Association between Serum Insulin-Like Growth Factor-I Levels and Thyroid Disorders in a Population-Based Study

Abstract

There is current debate on whether serum IGF-I levels are associated with thyroid disorders. The aims of the present study were: 1) to investigate possible associations between serum IGF-I levels and thyroid disorders and 2) to analyze the role of serum IGF binding protein (IGFBP)-3 and TSH levels for these associations. This was a cross-sectional Study of Health in Pomerania. The study was conducted in the general population of northeast Germany. The study population comprised 3662 subjects (1746 women) without history of thyroid disorders. No interventions have been performed. Goiter and thyroid nodules were determined by ultrasound. Serum TSH levels less than 0.25 mIU/liter were considered decreased. Adjusted for major confounders and risk factors for thyroid disorders, subjects with serum IGF-I levels above the upper tertile had higher odds for goiter relative to subjects with serum IGF-I levels below the lower tertile [odds ratio (OR) 1.67; 95% confidence interval (CI) 1.24-2.26 in women; OR 2.04; 95% CI 1.55-2.68 in men]. A similar association was present for thyroid nodules in men (OR 1.64; 95% CI 1.17-2.32) and for decreased serum TSH levels in women (OR 1.65; 95% CI 1.00-2.69). Serum IGFBP-3 levels were not associated with thyroid disorders and did not represent effect modifiers for the association between serum IGF-I levels and the endpoints. We conclude that high serum IGF-I levels are associated with goiter. Whereas high serum IGF-I levels are also related to thyroid nodules in men, they are related to decreased serum TSH levels in women. Serum IGFBP-3 and TSH levels did not modulate these associations.