ABSTRACT

Background: Early on childbearing may limit skeletal consolidation and increase calcium demands in adolescents.

Objective: The purpose of this written report was to characterize calcium absorption in pregnant and lactating adolescents.

Blueprint: Partial calcium absorption was evaluated in 23 adolescents (mean ± SD age: 16.5 ± i.4 y) during the third trimester of pregnancy (34.7 ± 1.0 wk gestation) and again in 15 of these adolescents 31 ± 8 d later on commitment. Eight adolescents were breastfeeding their infants during the follow-up report. Fractional calcium assimilation was adamant past using oral (46Ca or 44Ca) and intravenous (42Ca) stable calcium isotopes. Full-trunk and lumbar spine os mineral density were measured in adolescents during the postpartum period by using dual-energy Ten-ray absorptiometry.

Results: Fractional calcium assimilation was significantly greater during pregnancy than at iii–4 wk postpartum [0.526 ± 0.152 (n = 23) compared with 0.297 ± 0.108 (north = xv); P < 0.0001]. Lumbar spine z scores measured 19–44 d after delivery (northward = fifteen) were significantly associated with calcium intake during pregnancy (y = −iii.53 + 0.10710; R 2 = 0.355, P < 0.02) and were inversely related to fractional calcium assimilation during pregnancy (y = 3.489 − half dozen.66x; R 2 = 0.52, P = 0.002). A total of 33% (five/15) of adolescents had lumbar spine z scores that met the definition of osteopenia (due north = 3) or osteoporosis (due north = 2) in the early on postpartum period.

Conclusions: Calcium absorption in adolescents was significantly higher during the tertiary trimester of pregnancy than in the early postpartum menstruum, and higher calcium intakes during pregnancy appeared to exist protective against loss of trabecular bone at the lumbar spine.

INTRODUCTION

Boyish pregnancy is currently a pregnant public health problem. Each year, ≈ten% of all 15–19-y-old women go meaning (1). Of these, ≈52% (or more than half a million teens) comport children, and > 175 000 of these new mothers are aged ≤ 17 y (1). Despite recent decreases in nascency rates (2), the 1999 nascency rate for US teenagers anile 15–19 y was 49.half dozen per 1000 women (3). This rate was markedly college in African American adolescents, averaging 81.1 per 1000 women anile 15–19 y compared with 34.1 per one thousand white women of a similar age (3).

Childbearing can take a substantial impact on nutrient demands, peculiarly for nutrients such as calcium that are required for bone evolution. During the superlative catamenia of adolescent skeletal accession, females deposit an boilerplate of seven.1 mmol (284 mg) Ca/d into bone (4). In meaning adolescents, these maternal calcium requirements are coupled with the need to provide ≈1.25 mmol (50 mg) Ca/d to the fetus at 20 wk of gestation and 8.25 mmol (330 mg) Ca/d by 35 wk of gestation (v). These increased demands approximately double calcium demands in pregnant adolescents and may adversely bear upon attainment of peak bone mass.

To conform the increased calcium demands of pregnancy, fractional calcium absorption in adult women increases significantly during the 3rd trimester of pregnancy compared with prepregnancy or postpartum values (6–ix). The additional calcium demands of pregnancy may touch os mass over the grade of pregnancy. Longitudinal bone density studies in adult women typically written report bone mineral density losses of iii.two–4.6% at trabecular sites over the 9-mo course of pregnancy compared with prepregnancy values (10, 11). Although losses have been reported at trabecular sites, increases in os mineral density at cortical bone sites have also been reported during pregnancy (12). Breastfeeding also causes temporal losses of trabecular bone mineral at the spine and hip (≈three–five%) over the first 3–6 mo of lactation (13). Despite these changes, however, most studies institute no relation between parity and duration of breastfeeding and subsequent risk of osteoporosis (13).

Young maternal historic period may influence bone loss during pregnancy and lactation. Earlier historic period at start pregnancy has been associated with both lower cortical bone density in midlife or later (fourteen, 15) and persistent reductions in adult hip bone density (xvi). Significantly greater os loss at the heel has also been reported in still-growing adolescents compared with adult women (17). Moreover, increased bone loss has been reported in lactating adolescents compared with adult women (18, 19).

Few data currently exist on the ability of adolescents to alter intestinal calcium absorption during pregnancy and lactation. The purpose of our study was to examine the efficiency of fractional calcium absorption and changes in urinary calcium and hormone concentrations between pregnancy and the early on postpartum period in adolescent females.

SUBJECTS AND METHODS

Discipline recruitment

Pregnant adolescents (≤ eighteen y of age) were recruited from the Baltimore area betwixt 1996 and 2002. All adolescents were healthy, had uncomplicated singleton pregnancies, and were having their outset child. None had medical problems or were taking whatsoever medications known to influence calcium metabolism. Study volunteers were nonsmokers and did not have a self-reported history of drug or booze abuse. Informed written consent was obtained from the report participants, and the study protocol was approved past the Johns Hopkins University Institutional Review Board.

Calcium absorption studies

Pregnant adolescents were admitted to the Pediatric Clinical Research Unit (PCRU) at Johns Hopkins Hospital when they were between 32 and 36 wk of gestation. Adolescents were admitted to the PCRU the evening before the calcium infusion, and baseline weight and height measurements were obtained. The following forenoon, a fasting baseline blood sample was obtained for analysis of calcium-related hormones. With breakfast, each daughter received either 46Ca (0.0075 μmol/kg) or 44Ca (0.005 mmol/kg) orally in milk; 42Ca (0.025 mmol/kg) was administered intravenously immediately after breakfast. Girls remained in the PCRU in a private room for the 120 h after dosing. A 24-h urine collection was obtained postdosing, and 3 spot urine collections were obtained daily for the remainder of the report. Adolescents self-selected their foods during the vi-d written report, and each food item was weighed before and later on intake during the inpatient study to decide actual dietary intakes. Average calcium intake for each dietary menses was adamant as the mean of the v 24-h weighed-nutrient records completed during the inpatient study. The Minnesota NUTRIENT DATABASE SYSTEM (version ii.91; University of Minnesota, Minneapolis) was used to calculate nutrient intakes. All adolescents were asked to return for a second calcium study when their infant was between iii and 7 wk of age.

