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Serum free IGF‐I, total IGF‐I, IGFBP‐1 and IGFBP‐3 levels in an elderly population: relation to age and sex steroid levels
Author(s) -
Joseph A M J L Janssen,
Ronald P. Stolk,
Huibert A. P. Pols,
Diederick E. Grobbee,
Frank H. de Jong,
S. W. J. Lamberts
Publication year - 1998
Publication title -
clinical endocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.055
H-Index - 147
eISSN - 1365-2265
pISSN - 0300-0664
DOI - 10.1046/j.1365-2265.1998.00300.x
Subject(s) - free androgen index , medicine , free testosterone , endocrinology , androgen , testosterone (patch) , igfbp3 , population , hormone , sex hormone binding globulin , growth factor , receptor , environmental health
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 a 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.