A prospective study of serum insulin-like growth factor I (IGF-I) and IGF-binding protein-3 in 942 healthy infants: associations with birth weight, gender, growth velocity, and breastfeeding.
BACKGROUND
Many aspects of hormonal regulation and mechanisms of normal infancy growth are poorly understood.


OBJECTIVE
The objective of this study was to establish the determinants of serum growth factor levels in infancy and their association with growth.


METHODS
A prospective, longitudinal, population-based birth cohort between 1997-2001 was studied.


METHODS
Study participants were 942 healthy appropriate weight for gestational age (AGA) infants (538 boys and 404 girls) and 49 small for gestational age (SGA) children (29 boys and 20 girls).


METHODS
INTERVENTIONS were anthropometrical measurements (0, 3, 18, and 36 months) and serum samples (3 months).


METHODS
Height, weight, and serum IGF-I and IGF-binding protein-3 (IGFBP-3) were the main outcome measures.


RESULTS
IGF-I levels showed no gender difference [boys, 92 ng/ml (confidence interval, 49, 162); girls, 91 ng/ml (47, 149); P = 0.50]. IGFBP-3 levels were significantly higher in females [2174 ng/ml (1295, 3330)] than in males [2103 ng/ml (1266, 3143); P = 0.04]. Infants receiving breast milk had lower IGF-I levels [90 ng/ml (48, 154)] than infants receiving formula [n = 62; 97 ng/ml (58, 165)] or both [n = 123; 94 ng/ml (48, 169); P < 0.001]. IGF-I and IGFBP-3 levels were positively associated with weight gain and height gain from birth to 3 months of age in AGA, but not in SGA, children. SGA children had significantly lower IGF-I [88.0 ng/ml (28, 145); P = 0.05] and IGFBP-3 [1835 ng/ml (1180, 2793); P < 0.001] levels than AGA children.


CONCLUSIONS
We found a significant, but weak, association between IGF-I and IGFBP-3 levels at 3 months and postnatal growth in AGA, but not SGA, children. Factors other than IGF-I must contribute to the regulation of normal postnatal growth, and these may differ between AGA and SGA children. IGFBP-3, but not IGF-I, showed a gender difference, which may reflect an influence of the postnatal activation of the pituitary-gonadal axis on binding protein levels.
Chellakooty
M
M
University Department of Growth and Reproduction, Section-GR 5064, Rigshospitalet, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
Juul
A
A
Boisen
K A
KA
Damgaard
I N
IN
Kai
C M
CM
Schmidt
I M
IM
Petersen
J H
JH
Skakkebaek
N E
NE
Main
K M
KM
D015415:Biomarkers / Q000097:blood / Q000378:metabolism; D001724:Birth Weight; D001942:Breast Feeding; D015331:Cohort Studies; D005260:Female; D006128:Growth / Q000502:physiology*; D006801:Humans; D007223:Infant; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008137:Longitudinal Studies; D008297:Male; D012016:Reference Values; D012727:Sex Characteristics
D015415:Biomarkers; D018972:Insulin-Like Growth Factor Binding Protein 3; D007334:Insulin-Like Growth Factor I