The Influence of Age on the 24-Hour Integrated Concentration of Growth Hormone in Normal Individuals*

Abstract

We examined changes in spontaneously secreted growth hormone with aging by studying the 24-h integrated concentration of GH (IC-GH) of 173 nonobese subjects (height, ≥5%; 7–65 yr of age). There was no significant difference in IC-GH on repeat testing of 13 men or in 23 women studied in the follicular and again in the luteal phase of the menstrual cycle. The level of IC-GH was strongly effected by age; children had the highest mean IC-GH, and there was a decline in IC-GH with increasing age after the second decade of life. The correlation of IC-GH with age was highly significant (r = 0.73; P < 0.0001). There was no difference in IC-GH between males and females when matched for age. The mean IC-GH at Tanner stage 5 of puberty (7.4 ± 2.0 ng/ml) was higher than that at stages 2–4 (5.7 ± 1.4; P < 0.0005) or that irl prepubertal children (5.8 ± 1.4; P < 0.001). Thus, age and pubertal status must be carefully considered when interpreting the IC-GH for patients suspected of having deficient or excessive secretion of GH.