Age dependency of serum insulin - like growth factor (IGF)-1 in healthy Turkish adolescents and adults

Serum levels of insulin-like growth factor-1 (IGF-1) reflect endogenous growth hormone (GH) secretion in healthy subjects. Measurements of IGF-1 are useful for diagnosis and follow-up of patients with acromegaly and the diagnosis of GH deficiency in children.

To assess age dependency and normal ranges of serum IGF-1 levels in healthy Turkish population.

We therefore studied 272 healthy adolescents and adults between 15-75 years of age. None had diabetes or other endocrine disease or had received estrogen therapy.

Height, weight, body mass index (BMI) and waist-hip ratio were measured in all subjects. Serum samples were obtained during morning hours and IGF-1 was measured by radioimmunoassay.

The age-dependent reference range for serum IGF-1 concentrations was calculated by simple least linear regression analysis: the regression line represents the means with 95 percent confidence intervals. Correlation analysis was also done.

Ageing was negatively related to serum levels of IGF-1 (P= 0.0001, r=-0.931) with a mean decrease (youngest vs. oldest). IGF-1 levels increased during adolescence, with the highest mean values during puberty. After puberty, a subsequent decline in serum levels of IGF-1 was apparent. There were also a significant difference according to gender; females had significantly higher levels (357.909+/-219.167 mg/L) than males (307.962+/-198.41 mg/L) (P=0.012). IGF-1 levels were correlated with body height (P=0.001, r=0.223), body weight (P=0.002,r=-0.188) and BMI (P=0.039, r=0.128).

IGF-1 serum levels increase in adolescents with a peak in puberty, whereafter IGF-1 levels return to prepubertal levels.