Bone mineral content

Full-trunk and lumbar spine bone mineral content (BMC) and body composition were measured in each boyish during the postpartum menstruum past using dual-free energy 10-ray absorptiometry (Hologic QDR 2000 W, software version 8.26a:3; Hologic Inc, Waltham, MA). Lumbar spine z scores were generated past using the Hologic database. Osteopenia at this site was defined as a z score > i SD below predicted values and osteoporosis every bit a z score > ii SDs below predicted values.

The total-trunk BMC of each adolescent was compared with a total-trunk BMC reference database, equally previously reported (20), with adjustment for height, age, sex, and ethnicity. A ratio was then derived betwixt actual and predicted total-body BMC to decide the consequence of pregnancy on predicted total-body BMC in the early postpartum period. Values > 1 SD beneath predicted values were defined as indicating osteopenia, and values > two SDs beneath age-matched predictive values were defined as indicating osteoporosis.

Isotope analysis and calculations

Calcium isotope ratios were measured by using thermal ionization mass spectrometry (Finnigan Triton TI, Bremen, Germany) (21, 22). The ratio of each administered tracer to 48Ca or 43Ca was measured, and the caste to which this ratio was increased over the natural abundance ratio was calculated.

Fractional calcium absorption was determined as the relative recovery of the oral and the intravenous tracer in the 24-h urine drove postdosing. Total calcium concentrations in urine were measured by using atomic absorption spectrophotometry (Perkin Elmer model 3300; Perkin Elmer, Norwalk, CT). The equations used in these determinations were reported previously (23). Truthful calcium absorption was calculated as the production of partial calcium assimilation and the average 5-d calcium intake. Endogenous fecal calcium losses were estimated to be 1.5 mg · kg−i · d−one on the basis of data suggesting that these losses were not affected past pregnancy (9). Calcium residual was determined by subtracting the sum of urinary and estimated endogenous fecal calcium losses from true calcium absorption.

Hormone analysis

Serum concentrations of 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D were measured past using radioimmunoassays (Diasorin, Inc, Stillwater, MN). Samples from the same individual were run in the same assay to reduce intraassay variation, which was within 10% for both assays. Serum estradiol was measured with an enzyme immunoabsorbant assay (DSL Laboratories, Webster, TX).

Serum North-telopeptide concentrations were measured in baseline serum samples, and urinary Due north-telopeptide was measured in the 24-h urine collection obtained for each calcium intake menstruum by using enzyme-linked immunoabsorbant assays (Ostex International, Inc, Seattle). Urinary creatinine concentrations were measured in 24-h urine samples past using a colorimetric analysis (Quidel Corporation, Santa Clara, CA).

Statistical analyses

Statistical analyses were carried out by using STATVIEW data analysis software (version five.0.1; SAS Institute Inc, Berkeley, CA). Paired t tests were used to determine pregnant differences between pregnancy and postpartum periods for each of the measured variables in adolescents who completed both studies. Pupil'southward t test was used to decide significant differences between lactating and nonlactating adolescents. Analysis of variance was used to address group contrasts betwixt the pregnancy and the postpartum written report and to examine potential differences in measured variables between the lactating and nonlactating adolescents. Elementary regression assay was used to examine potential relations betwixt calcium absorption and other measured variables. Results were considered pregnant if P values were < 0.05.

RESULTS

The characteristics of the study population are presented in Tabular array 1. The age of the adolescents averaged 16.5 ± ane.4 y at the time of entry into the study (range: 13.v–xviii.three y). Of the 23 adolescents, 20 were African American and 3 were white. A total of fifteen of the 23 adolescents returned for the 2d report nineteen–44 d subsequently giving birth. Of these, 53% were breastfeeding their infants. All breastfeeding adolescents were African American. There were no significant differences in baseline characteristics (historic period, elevation, weight, body mass alphabetize, or week of gestation) between the adolescents who returned for the postpartum study and those who did non.

TABLE i

Characteristics of the adolescents during pregnancy and in the postpartum period

Pregnancy (n = 23) Postpartum, nonlactating (n = 7) Postpartum, lactating (n = 8)
Age (y) 16.5 ± 1.4 1 xv.half dozen ± i.half-dozen 17.ii ± 1.1 2
Weight (kg) 75.7 ± eighteen.4 70.ane ± 17.4 68.four ± sixteen.8
Height (cm) 162.vi ± 5.1 161.3 ± four.2 162.iv ± 6.0
BMI (kg/m2) 28.7 ± 7.3 xxx.0 ± 6.two 27.7 ± 7.0
Time of gestation (wk) 34.seven ± i.0 — —
Racial group (n)
    African American xx 4 8
    White three 3 0
Time postpartum (d) — 28.6 ± seven.nine 32.1 ± seven.7
Pregnancy (north = 23) Postpartum, nonlactating (n = 7) Postpartum, lactating (n = eight)
Historic period (y) 16.v ± ane.4 1 15.6 ± i.6 17.2 ± 1.1 2
Weight (kg) 75.seven ± eighteen.four 70.i ± 17.4 68.4 ± sixteen.8
Tiptop (cm) 162.6 ± 5.1 161.three ± four.two 162.4 ± 6.0
BMI (kg/chiliad2) 28.seven ± 7.3 xxx.0 ± vi.ii 27.vii ± 7.0
Time of gestation (wk) 34.7 ± one.0 — —
Racial group (n)
    African American xx 4 8
    White 3 three 0
Time postpartum (d) — 28.half-dozen ± 7.ix 32.1 ± seven.7

ane

x̄ ± SD.

2

Significantly different from the nonlactating postpartum group, P < 0.05 (Pupil's t examination).

