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Population-based reference values for IGF-I and IGF-binding protein-1: relations with metabolic and anthropometric variables

Population-based reference values for IGF-I and IGF-binding protein-1 (IGFBP-1) have been established. One hundred and one women and the same number of men, 20–70 years old, were randomly selected from the population registry in the community of Linköping. Participation rate was 67%. Venous blood was drawn in the fasting state. Serum IGF-I was measured by RIA after acid-ethanol extraction and IGFBP-1 was determined by ELISA. IGF-I levels did not differ between genders and the decline with age was similar in men and women (men: Y=366–3·28xage (years), r =–0·61, P<0·0001; women: Y=386–3·49xage, r =–0·57, P<0·0001, P=0·4 for difference in slope). There were negative correlations between IGF-I and plasma lipids and blood pressure in both genders, but none was independent of age. Serum angiotensin-converting enzyme activity correlated positively with IGF-I in men independently from age (r =0·21, P=0·01). The distribution of IGFBP-1 was positively skewed and it was higher in women than in men (5·9±4·8 µg/l and 4·0±3·3 µg/l respectively; Mann–Whitney, P=0·002). In men and in the women not taking oestrogen, IGFBP-1 correlated positively with age (Spearman rank correlation (Spearman): men: r=0·32, P=0·002; women: r=0·24, P=0·03). C-peptide correlated negatively (Spearman: men: r =–0·38, P=0·002; women: r =–0·49, P<0·000) and sex hormone binding globulin positively with IGFBP-1 (Spearman: men: r=0·50, P<0·0001; women: r =0·55, P<0·0001).

IGF-I declined with age while IGFBP-1, which is considered to modulate the free bioactive fraction of IGF-I, increased. This suggests that IGF-I activity might be even lower in elderly subjects than is accounted for by the low total IGF-I.

European Journal of Endocrinology 136 165–172