8]. However, the cause of

Leptin is produced in adipose tissues and secreted intohigher leptinemia in women remains unclear.

the peripheral blood [1, 2]. Leptin acts on the hypothala-

Administration of leptin or factors, which regulate obmus, which contains leptin receptors [3], and it plays anmRNA expressions such as glucocorticoids and insulin,important role in the maintenance of energy homeostasis

correct reproductive functions of female ob/ob mice, in-and the regulation of metabolic activities.

ducing ovulation, pregnancy and parturition [9, 10, 11]. In

Previous studies have shown that the serum concentra-

earlier studies, we reported that women who received

tion of leptin in human sera is well correlated with bodyovarian hyperstimulation through IVF/ICSI showedmass index (BMI) and the percentage of body fat. It is

higher serum leptin levels when serum estradiol (E2) lev-

also known that the concentrations of leptin are signifi-

els were greatly elevated [12], and that E2 increased thecantly higher in women than in men of the same BMI [4,expression of ob mRNA in adipose tissue of ovariecto-

5, 6, 7]. In addition, it has been demonstrated that serum

mized rats [13] and in cultured rat adipose cells [11].

leptin levels are higher in pregnant women than in puer-

These findings indicate that E2 levels could influence theperal women and that factors other than fat mass could beserum leptin levels. Since serum E2 concentrations
change dramatically throughout the female lifespan, se-

Accepted: August 19, 2003
Correspondence: Toshiya MATSUZAKI, Department of
Obstetrics and Gynecology, The University of Tokushima,
School of Medicine, 3-18-15, Kuramoto-cho, Tokushima
770-8503, Japan
TEL: +81-886-33-7177
FAX: +81-886-31-2630
E-mail: mat@clin.med.tokushima-u.ac.jp

rum leptin levels might change in parallel to E2 levels.
In this study, we measured the serum leptin levels inwomen of various ages and conditions, and analyzed therelationship between the leptin and E2 levels.

Japanese Journal of Reproductive Endocrinology (2003) 8 : 55-60

55

Masayo YAMADA et al.

Materials and methods
１）Subjects and blood sampling
The subjects of this study were 216 females, aged 6 to

± S.D., respectively). (4) Peri-menopausal women, whose
age ranged from 40 to 67 years old (n = 95, 49.8 ± 0.5
years old), and who were further divided into pre-menopause (n = 29) and post-menopause (n = 66) groups.

67 years. None of the subjects were taking any medication

The weight and height of the subjects were measured

nor had any evidence of metabolic diseases aside fromin light clothing without shoes. Body mass index (BMI,

simple obesity. All subjects provided written informed

calculated as weight in kilograms divided by the square ofconsent for the procedures of this study. The subject cate-height in meters, kg/m2) and the Rohrer index in the casegories were as follows: (1) Peri-menarche girls whose ageof schoolgirls (calculated as weight in grams divided byranged from 6 to 15 years old (n = 22, 10.8 ± 0.5 years old,the cube of height in centimeters multiplied by 100, g/cm3

mean ± SEM), and who were further divided into pre-X 100) were used as indexes of overall adiposity. Serummenarche (n = 11), and post-menarche (n = 11) groups.

samples were frozen at -40℃ until assayed.

(2) Reproductive-age females who had a normal menstrual cycle as evidenced by basal body temperature (n = 22,

２）Measurement of leptin and estradiol in serum

30.0 ± 1.0 years old). Blood samples were collected three

A specific radioimmunoassay for serum leptin using hu-

times from each subject at the early follicular, pre-ovula-

man recombinant leptin as a tracer was performed as pre-tory and mid-luteal phases in this group. (3) Pregnant fe-

viously described by Iida et al [14]. The minimum value ofmales (n = 61) and age-matched puerperal females (n =detection was 0.5 ng/mL. The intra-assay standard coeffi-14), who were divided into four groups (1st trimester: 8.9

cient of variation (CV) was 7.8 %, and the inter-assay CV± 0.4 weeks, 2nd trimester: 22.7 ± 1.5 weeks, 3rd trimes-

was 5.6 %. Samples were assayed in duplicate.