TABLE i

Characteristics of the adolescents during pregnancy and in the postpartum catamenia

Pregnancy (north = 23) Postpartum, nonlactating (northward = 7) Postpartum, lactating (n = 8)
Age (y) 16.5 ± i.iv 1 fifteen.6 ± 1.half-dozen 17.2 ± i.ane two
Weight (kg) 75.vii ± 18.4 70.1 ± 17.iv 68.4 ± xvi.8
Height (cm) 162.6 ± 5.1 161.three ± 4.2 162.4 ± six.0
BMI (kg/grandtwo) 28.vii ± seven.3 xxx.0 ± 6.2 27.7 ± 7.0
Time of gestation (wk) 34.seven ± 1.0 — —
Racial grouping (due north)
    African American 20 4 viii
    White 3 3 0
Time postpartum (d) — 28.6 ± seven.9 32.1 ± 7.7
Pregnancy (due north = 23) Postpartum, nonlactating (n = 7) Postpartum, lactating (n = 8)
Age (y) 16.v ± 1.four 1 fifteen.6 ± one.6 17.2 ± i.one 2
Weight (kg) 75.7 ± eighteen.four 70.1 ± 17.four 68.four ± 16.8
Height (cm) 162.6 ± 5.i 161.iii ± 4.2 162.4 ± half-dozen.0
BMI (kg/m2) 28.7 ± 7.three 30.0 ± half dozen.two 27.7 ± vii.0
Time of gestation (wk) 34.seven ± 1.0 — —
Racial grouping (n)
    African American 20 4 8
    White 3 3 0
Fourth dimension postpartum (d) — 28.6 ± seven.9 32.i ± vii.vii

i

x̄ ± SD.

ii

Significantly unlike from the nonlactating postpartum grouping, P < 0.05 (Educatee'due south t test).

Variables related to calcium residuum for the pregnancy and postpartum studies are presented in Table ii. Calcium intakes were based on self-selected diets and included the contribution of calcium in prenatal supplements (5 mmol). Despite daily reminders from the dietary staff of the PCRU, only 39% (9/23) and 40% (half-dozen/15) of the adolescents took prenatal supplements during the pregnancy and postpartum studies, respectively, and if consumed, supplements were ofttimes not consumed daily.

TABLE 2

Calcium absorption and estimated residue in adolescents during pregnancy and in the postpartum period 1

Pregnancy (n = 23) Postpartum, nonlactating (due north = vii) Postpartum, lactating (n = 8) 2
Calcium intake (mmol/d) 29.65 ± nine.40 24.59 ± 11.07 33.86 ± 9.83
Partial absorption (%) 0.526 ± 0.152a 0.329 ± 0.114b 0.268 ± 0.101b
Calcium captivated (mmol/d) 15.30 ± five.54a viii.09 ± v.eighteenb nine.03 ± 2.81b
Urinary calcium (mmol/d) 6.44 ± 2.13a 1.25 ± 0.72b i.82 ± 0.89b
Estimated residual (mmol/d) 3 6.03 ± 5.fifteen iv.21 ± 5.27 4.65 ± 2.82
Pregnancy (due north = 23) Postpartum, nonlactating (n = vii) Postpartum, lactating (n = eight) 2
Calcium intake (mmol/d) 29.65 ± 9.40 24.59 ± 11.07 33.86 ± 9.83
Fractional assimilation (%) 0.526 ± 0.152a 0.329 ± 0.114b 0.268 ± 0.101b
Calcium absorbed (mmol/d) 15.30 ± 5.54a 8.09 ± 5.xviiib 9.03 ± 2.81b
Urinary calcium (mmol/d) 6.44 ± 2.thirteena ane.25 ± 0.72b 1.82 ± 0.89b
Estimated balance (mmol/d) 3 6.03 ± 5.15 iv.21 ± 5.27 four.65 ± ii.82

1

x̄ ± SD. Values within a row with unlike superscript messages are significantly different, P < 0.05 (ANOVA with Bonferroni-Dunn multiple-comparison test).

2

n = 7 for calcium intake, calcium absorbed, and estimated rest because calcium intake data were not available for ane adolescent.

three

Assumes endogenous fecal losses of 1.5 mg·kg−1·d−1; derived as calcium captivated − urinary calcium − endogenous fecal losses. No pregnant differences in estimated residuum were axiomatic past using ANOVA with Bonferroni-Dunn multiple-comparison tests, just differences approached significance betwixt the pregnancy and postpartum studies when using paired t tests (P = 0.09).

Tabular array 2

Calcium assimilation and estimated balance in adolescents during pregnancy and in the postpartum flow 1

Pregnancy (n = 23) Postpartum, nonlactating (n = 7) Postpartum, lactating (northward = eight) 2
Calcium intake (mmol/d) 29.65 ± ix.40 24.59 ± eleven.07 33.86 ± 9.83
Fractional absorption (%) 0.526 ± 0.152a 0.329 ± 0.114b 0.268 ± 0.101b
Calcium absorbed (mmol/d) fifteen.30 ± 5.54a 8.09 ± 5.18b ix.03 ± 2.81b
Urinary calcium (mmol/d) 6.44 ± 2.xiiia i.25 ± 0.72b 1.82 ± 0.89b
Estimated residue (mmol/d) 3 half dozen.03 ± 5.15 iv.21 ± 5.27 four.65 ± 2.82
Pregnancy (n = 23) Postpartum, nonlactating (north = 7) Postpartum, lactating (north = viii) ii
Calcium intake (mmol/d) 29.65 ± ix.twoscore 24.59 ± xi.07 33.86 ± 9.83
Partial absorption (%) 0.526 ± 0.152a 0.329 ± 0.114b 0.268 ± 0.101b
Calcium absorbed (mmol/d) xv.30 ± 5.54a 8.09 ± 5.18b 9.03 ± 2.81b
Urinary calcium (mmol/d) 6.44 ± 2.xiiia ane.25 ± 0.72b i.82 ± 0.89b
Estimated balance (mmol/d) 3 6.03 ± 5.xv four.21 ± five.27 4.65 ± 2.82

i

x̄ ± SD. Values within a row with different superscript messages are significantly dissimilar, P < 0.05 (ANOVA with Bonferroni-Dunn multiple-comparing test).

