Introduction: Recombinant human IGF1 (rhIGF1) improves insulin sensitivity and glycaemic control when administered to people with diabetes. The effects of rhIGF1 on lipid metabolism in vivo are unclear.
Objectives: To determine the effects of rhIGF1/rhIGFBP3 administration on fasting lipids, non-esterified fatty acids (NEFA) and glucose homeostasis in recreational athletes. This study was part of a randomised, double-blind, placebo-controlled trial studying detection methods for IGF1 abuse.
Methods: The study received approval from the local ethics committee. 56 recreational athletes (age 1830 years, 30 males, 26 females) were randomly assigned to receive placebo, low dose rhIGF1/rhIGFBP3 complex (30 mg/day) or high dose rhIGF1/rhIGFBP3 complex (60 mg/day) by subcutaneous injection for 28 consecutive days. Variables measured before and immediately after the treatment period were: fasting lipids, NEFA, glucose, insulin and HbA1c. The homeostatic model assessment (HOMA-IR) was used to estimate insulin sensitivity. Intra-individual changes were assessed using paired t-tests.
Results: No significant changes in serum lipids were observed in the placebo group. In both women and men treated with rhIGF1/rhIGFBP3, there were significant reductions in fasting triglycerides (mean decrease 0.13±0.06 mmol/l, P=0.025 in women; 0.24±0.08 mmol/l, P=0.01 in men). In women, but not in men, there were significant increases in total cholesterol (mean increase 0.47±0.12 mmol/l, P=0.001), HDL (mean increase 0.16±0.03 mmol/l, P<0.001) and LDL (mean increase 0.37±0.1 mmol/l, P=0.001). No changes in cholesterol:HDL ratio or fasting NEFA were observed. Fasting insulin and HOMA-IR decreased in both women and men treated with rhIGF1/rhIGFBP3; there was also a significant decrease in HbA1c in women (mean reduction 0.3±0.1%, P<0.001) but not in men.
Conclusions: Fasting triglycerides decrease in recreational athletes after the administration of rhIGF1/rhIGFBP3 for 28 days; these changes are associated with increased insulin sensitivity. RhIGF1/rhIGFBP3 appears to have a more pronounced effect on lipid and glucose homeostasis in women than in men.