ter: 35.4 ± 0.5 weeks, and one month after delivery, mean

Serum concentrations of E2 were measured using a

Table 1. Body mass index and serum leptin and estradiol concentrations

56

Japanese Journal of Reproductive Endocrinology Vol. 8 2003

Leptin, BMI & Estradiol in Women throughout Life

coated-tube immunoassay kit (Diagnostic Products Corp.,
Los Angeles, CA) according to the manufacturer's protocols. The minimum value of detection was 8 pg/mL. The
intra-assay CV was 8.1%, and the inter-assay CV was 5.0%.
Serum samples from pregnant women were diluted twoand fourfold with the buffer included in the kit. Samples
were assayed in duplicate.
BMI (kg/m2)

３）Statistical analysis
All data were expressed as the mean ± SE. Differencesamong the groups were tested by one-way ANOVA. WhenFig. 1. Relationship between serum leptin and BMI (r = 0.71, p <0.01, y = -10.5 + 1.5 * X) of 22 peri-menarche girls
Serum leptin levels were significantly correlated with BMI.

P < 0.05 was detected by a one-way ANOVA, a Scheffe's test
was also performed. Pearson product-moment correla-

E2 in the post-menarche group were significantly higher

tions were calculated to test the association among thethan those in the pre-menarche group (Table 1). Serum

variables. Partial correlation tested for the associations

leptin levels were significantly correlated with BMI (Fig. 1

between the two variables and was performed indepen-

and Table 2), and were not significantly correlated withdently of the covariate. Repeated measurements were ana-age.

lyzed by a Student's paired t-test.

２）The changes of serum leptin levels during normal menstrual cycle

Results
１）The levels of leptin in sera of peri-menarche girls

The BMI of reproductive-age females ranged from 16.6
to 26.5 (20.9 ± 0.5) kg/m2. Although the levels of E2 were

The BMI of peri-menarche females ranged from 13.7 tosignificantly changed during the menstrual cycle, no sig-

36.2 (19.3 ± 2.2: mean ± SE) kg/m2, and their Rohrer in-nificant change in leptin levels was observed (Table 1).

3

dex ranged from 89.6 to 244.5 (137.3 ± 7.6) g/cm X 100.

Serum leptin levels were significantly correlated with

Leptin levels were not significantly different between the

BMI, but were not significantly correlated with age or es-

pre-menarche and post-menarche groups, but the levels of

tradiol (Table 2).

Table 2. Correlations between serum leptin concentrations and various parameters

ORIGINAL PAPER

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Masayo YAMADA et al.

BMI(kg/m2)

Fig. 2. The change of serum leptin and E2 levels in pregnant, puerperal and non-pregnant women (follicular phase)□, leptin concentration; ●, estradiol concentration. Error bars
depict SD. *p < 0.05 vs. 1st, 2nd & 3rd trimester, #p < 0.01
vs. 3rd trimester, **p < 0.01 vs. 2nd & 3rd trimester. The estradiol levels were higher in the pregnant women than in the
non-pregnant and puerperal women. Ratio of leptin to BMI
was higher in pregnant women than in the non-pregnant andpuerperal women.

Fig. 3. The relationship between serum leptin levels and BMI in
peri-menopausal women (r = 0.68, p < 0.01, y = -40.9 + 3.0* X)
Serum leptin levels were significantly correlated with BMI.

ranged from 16.6 to 33.3 (23.7 ± 0.4) kg/m2. Serum leptin
levels were significantly correlated with BMI and were notcorrelated with age or estradiol levels (Fig. 3, Table 2).
Serum leptin levels were not significantly different be-３）The levels of leptin in pregnant women
BMIs, levels of leptin and estradiol in pregnant and agematched non-pregnant women (follicular phase) are

tween the pre-menopausal and post-menopausal women,
while E2 levels were significantly higher in the pre-menopausal women (p < 0.01) than in the post-menopausal
women (Table 1).

shown in Table 1. The mean BMI prior to pregnancy inthe pregnant group was 21.2 ± 3.5 and this was not significantly different from that of the normal menstrual group.

Discussion

As shown in Table 1, the mean BMI in the 3rd trimester

Serum leptin primarily originates from the fat tissue andgroup was higher than that seen in the 1st trimester andits level is an important signal for the brain with regard toin non-pregnant women. Serum estradiol levels were sig-

regulating appetite and energy homeostasis. Present find-nificantly higher in the pregnant women than in the follic-ings demonstrated that serum leptin levels are correlated

ular phase women and puerperal women, and gradually

positively with BMI and the Rohrer index at all ages, rang-

increased during pregnancy. Serum leptin levels were also

ing from peri-menarche to peri-menopausal females.