2

n = 7 for calcium intake, calcium absorbed, and estimated balance because calcium intake data were non bachelor for 1 adolescent.

iii

Assumes endogenous fecal losses of 1.5 mg·kg−1·d−1; derived as calcium absorbed − urinary calcium − endogenous fecal losses. No significant differences in estimated rest were axiomatic by using ANOVA with Bonferroni-Dunn multiple-comparing tests, merely differences approached significance between the pregnancy and postpartum studies when using paired t tests (P = 0.09).

Within the group of 23 meaning adolescents, fractional calcium assimilation tended to exist college in adolescents with college urinary Due north-telopeptide concentrations (R 2 = 0.157, P = 0.09, n = xix). Fractional calcium absorption was unrelated to other biochemical indicators. No pregnant relation was evident between partial calcium absorption and calcium intake during either pregnancy or the postpartum menstruation across the range of intakes consumed by these adolescents (13–45 mmol/d). However, a relation of fractional absorption to intake may take been difficult to discover in this group, because seventy% of adolescents consumed > 25 mmol/d and but four adolescents consumed < twenty mmol/d (range: 12.v–18 mmol/d). Similarly, fractional calcium absorption during pregnancy or in the early postpartum menstruum was not significantly affected past historic period across the age range of xiii–xviii y. Higher calcium intakes were related to a significantly higher estimated calcium residue during pregnancy (P < 0.005, R two = 0.332, n = 23) and lactation (P < 0.05, R 2 = 0.406, n = fourteen); calcium intake was not significantly related to urinary calcium excretion during pregnancy or lactation in this historic period group.

Significant alterations in hormonal concentrations and markers of os turnover were observed during pregnancy compared with the postpartum period, irrespective of lactation status ( Table three). During pregnancy, serum 1,25-dihydroxyvitamin D (163.i ± 94.5 pmol/L; P < 0.0001, paired t examination, n = xiv) and estradiol (xiv.ane ± 5.9 nmol/L; P < 0.0001, paired t examination, n = 13) concentrations were significantly higher and serum North-telopeptide (−v.229 ± four.965 nmol os collagen equivalents; P < 0.002, paired t test, n = 14) concentrations were significantly lower in the adolescents who went on to consummate both studies, irrespective of lactation status. No significant differences in hormone concentrations or in other study variables were axiomatic between the nonlactating and lactating adolescents. Despite the small number of white adolescents, 25-hydroxyvitamin D concentrations were significantly lower in the African American adolescents than in the white adolescents during both pregnancy [44.5 ± sixteen.2 (n = 20) compared with ninety.2 ± xiii.0 (n = three) nmol/L; P < 0.001] and the postpartum [38.4 ± 19.6 (n = 13) compared with 92.iv ± 1.0 (northward = 2) nmol/L; P < 0.005] studies.

Table 3

Calcium-related hormones and bone turnover markers in adolescents during pregnancy and in the postpartum menstruation ane

Pregnancy Postpartum, nonlactating Postpartum, lactating
25-Hydroxyvitamin D (nmol/L) fifty.5 ± iv.6 [23] 52.vii ± 10.nine [7] 39.iii ± 8.5 [8]
1,25-Dihydroxyvitamin D (pmol/Fifty) 232.iii ± 20.1 [23]a 93.2 ± vii.vii [vii]b 81.4 ± 7.ix [vii]b
Serum N-telopeptide (nmol BCE) 23.6 ± i.ii [23] 26.9 ± 7.4 [7] 26.iv ± 2.0 [seven]
Urinary N-telopeptide (nmol BCE/mmol creatinine) 813.vi ± 147.two [19] 1196.7 ± 226.ii [vi] 1163.5 ± 303.ane [eight]
Estradiol (nmol/L) 13.7 ± 1.2 [22]a 0.453 ± 0.151 [7]b 0.618 ± 0.136 [7]b
Pregnancy Postpartum, nonlactating Postpartum, lactating
25-Hydroxyvitamin D (nmol/50) 50.5 ± 4.six [23] 52.seven ± x.nine [7] 39.3 ± 8.5 [8]
i,25-Dihydroxyvitamin D (pmol/L) 232.three ± xx.one [23]a 93.2 ± vii.7 [seven]b 81.4 ± seven.ix [vii]b
Serum North-telopeptide (nmol BCE) 23.6 ± 1.2 [23] 26.ix ± vii.4 [7] 26.4 ± 2.0 [vii]
Urinary N-telopeptide (nmol BCE/mmol creatinine) 813.6 ± 147.2 [19] 1196.7 ± 226.2 [6] 1163.5 ± 303.1 [8]
Estradiol (nmol/L) xiii.vii ± 1.ii [22]a 0.453 ± 0.151 [7]b 0.618 ± 0.136 [7]b

1

x̄ ± SEM; n in brackets. BCE, bone collagen equivalent. Values within a row with unlike superscript messages are significantly different, P < 0.001 (ANOVA with Bonferroni-Dunn multiple comparing exam).

TABLE iii

Calcium-related hormones and bone turnover markers in adolescents during pregnancy and in the postpartum period 1

Pregnancy Postpartum, nonlactating Postpartum, lactating
25-Hydroxyvitamin D (nmol/50) 50.5 ± 4.6 [23] 52.vii ± ten.9 [7] 39.iii ± 8.v [8]
1,25-Dihydroxyvitamin D (pmol/L) 232.3 ± 20.1 [23]a 93.two ± seven.7 [7]b 81.4 ± 7.ix [vii]b
Serum Northward-telopeptide (nmol BCE) 23.6 ± 1.2 [23] 26.9 ± vii.4 [vii] 26.4 ± 2.0 [vii]
Urinary N-telopeptide (nmol BCE/mmol creatinine) 813.six ± 147.2 [xix] 1196.7 ± 226.two [6] 1163.5 ± 303.1 [eight]
Estradiol (nmol/L) thirteen.vii ± 1.2 [22]a 0.453 ± 0.151 [seven]b 0.618 ± 0.136 [7]b
Pregnancy Postpartum, nonlactating Postpartum, lactating
25-Hydroxyvitamin D (nmol/Fifty) 50.5 ± 4.6 [23] 52.7 ± 10.9 [7] 39.3 ± 8.five [eight]
1,25-Dihydroxyvitamin D (pmol/50) 232.3 ± 20.1 [23]a 93.two ± vii.7 [7]b 81.iv ± seven.nine [seven]b
Serum Due north-telopeptide (nmol BCE) 23.6 ± one.2 [23] 26.9 ± 7.4 [7] 26.4 ± 2.0 [7]
Urinary Due north-telopeptide (nmol BCE/mmol creatinine) 813.half-dozen ± 147.2 [19] 1196.7 ± 226.2 [6] 1163.v ± 303.ane [8]
Estradiol (nmol/Fifty) 13.7 ± 1.2 [22]a 0.453 ± 0.151 [7]b 0.618 ± 0.136 [7]b

