It is known that the growth process is related to an individual's life-span, but the role of growth hormone (GH) secretion in human ageing remains unknown.
This study has focussed on the influence of GH on ageing parameters and on its relationship with human longevity.
To deal with the first issue, we compared ageing parameters of young (up to 39) and old (over 70) individuals having similar insulin-like growth factor-1 (IGF-1) blood levels. For the second one, the decline in IGF-1 levels was studied comparing its behaviour in the first half with that in the second half of adult life. The latter represents the period of life in which mortality progressively increases. Two hundred and five healthy individuals were chosen as subjects, well distributed by gender and age (between 19 and 93 years).
Old males with IGF-1 levels similar to young ones do not show the age-dependent decrease in serum testosterone and lean body mass, nor the increase in fat body mass. Other hormone-metabolic and nutritional parameters do not reveal any change compared with the results of all individuals. In females, the results do not allow to assume any IGF-1 influence. The behaviour of the linear regression in the second half of adult life of males, which becomes flat because old men having low IGF-1 blood levels die earlier, is consistent with these results. This effect, which is supported by predictive analysis, is not observed in females, i.e. the IGF-1 level declines in the second half of the women's adult life are only a little flatter than in the first half. Finally, extrapolating the regressions obtained in the first half of adulthood, the age at which the curve crosses the x-axis is 110 years for males and 132 for females.
The presented study of IGF-1 levels suggests that the GH secretion in adulthood plays a determinant role not only for some regressive manifestations, but also for life potential.