Interactions between serum leptin, the insulin‐like growth factor‐I system, and sex, age, anthropometric and body composition variables in a healthy population randomly selected
Authors: Gómez José Manuel , Maravall Francisco Javier , Gómez Núria , Navarro Miguel Angel , Casamitjana Roser , Soler Juan 
Published: March 2003

objective Leptin secretion is influenced by many factors and the GH/IGF axis plays an important role in the regulation of body composition, but the physiological interactions between leptin and the IGF‐I system remain unknown. In this study we investigated the relationship between leptin, the IGF‐I system, and sex, age, anthropometric and body composition variables in a group of healthy adults randomly selected.

design A cross‐sectional study.

patients The study included 268 subjects, representative of the whole population of the city of L’Hospitalet de Llobregat in sex and age distribution: 134 men aged 41·4 years, range 15–70 years; and 134 women, aged 40·7 years, range 15–70 years.

measurements Body mass index (BMI) was calculated, and body composition was determined by using a bioelectrical impedance analyser. Serum leptin concentrations were determined by using a radioimmunoassay (RIA). Serum total IGF‐I concentrations, after acid–ethanol extraction, were also measured by RIA. Serum free IGF‐I concentrations were determined by an enzymoimmunometric assay. Serum IGFBP3 concentrations were determined by RIA. Plasma basal TSH concentrations were determined by a specific electrochemiluminescence assay.

results In men the BMI was similar in all decades and waist/hip ratio increased in the last three decades. Fat‐free mass decreased by decade. We observed an increase in leptin in the fourth decade with a decrease in IGF‐I, free IGF‐I and IGFBP3 throughout the decades. Basal TSH showed an increase in the last two decades. In women, BMI, waist/hip ratio and fat mass increased significantly in the last decades. Leptin concentrations increased in the last decades and total IGF‐I, free IGF‐I and IGFBP3 decreased by decade without changes in basal TSH concentration. In men, there was a positive correlation between leptin and BMI, waist/hip ratio, total body water, fat‐free mass and fat mass, and these anthropometric and body composition variables showed a negative correlation with free IGF‐I and IGFBP3, without any correlation with total IGF‐I. In women, there was a positive correlation between leptin and BMI, waist/hip ratio, total body water, fat‐free mass, and fat mass, which showed a negative correlation with total IGF‐I and IGFBP3, without any correlation with free IGF‐I.

 In men, total IGF‐I was negatively correlated with waist/hip ratio without any correlation with the other variables and free IGF‐I was negatively correlated with BMI and waist/hip ratio, and IGFBP3 did not show any correlation. In women, total IGF‐I, free IGF‐I and IGFBP3 were negatively correlated with BMI, waist/hip ratio and fat mass. The multiple linear regression analysis produced a model that explained 60·5% of leptin variability in men and 40% in women. Notably, only age, BMI, fat mass and waist/hip ratio brought an independent significant contribution to leptin variability. The final model also explained 28·2% and 60·4% of total IGF‐I variability and 17·2% and 27·4% of free IGF‐I variability in men and women, respectively. Age and leptin contributed to free IGF‐I variability in men, and age and fat mass were significantly and independently associated with total IGF‐I in women.

conclusions In this well‐characterized population of controls randomly selected without chronic disease or drug administration and with biochemically confirmed euthyroidism, we found that both men and women had a significant correlation between leptin levels and the IGF‐I system, and anthropometric and body composition variables, but that leptin did not regulate the IGF‐I system, and that the IGF‐I system did not regulate leptin synthesis and secretion.