1

x̄ ± SEM; due north in brackets. BCE, os collagen equivalent. Values within a row with dissimilar superscript messages are significantly different, P < 0.001 (ANOVA with Bonferroni-Dunn multiple comparison test).

Among all subjects who completed both studies, total-body BMC fell below 98% of the predicted value in five of 15 adolescents (33%); in these v adolescents (3 lactating and 2 nonlactating), total-torso BMC was eight ± 3.half dozen% lower than expected given the historic period, meridian, and ethnicity of the adolescent. Site-specific decreases in BMC were likewise axiomatic. Lumbar spine z scores averaged −0.075 and ranged betwixt −two.33 and 2.39. With the use of lumbar spine z scores, iii girls in the report would have been considered osteopenic (z score < −one), and 2 girls would have been considered osteoporotic (z score < −2), ie, 33% of the report population had bear witness of deficits in trabecular skeletal mass in the early on postpartum period. Although there were no significant differences in physical characteristics or calcium intake between the lactating and nonlactating adolescents, lumbar spine z scores were on average −0.9 SD lower (NS) in lactating adolescents ( Table 4).

Tabular array 4

Bone mineral content in adolescents during the postpartum period 1

Nonlactating (northward = vii) Lactating (n = viii)
TBBMC (g) 2119.5 ± 280.ix (1771.2–2673.1) 2 2270.3 ± 226.0 (1937.3–2612.6)
Predicted TBBMC (g) 2020.4 ± 191.7 (1816.ane–2360.half-dozen) 2276.eight ± 231.0 iii (1939.7–2583.vi)
BMC:BMCp i.102 ± 0.136 (0.898–1.289) 1.001 ± 0.090 (0.882–1.127)
LS z score 0.399 ± 1.716 (−2.33–2.39) −0.489 ± ane.315 (−two.130–1.38)
Osteopenic: LS z score < −1 (n) 2 1
Osteoporotic: LS z score < −two (n) ane 1
Nonlactating (north = 7) Lactating (northward = viii)
TBBMC (m) 2119.5 ± 280.9 (1771.2–2673.1) 2 2270.3 ± 226.0 (1937.iii–2612.6)
Predicted TBBMC (yard) 2020.iv ± 191.7 (1816.1–2360.six) 2276.8 ± 231.0 3 (1939.7–2583.6)
BMC:BMCp one.102 ± 0.136 (0.898–i.289) 1.001 ± 0.090 (0.882–1.127)
LS z score 0.399 ± i.716 (−2.33–ii.39) −0.489 ± 1.315 (−two.130–1.38)
Osteopenic: LS z score < −1 (n) 2 ane
Osteoporotic: LS z score < −2 (n) 1 1

i

TBBMC, total-torso bone mineral content; BMC:BMCp, ratio of measured to predicted TBBMC (22); LS, lumbar spine.

ii

x̄ ± SD; range in parentheses.

3

Significantly different from the nonlactating group, P < 0.05 (Student's t test).

Tabular array 4

Bone mineral content in adolescents during the postpartum period 1

Nonlactating (north = 7) Lactating (north = 8)
TBBMC (one thousand) 2119.5 ± 280.9 (1771.two–2673.ane) 2 2270.iii ± 226.0 (1937.3–2612.half dozen)
Predicted TBBMC (g) 2020.iv ± 191.seven (1816.one–2360.vi) 2276.8 ± 231.0 3 (1939.7–2583.vi)
BMC:BMCp 1.102 ± 0.136 (0.898–1.289) one.001 ± 0.090 (0.882–1.127)
LS z score 0.399 ± 1.716 (−ii.33–two.39) −0.489 ± 1.315 (−2.130–1.38)
Osteopenic: LS z score < −ane (due north) 2 one
Osteoporotic: LS z score < −2 (n) i 1
Nonlactating (due north = 7) Lactating (n = 8)
TBBMC (g) 2119.five ± 280.nine (1771.ii–2673.i) two 2270.3 ± 226.0 (1937.3–2612.6)
Predicted TBBMC (g) 2020.iv ± 191.7 (1816.1–2360.6) 2276.8 ± 231.0 3 (1939.vii–2583.vi)
BMC:BMCp ane.102 ± 0.136 (0.898–one.289) 1.001 ± 0.090 (0.882–i.127)
LS z score 0.399 ± ane.716 (−2.33–2.39) −0.489 ± 1.315 (−2.130–1.38)
Osteopenic: LS z score < −1 (due north) two 1
Osteoporotic: LS z score < −2 (n) 1 1

i

TBBMC, total-body bone mineral content; BMC:BMCp, ratio of measured to predicted TBBMC (22); LS, lumbar spine.

2

x̄ ± SD; range in parentheses.

iii

Significantly different from the nonlactating group, P < 0.05 (Student's t test).

Of the variables measured, lumbar spine z scores were inversely related to fractional calcium absorption during pregnancy (y = 3.489 − 6.6610; R 2 = 0.520, P = 0.002, n = fifteen; Effigy 1). Lumbar spine z scores in the early postpartum period were too significantly positively influenced past calcium intake assessed during the third trimester of pregnancy (y = −3.53 + 0.107x; R 2 = 0.355, P < 0.02) just were non related to calcium intakes during the early postpartum menses. In that location were no significant relations between the length of time that had elapsed betwixt the pregnancy and postpartum studies and either lumbar spine z scores or the pct of predicted total-body BMC.

