Effects of aging and sex on total plasma IGF-I levels were studied in 207 normal adults (103 males and 104 females), aged 21 to 80 years. Plasma IGF-I concentrations were measured by specific radioimmunoassay after extraction with acid-ethanol. Plasma IGF-I levels ranged from 50.8 to 480.6 micrograms/l with a mean (+/- SD) value of 200.7 +/- 81.9 micrograms/l in these normal adults. The mean plasma IGF-I levels were higher in females than in males in the second decade (332.6 +/- 63.9 vs 252.4 +/- 45.2 micrograms/l, p less than 0.01), whereas there was no sex difference in plasma IGF-I levels in elderly subjects. In both sexes, plasma IGF-I levels declined with age. In females, the slope of the regression line was much steeper in the young group (aged 21 to 40 years) than in the middle-aged and elderly group (aged 41 to 80 years) (y = -11.3x + 641.7, r = -0.538, p less than 0.005 and y = -1.97x + 289.3, r = -0.308, p less than 0.01). In males, plasma IGF-I linearly declined with age and the slope of the regression line (y = -2.36x + 322.2, r = -0.480, p less than 0.005) was not considerably different from that of the middle-aged and elderly group in females.
No takes yet. Share an insight, caveat, or question.
Yamamoto et al. (1991) studied this question.