Determinants of IGF1 and GH across the weight spectrum: from anorexia nervosa to obesity

Context: Chronic starvation is characterized by GH resistance, and obesity is characterized by decreased GH secretion. In both extremes, IGF1 levels may be low and androgen levels may be abnormal. Objective: To investigate the determinants of IGF1 and GH across the weight spectrum in women. Design: Cross-sectional study. Setting: Clinical research center. Study participants: In total, 32 women had participated in the study: 11 women with anorexia nervosa (AN), 11 normal-weight women, and 10 obese women of comparable mean age. Intervention: None. Main outcome measures: Pooled hourly overnight serum samples assayed for IGF1, GH, estradiol (E-2), testosterone, SHBG, insulin, free fatty acids, and trunk fat. Results: Free testosterone was higher in obese women and lower in women with AN than in normal-weight women, and was the only independent (and positive) predictor of IGF1 levels, accounting for 14% of the variability (P=0.032) in the group as a whole. This relationship was stronger when obese women were excluded, with free testosterone accounting for 36% of the variability (P=0.003). Trunk fat accounted for 49% of the variability (P<0.0001) of GH, with an additional 7% of the variability attributable to E-2 (P=0.042) in the group as a whole, but was not a significant determinant of GH secretion when obese women were excluded. Conclusions: Free testosterone is a significant determinant of IGF1 levels in women across the body weight spectrum. In contrast, GH secretion is differentially regulated at the extremes of the weight spectrum.