Figure 1.

Calcium absorption was measured with stable calcium isotopes during the third trimester of pregnancy (35 ± 1 wk gestation) in 2 nonlactating white adolescents (▴) and 13 African American adolescents [n = 5 nonlactating (•) and n = 8 lactating (○)]. Lumbar spine z scores were measured on average 30 d postpartum by use of dual-energy X-ray absorptiometry. A significant inverse relation was evident between fractional calcium absorption and lumbar spine z scores: y = 3.489 − 6.66x (R2 = 0.520, P = 0.002, n = 15). In this group, 33% of the adolescents were either osteopenic (lumbar spine z score > −1; n = 3) or osteoporotic (lumbar spine z score > −2; n = 2) in the early postpartum period.

Calcium assimilation was measured with stable calcium isotopes during the 3rd trimester of pregnancy (35 ± 1 wk gestation) in 2 nonlactating white adolescents (▴) and 13 African American adolescents [n = 5 nonlactating (•) and n = viii lactating (○)]. Lumbar spine z scores were measured on average 30 d postpartum by utilise of dual-free energy X-ray absorptiometry. A meaning inverse relation was evident between fractional calcium absorption and lumbar spine z scores: y = 3.489 − 6.66x (R ii = 0.520, P = 0.002, north = 15). In this grouping, 33% of the adolescents were either osteopenic (lumbar spine z score > −1; n = 3) or osteoporotic (lumbar spine z score > −ii; n = 2) in the early postpartum period.

Figure 1.

Calcium absorption was measured with stable calcium isotopes during the third trimester of pregnancy (35 ± 1 wk gestation) in 2 nonlactating white adolescents (▴) and 13 African American adolescents [n = 5 nonlactating (•) and n = 8 lactating (○)]. Lumbar spine z scores were measured on average 30 d postpartum by use of dual-energy X-ray absorptiometry. A significant inverse relation was evident between fractional calcium absorption and lumbar spine z scores: y = 3.489 − 6.66x (R2 = 0.520, P = 0.002, n = 15). In this group, 33% of the adolescents were either osteopenic (lumbar spine z score > −1; n = 3) or osteoporotic (lumbar spine z score > −2; n = 2) in the early postpartum period.

Calcium absorption was measured with stable calcium isotopes during the third trimester of pregnancy (35 ± 1 wk gestation) in ii nonlactating white adolescents (▴) and 13 African American adolescents [n = 5 nonlactating (•) and northward = 8 lactating (○)]. Lumbar spine z scores were measured on average 30 d postpartum by use of dual-energy X-ray absorptiometry. A meaning inverse relation was axiomatic between fractional calcium absorption and lumbar spine z scores: y = 3.489 − 6.66x (R 2 = 0.520, P = 0.002, north = 15). In this grouping, 33% of the adolescents were either osteopenic (lumbar spine z score > −i; n = three) or osteoporotic (lumbar spine z score > −ii; n = two) in the early postpartum menses.

Word

The extent of the increase in calcium absorption in response to pregnancy has not been previously examined in adolescents. In our study population of pregnant adolescents, pct calcium absorption averaged 53% during pregnancy and was nearly 60% higher than values measured 3–4 wk after delivery. Even though adolescents in this age range are unlikely to accept accomplished acme bone mass, calcium assimilation in this age group did not markedly differ from information reported for pregnant adults (6, 7, 9). Previous studies in pregnant women in their tertiary trimester (consuming calcium intakes ranging from 931 to 1350 mg/d) found similar calcium assimilation values, averaging 56.0 ± 2.0% [northward = four (6)], 53.8 ± 11.3% [n = 14 (7)], and 47.iv ± 13.3% [n = 8 (ix)]. Moreover, within our population, calcium absorption was not significantly affected past age across the range of 13–eighteen y, nor did boilerplate absorption in adolescents anile ≤ 15 y (n = vii) differ significantly from that observed in adolescents aged ≥ xvi y. We are enlightened of no other studies focusing on calcium absorption in pregnant adolescents. Ane early written report reported calcium absorption data in 15 pregnant females (anile 15–28 y) and 9 healthy control subjects, but sample size constraints in the younger cohort precluded the authors from delineating possible age-related changes from those occurring as the outcome of the pregnancy itself (9).

Self-selected calcium intakes in the adolescents in the nowadays report averaged 30 ± ix mmol/d during the third trimester of pregnancy. Although these intakes are comparable with the 1997 adequate intake recommendation (32.v mmol/d), they are essentially college than intakes typical of nonpregnant adolescents (≈22.2 mmol/d) (24). This intake coupled with the improved efficiency of intestinal calcium absorption provided an average of xv.iii mmol (612 mg) Ca to offset urinary, endogenous fecal, and fetal calcium demands in these adolescents. As expected, significant increases in urinary calcium excretion occurred, which is consequent with the physiologic changes that occur during pregnancy in response to plasma volume expansion and an increased glomerular filtration rate (25). Assuming that endogenous fecal calcium losses exercise non change during pregnancy (9), average calcium retention was half dozen mmol (240 mg) in these adolescents. Because superlative rates of fetal skeletal accession during the 3rd trimester have been reported to range from 6 to 7.five mmol/d (25), the degree of calcium retention accomplished by these adolescents does not appear to be sufficient to support peak rates of fetal calcium accession and still allow for any appreciable amount of adolescent skeletal accretion.