significantly higher in the pregnant women than in the fol-

Leptin levels were not different between pre-menarche

licular phase and puerperal women. Leptin levels in preg-and post-menarche, pre-menopause and post-menopause,nant women were correlated with BMI, but not correlatedor during the normal menstrual cycle (follicular, pre-ovu-

with age or estradiol (Table 2).

latory, and luteal phases). Our data indicates that adipose

To eliminate the influence of increased BMI in preg-

cells always produce regular amounts of leptin irrespec-

nancy, the relationship between the estradiol and leptin/

tive of age or menstrual status. It is reasonable to assume

BMI ratio was examined. As shown in Fig. 2, the leptin/that the serum leptin level accurately reflects the amount

BMI ratios of the 3 pregnancy groups were significantlyof fat storage in the body.

higher than those for the non-pregnant or puerperal women, respectively.
４）Leptin levels in peri-menopausal women

Elevation of the serum leptin level, which precedes puberty, is thought to play an important role in the onset ofpuberty. Our data clearly shows that elevation of the serum leptin level during puberty does not reflect the capac-

The relationship between BMI and serum leptin level in

ity of leptin production by each adipose cell, but rather in-

the peri-menopausal women is shown in Fig. 3. Their BMI

dicates fat mass stored in the body. Constant synthesis of58

Japanese Journal of Reproductive Endocrinology Vol. 8 2003

Leptin, BMI & Estradiol in Women throughout Life

leptin from each adipose cell enables the brain to know

large amount of E2, the E2 level in the mother's serum in-the exact amount of energy that is stored in the body.

creases during pregnancy, but decreases rapidly after de-

Our study found that serum leptin levels were highly

livery. This change parallels the changes of serum leptin

correlated with body composition (BMI or percent bodyduring and after pregnancy. It seems likely that a largefat). Other studies have reported that serum leptin levels

quantity of E2 has an effect on the leptin production in theare higher in women than in men, in the fetus [15, 16], in

adipose tissues of the mother. Therefore, the source ofchildren [17, 18], and in adults [5, 6, 7]. Interestingly, it ishigh leptin levels in pregnant women may not only bereported that E2 stimulates the production of ob mRNA infrom production in the placenta but also from the mater-

both cultured rat adipose cells [11] and adipose tissues ofnal adipose cells that are stimulated by a high concentra-

ovariectomized rats [13].

tion of E2 originating from the placenta.

It might be conceivable that E2 has a stimulatory effectIn summary, the measurement of serum leptin levels

on the production of leptin in women. However, the E2 ef-

obtained throughout women's lifetimes disclosed the fol-fect on leptin is controversial. Our data suggests that se-lowing findings: (1) Serum leptin levels are correlated

rum leptin levels are not correlated with the E2 levels

with BMI at all ages. (2) A moderate increase in the se-seen throughout women's lifetimes. Havel et al. has also

rum estradiol level has no effect on serum leptin levels.

reported that absolute and adiposity-corrected plasma(3) Serum leptin levels significantly increase during preg-

leptin levels were independent of both age and reproduc-

nancy, possibly due to an excessive increase of leptin pro-tive status in women [7]. In addition, Havel et al. [7] andduction from the maternal adipose tissue that is stimu-

Kohrt et al. [19] reported that leptin levels were not affect-

lated by a high concentration of serum estradiol and leptin

ed by hormone replacement therapy (HRT). However,production from the placenta.

Rosenbaum et al. reported that leptin levels were significantly higher in pre-menopausal women than in postmenopausal women [20]. We previously reported that serum leptin levels became elevated when serum E2 levels
rose in ovarian hyperstimulated women receiving IVF-ET[12]. These data suggest that E2 might induce leptin production under conditions of high concentrations of E2.
The serum leptin levels and leptin/BMI ratios during
pregnancy were significantly higher than those in nonpregnant women, and increased from the 1st to the 3rdtrimester. The leptin levels were lower in puerperal women than in pregnant women, and were the same as thoseseen in non-pregnant women. BMI does not necessarilyreflect body fat mass in pregnant women, and the remarkable increase of the serum leptin level during pregnancy
is not explicable by an increase of fat mass alone. It has
been suggested that the incremental increase of leptin
during pregnancy is caused by production in the placenta[21].
Ob mRNA is expressed in the placenta, and the placental leptin may contribute to an increase in serum leptin
levels in the mother [15]. However, placental leptin cannot fully explain the elevation of leptin levels during pregnancy because placental weight does not correlate withmaternal leptin levels [22]. As the placenta produces a

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