BACKGROUND: Most previous studies concerning the relationship between IGF-I and age used assays measuring total IGF-I. Although free IGF-I is considered of greater biological relevance, little is known about its relationship with sex steroids levels in elderly healthy subjects. MEASUREMENTS: In s cross-sectional study of 218 healthy people (103 men, 115 women) aged 55-80 years we measured serum total and free IGF-I, IGFBP-1 and IGFBP3 levels and sex steroids. Free androgen index and free oestradiol index were used as an indicator for free oestradiol and free testosterone levels, respectively. RESULTS: Free IGF-I levels did not decline with age in the whole study population. Free IGF-I levels even increased in individuals above 70 years of age in comparison to those aged between 55 and 70 years (mean ± SE 0.106 ± 0.007 nmol/l vs. 0.086 ± 0.004 nmol/l, P=0.009). Total IGF-I and IGFBP-3 decreased with age (r=-0.20, P=0.005 and r=-0.24, P=0.001, respectively). Total IGF-I levels were positively related with free oestrogen index in both sexes. Free IGF-I did not relate to free oestrogen or androgen index. In women only, free IGF-I was related positively with DHEAS while IGFBP-1 was inversely correlated with DHEAS. CONCLUSIONS: Free IGF-I levels do not decrease with age and are even higher in individuals above 70 years. There was no relationship between free IGF-I and free androgen or oestrogen index in either gender. We hypothesize that higher free IGF-I levels in older persons may be the consequence of selective survival in the cohort: subjects with high free IGF-I levels may live longer. The absence of a relationship between free IGF-I levels and free androgen and oestrogen indices suggests that there is no direct interaction between the biological activity of circulating IGF-I levels and sex hormone production in a healthy ageing population.

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Journal Clinical Endocrinology
Janssen, J.A.M.J.L, Stolk, R.P, Pols, H.A.P, Grobbee, D.E, de Jong, F.H, & Lamberts, S.W.J. (1998). Serum free IGF-I, total IGF-I, IGFBP-1 and IGFBP-3 levels in an elderly population: Relation to age and sex steroid levels. Clinical Endocrinology, 48(4), 471–478. doi:10.1046/j.1365-2265.1998.00300.x