In this group of pregnant adolescents, a 30-one thousand transfer of calcium to the fetus over a 266-d gestation period would correspond to 4% of the adolescents' average total-body calcium content. This additional requirement for calcium may take adversely affected total-trunk BMC in the early postpartum catamenia, every bit evidenced by the finding that full-body BMC was on average eight% lower than predicted in 33% (five/15) of the adolescents. Assuming that 32.2% of total-torso BMC reflects calcium (26), an viii% deficit in full-body BMC in these v adolescents would stand for with a net deficit of ≈54 yard Ca. Because nosotros do not have baseline bone density data, we are unable to ascertain how much of this deficit may have been apparent before pregnancy, nor tin can we ascertain the relative division of losses betwixt pregnancy and the early on postpartum flow. Despite the variability in the timing of the postpartum study, no significant relations existed between the time elapsed between the pregnancy and postpartum studies and either lumbar spine z scores or the magnitude of arrears in full-torso BMC across the 19–44-d range studied. Previous studies found significantly higher losses of trabecular os at the heel in adolescents who connected to grow over the course of pregnancy than in adult women (17). Similarly, significantly greater losses of BMC were reported at the distal left radius in lactating adolescents (anile ≤ 18 y) than in women anile > 18 y (19). Studies in adults found either nonsignificant losses in full-body BMC betwixt the postdelivery measure and that obtained afterward 2 mo of lactation (7) or significant losses in total-torso BMC subsequently half dozen mo of lactation (27).

In add-on to adolescents having lower-than-predicted total-body BMC, 33% of the adolescents were osteopenic or osteoporotic on the basis of their lumbar spine z scores. Higher dietary calcium intakes during pregnancy were significantly related to maternal lumbar spine z scores in the early postpartum period, and higher calcium intakes were significantly associated with improvements in estimated calcium residuum, which suggests that higher calcium intakes were protective against os loss over the course of pregnancy. In addition, adolescents with the highest calcium absorption during pregnancy had significantly greater deficits in lumbar spine bone mass, suggesting that despite maximal increases in intestinal calcium assimilation, sufficient substrate was non bachelor to prevent maternal bone loss at the lumbar spine. This hypothesis is consistent with the trend for urinary Due north-telopeptide concentrations (an indirect marker of bone resorption) to be higher in adolescents with higher fractional calcium absorption during pregnancy.

The potential competition for calcium required for both adolescent and fetal skeletal accession may adversely touch on both maternal bone density and fetal bone development. Nosotros recently found that depression calcium intake (every bit assessed by maternal dairy product intake at entry into prenatal care) was significantly associated with decreased fetal femur length in utero in a grouping of 350 pregnant African American adolescents (28). Other studies found that calcium supplementation (≤ ii g/d) significantly increased neonatal bone density in infants built-in to women with suboptimal calcium intakes (29).

Nosotros were unable to address potential racial differences in calcium absorption, hormone status, or os loss between the white and African American adolescents because of the limited size of our white cohort. Recruitment of pregnant white adolescents was severely hampered past a much higher prevalence of self-reported cigarette use during pregnancy in white adolescents, consequent with national information detailing a college prevalence of cigarette smoking in white than in African American adolescents (30). The caste of osteopenia axiomatic in the adolescents studied is of interest because most of the adolescents were African American, and the run a risk of osteoporosis is known to be substantially lower in black women than in white women (31). Moreover, although studies have reported college rates of calcium assimilation in postmenarcheal blackness than in white adolescents (32), the fractional calcium absorption observed in the significant African American adolescents in the present study was comparable with that reported for meaning developed white women (seven).

In decision, calcium assimilation in adolescents was significantly college during the third trimester of pregnancy than during the early postpartum menses. Thirty-3 percent of the adolescents had lumbar spine z scores that met the definition of osteopenia or osteoporosis in the early postpartum period. The relative partitioning of os loss at this site over the course of pregnancy and the early postpartum menstruation is not known. However, in these adolescents, increased calcium intake during pregnancy appeared to be protective against maternal loss of trabecular bone at the lumbar spine. More research is needed in adolescents to address the event of habitual calcium intake on maternal os loss during pregnancy. Moreover, longer-term studies are needed to address the magnitude of bone loss over a longer class of lactation and the ability to regain bone loss after the resumption of menses to ensure that early childbearing does not have long-term agin consequences on bone mineral acquisition and attainment of top bone mass.

Nosotros give thanks the adolescents who volunteered to participate in this study and the nursing staff of the PCRU. We also thank Dominicus Lee and Lily Liang for laboratory aid and Steven Abrams for advice regarding this projection.

KOO was the chief investigator of the written report and was responsible for the study design, data assay, and manuscript preparation. MSN and JM assisted with subject recruitment and tracking of the adolescents at Motherhood Center East. FRW was responsible for all calcium infusions and medical intendance over the inpatient study and assisted with the study design, data interpretation, and manuscript preparation. None of the authors had any financial or personal relationships with the sponsor of this research.

REFERENCES

i

Maynard

RA

.

Kids having kids.

Washington, DC

:

The Urban Found Press

,

1997

.

2

Ventura

SJ

,

Mathews

TJ

,

Hamilton

BE

.

Births to teenagers in the United States, 1940-2000

.

Natl Vital Stat Rep

2001

;

49

:

1

–

23

.

3

Curtin

SC

,

Martin

JA

.

Births: preliminary data for 1999

.

Natl Vital Stat Rep

2000

;

48

:

1

–

20

.

4

Bailey

DA

,

Martin

AD

,

McKay

HA

,

Whiting

Southward

,

Mirwald

R

.

Calcium accretion in girls and boys during puberty: a longitudinal analysis

.

J Os Miner Res

2000

;

xv

:

2245

–

50

.

v

Forbes

GB

.

Calcium accumulation by the human fetus

.

Pediatrics

1976

;

57

:

976

–

7

(letter of the alphabet)

.

six

Cantankerous

NA

,

Hillman

LS

,

Allen

SH

,

Krause

GF

,

Vieira

NE

.

Calcium homeostasis and bone metabolism during pregnancy, lactation, and postweaning: a longitudinal study

.

Am J Clin Nutr

1995

;

61

:

514

–

23

.

7

Ritchie

LD

,

Fung

EB

,

Halloran

BP

, et al.

A longitudinal report of calcium homeostasis during human pregnancy and lactation and after resumption of menses

.

Am J Clin Nutr

1998

;

67

:

693

–

701

.

8

Kent

GN

,

Price

RI

,

Gutteridge

DH

, et al.

The efficiency of intestinal calcium assimilation is increased in belatedly pregnancy only not in established lactation

.

