Growth hormone and the aging male

Abstract

Growth hormone (GH) exerts a crucial role in promoting somatic growth. In addition, GH constitutes a major regulator of body composition, bone and muscle metabolism, and cardiac function, and actually acts as a prime modulator of fuel metabolism. GH secretion is maximal during puberty. Thereafter, GH secretion falls in young adulthood to less than half the values achieved in mid- to late puberty. This decline is exponential, with a t1/12 of approximately 7 years, and is essentially complete by the beginning of the fifth decade. The origin of this decrease is likely to be multifactorial but the underlying mechanisms remain largely speculative. Since aging and ‘true’ GH deficiency due to pituitary disorders are associated with similar somatic features, it has been suggested that in older healthy subjects, these features result from relative GH-insulin-like growth factor-I (IGF-I) deficit and represent a syndrome that has been named somatopause. So far, however, the causal link between these somatic features and decreased GH secretion has not been proven. Therefore, the question remains as to whether the aim of restoring GH levels to the normal young range is legitimate. If that was the case, experimental approaches which might mimic natural GH secretory patterns and improve sleep quality, such as GH secretagogues, would appear more promising than GH administration, and futher clinical trials should be peformed in men 40–60 years old.