Longitudinal analysis of the insulin-like growth factor system in African-American and European American children and adolescents.
BACKGROUND
IGF-I and its binding proteins influence growth, development, and disease risk. Studies have revealed ethnic variations in the IGF system.


OBJECTIVE
This longitudinal study was undertaken to test the hypothesis that the ethnic differences in the IGF system exist throughout the pubertal transition, and these differences are mediated at least in part by inherent differences in insulin dynamics.


METHODS
This was a longitudinal study. Annual evaluations were conducted for pubertal maturation, body composition, acute insulin response to glucose (AIRg), and reproductive-endocrine profile. Hormones and binding proteins were determined using standard assays, the AIRg during a frequently sampled iv glucose tolerance test, and body composition by dual-energy x-ray absorptiometry. Mixed model analyses were used to identify and characterize ethnic differences in the IGF system across the pubertal transition after adjusting for ethnicity, sex, age, maturation status, body composition, and reproductive hormones, and to identify the contribution of insulin to IGF binding protein (IGFBP)-1.


METHODS
Subjects included African-American (AA) and European American children (n = 162 at baseline) aged 7-16 yr, evaluated across the pubertal transition.


METHODS
Annual data on IGF-I, IGFBP-1, and IGFBP-3 were examined.


RESULTS
IGF-I was higher in AA children at pubertal stage 1 only (P < 0.001). However, IGFBP-3 and IGFBP-1 concentrations were lower in AAs through much of puberty (P < 0.05). The lower IGFBP-1 of AAs was in part explained by greater AIRg.


CONCLUSIONS
Our data suggest that the higher IGF-I and lower IGFBP-1 and IGFBP-3 levels in AAs as compared with European Americans during puberty suggest potential ethnic differences in circulating bioavailable IGF-I. In addition, higher AIRg in AAs may lead to greater bioavailable IGF-I. Whether these differences in the IGF system account for disparities in disease risk warrants further investigation.
Casazza
Krista
K
Department of Nutrition Sciences, 1675 University Boulevard, Room WEBB 415, University of Alabama at Birmingham, Birmingham, Alabama 35294-3360, USA. kristac@uab.edu
Higgins
Paul B
PB
Fernández
José R
JR
Goran
Michael I
MI
Gower
Barbara A
BA
D015502:Absorptiometry, Photon; D000293:Adolescent; D001741:Black or African American; D000375:Aging / Q000502:physiology; D001786:Blood Glucose / Q000378:metabolism; D001823:Body Composition / Q000502:physiology; D002648:Child; D005260:Female; D005951:Glucose Tolerance Test; D006801:Humans; D007328:Insulin / Q000235:genetics / Q000502:physiology; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000378:metabolism; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D008137:Longitudinal Studies; D008297:Male; D011627:Puberty / Q000502:physiology; D012098:Reproduction / Q000502:physiology; D012727:Sex Characteristics; D012741:Sexual Maturation; D013002:Somatomedins / Q000502:physiology*; D044465:White People
D001786:Blood Glucose; D007328:Insulin; D018970:Insulin-Like Growth Factor Binding Protein 1; D018972:Insulin-Like Growth Factor Binding Protein 3; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I
Clin Endocrinol (Oxf). 2005 Jul;63(1):94-102
15963068
Cancer Epidemiol Biomarkers Prev. 2006 Nov;15(11):2298-302
17119061
J Clin Endocrinol Metab. 2000 Feb;85(2):808-14
10690895
J Clin Endocrinol Metab. 1997 Jun;82(6):1923-7
9177407
J Lab Clin Med. 1998 Nov;132(5):383-9
9823932
Pediatr Res. 2005 Nov;58(5):850-4
16183814
Diabetes Obes Metab. 2008 Mar;10(3):198-211
18269635
Horm Res. 2006;65 Suppl 1:3-8
16508327
Calcif Tissue Int. 2002 Mar;70(3):146-52
11907710
J Clin Endocrinol Metab. 2002 Oct;87(10):4817-20
12364479
World J Urol. 2001 Aug;19(4):225-33
11550779
Diabetes. 1999 Aug;48(8):1515-21
10426367
J Pediatr. 1999 Sep;135(3):296-300
10484792
J Pediatr Endocrinol Metab. 2000 May;13(5):497-503
10803867
Stat Med. 1997 Oct 30;16(20):2349-80
9351170
BMJ. 1990 Jan 27;300(6719):230-5
2106931
Cancer Epidemiol Biomarkers Prev. 1999 Dec;8(12):1107-10
10613344
Pediatr Res. 1995 Aug;38(2):149-55
7478808
Annu Rev Med. 1968;19:283-300
4297619
J Clin Endocrinol Metab. 2006 Aug;91(8):3150-7
16720666
Urology. 2005 Sep;66(3):587-92
16140083
Acta Endocrinol (Copenh). 1992 May;126(5):381-6
1377853
Endocr Rev. 1997 Dec;18(6):801-31
9408744
Public Health Nutr. 2007 Jan;10(1):97-105
17212848
Am J Epidemiol. 2007 Sep 1;166(5):518-26
17602136
Growth Horm IGF Res. 2004 Jun;14(3):216-25
15125883
J Natl Cancer Inst. 2000 Oct 4;92(19):1592-600
11018095
J Pediatr. 1999 Sep;135(3):270-1
10484785
Carcinogenesis. 2007 Oct;28(10):2154-9
17724372
J Clin Endocrinol Metab. 2005 Mar;90(3):1483-8
15598684
Cancer Epidemiol Biomarkers Prev. 2004 Sep;13(9):1444-51
15342444
Oncology. 1999 Nov;57(4):330-40
10575321
Cancer Epidemiol Biomarkers Prev. 2005 Sep;14(9):2147-53
16172224
Urology. 1999 Jul;54(1):178-82
10414748
Circulation. 2002 Aug 20;106(8):939-44
12186797
J Biol Chem. 1991 Oct 5;266(28):18868-76
1717456
Pediatrics. 2002 Nov;110(5):911-9
12415029
J Pediatr. 2000 Dec;137(6):826-32
11113840