Calcif Tissue Int

1991

;

48

:

293

–

5

.

nine

Heaney

RP

,

Skillman

TG

.

Calcium metabolism in normal human pregnancy

.

J Clin Endocrinol Metab

1971

;

33

:

661

–

70

.

10

Black

AJ

,

Topping

J

,

Durham

B

,

Farquharson

RG

,

Fraser

WD

.

A detailed assessment of alterations in bone turnover, calcium homeostasis, and bone density in normal pregnancy

.

J Bone Miner Res

2000

;

15

:

557

–

63

.

xi

Naylor

KE

,

Iqbal

P

,

Fledelius

C

,

Fraser

RB

,

Eastell

R

.

The upshot of pregnancy on bone density and bone turnover

.

J Os Miner Res

2000

;

15

:

129

–

37

.

12

Kolthoff

N

,

Eiken

P

,

Kristensen

B

,

Nielsen

SP

.

Bone mineral changes during pregnancy and lactation: a longitudinal cohort study

.

Clin Sci (Lond)

1998

;

94

:

405

–

12

.

13

Prentice

A

.

Calcium in pregnancy and lactation

.

Annu Rev Nutr

2000

;

20

:

249

–

72

.

14

Sowers

M

,

Wallace

RB

,

Lemke

JH

.

Correlates of forearm bone mass amongst women during maximal bone mineralization

.

Prev Med

1985

;

14

:

585

–

96

.

15

Play a trick on

KM

,

Magaziner

J

,

Sherwin

R

, et al.

Reproductive correlates of bone mass in elderly women. Written report of Osteoporotic Fractures Inquiry Group

.

J Bone Miner Res

1993

;

eight

:

901

–

viii

.

16

Lloyd

T

,

Lin

HM

,

Eggli

DF

,

Dodson

WC

,

Demers

LM

,

Legro

RS

.

Adolescent Caucasian mothers have reduced adult hip bone density

.

Fertil Steril

2002

;

77

:

136

–

twoscore

.

17

Sowers

MF

,

Scholl

T

,

Harris

L

,

Jannausch

1000

.

Bone loss in boyish and developed pregnant women

.

Obstet Gynecol

2000

;

96

:

189

–

93

.

eighteen

Chan

GM

,

Ronald

Northward

,

Slater

P

,

Hollis

J

,

Thomas

MR

.

Decreased bone mineral condition in lactating adolescent mothers

.

J Pediatr

1982

;

101

:

767

–

70

.

nineteen

Chan

GM

,

Slater

P

,

Ronald

N

, et al.

Bone mineral condition of lactating mothers of unlike ages

.

Am J Obstet Gynecol

1982

;

144

:

438

–

41

.

20

O'Brien

KO

,

Razavi

M

,

Henderson

RA

,

Caballero

B

,

Ellis

KJ

.

Bone mineral content in girls perinatally infected with HIV

.

Am J Clin Nutr

2001

;

73

:

821

–

vi

.

21

Yergey

AL

,

Abrams

SA

,

Vieira

NE

,

Aldroubi

A

,

Marini

J

,

Sidbury

JB

.

Conclusion of fractional assimilation of dietary calcium in humans

.

J Nutr

1994

;

124

:

674

–

82

.

22

Yergey

AL

,

Abrams

SA

,

Vieira

NE

,

Eastell

R

,

Hillman

LS

,

Covell

DG

.

Recent studies of human calcium metabolism using stable isotopic tracers

.

Can J Physiol Pharmacol

1990

;

68

:

973

–

half dozen

.

23

Yergey

AL

,

Vieira

NE

,

Covell

DG

.

Directly measurement of dietary fractional absorption using calcium isotopic tracers

.

Biomed Environ Mass Spectrom

1987

;

14

:

603

–

7

.

24

Establish of Medicine, Nutrient and Diet Board

.

Dietary reference intakes: calcium, magnesium, phosphorus, vitamin D and fluoride.

Washington, DC

:

National Academy Press

,

1997

.

25

Kovacs

CS

.

Calcium and bone metabolism in pregnancy and lactation

.

J Clin Endocrinol Metab

2001

;

86

:

2344

–

8

.

26

Ellis

KJ

,

Shypailo

RJ

,

Hergenroeder

A

,

Perez

1000

,

Abrams

S

.

Full torso calcium and os mineral content: comparing of dual-energy X-ray absorptiometry with neutron activation analysis

.

J Bone Miner Res

1996

;

11

:

843

–

8

.

27

Kalkwarf

HJ

,

Specker

BL

,

Bianchi

DC

,

Ranz

J

,

Ho

M

.

The issue of calcium supplementation on bone density during lactation and later on weaning

.

N Engl J Med

1997

;

337

:

523

–

8

.

28

Chang

SC

,

O'Brien

KO

,

Schulman Natanson

Thou

,

Caulfield

LE

,

Mancini

J

,

Witter

FR

.

Fetal femur length is influenced by maternal dairy product intake in pregnant African American adolescents

.

Am J Clin Nutr

2003

;

77

:

1248

–

54

.

29

Koo

WW

,

Walters

JC

,

Esterlitz

J

,

Levine

RJ

,

Bush

AJ

,

Sibai

B

.

Maternal calcium supplementation and fetal bone mineralization

.

Obstet Gynecol

1999

;

94

:

577

–

82

.

30

Griesler

PC

,

Kandel

DB

.

Ethnic differences in correlates of adolescent cigarette smoking

.

J Adolesc Health

1998

;

23

:

167

–

80

.

31

Looker

Ac

,

Johnston

CC

Jr,

Wahner

HW

, et al.

Prevalence of depression femoral bone density in older U.Due south. women from NHANES III

.

J Bone Miner Res

1995

;

x

:

796

–

802

.

32

Abrams

SA

,

O'Brien

KO

,

Liang

LK

,

Stuff

JE

.

Differences in calcium absorption and kinetics between black and white girls aged 5-16 years

.

J Bone Miner Res

1995

;

10

:

829

–

33

.

FOOTNOTES

2

Supported by NIH grant HD35191 and NCRR/GCRC grant RR00052.

© 2003 American Social club for Clinical Diet