Ambulatory morning growth hormone concentrations increase in men and decrease in women with age

A remarkable 80-fold difference in median growth hormone (GH) values in young adult men and women was recently found in a study of sera taken in ambulatory state in the morning, after overnight fasting. In this study, the effect of ageing on morning ambulatory GH levels was investigated in 254 apparently healthy men, 21-75 years of age, and 40 women, 21-85 years. Furthermore, the effect of oestradiol on morning GH values was studied in 19 postmenopausal women, 51-79 years, treated with subcutaneous implants of 17beta-oestradiol (E2). The sera were analysed for GH, sex hormone-binding globulin (SHBG), E2, and in the men, also for testosterone (T). The morning GH levels increased (p<0.0001) with age in a group of 195 men of 41-75 years. After adjustment for age, an inverse correlation (p <0.05) was found between the levels of GH and free androgen index (T/SHBG) and a direct correlation between GH and SHBG. These relationships were more pronounced before the age of 60 than after. In the women, the GH levels decreased (p<0.01) with age and the gender difference of median values was reduced from 102-fold at younger age, 21-39 years, to 12-fold in elderly individuals, 60-75 years. In the E2-treated postmenopausal women, the morning GH values were similar to those of an untreated control group, indicating that the decrease with age in the morning GH levels in women is not a result of lower oestrogen levels alone. The gender difference in median ambulatory morning GH values decreased from 102-fold at a mean age of 25 years to 12-fold at a mean age of 68 years owing to opposite changes with age in men and women: an increase in men and a decrease in women.