title: 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.
abstract: 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.
  
  
  METHODS
  A cross-sectional study.
  
  
  METHODS
  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.
  
  
  METHODS
  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.
authors.affiliation: Endocrinology Service, Ciudad Sanitaria y Universitaria de Bellvitge, L'Hospitalet de Llobregat, Barcelona, Spain. jmgs@csub.scs.es
authors.forename: José Manuel
authors.initials: JM
authors.lastname: Gómez
authors.forename: Francisco Javier
authors.initials: FJ
authors.lastname: Maravall
authors.forename: Núria
authors.initials: N
authors.lastname: Gómez
authors.forename: Miguel Angel
authors.initials: MA
authors.lastname: Navarro
authors.forename: Roser
authors.initials: R
authors.lastname: Casamitjana
authors.forename: Juan
authors.initials: J
authors.lastname: Soler
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D001823:Body Composition; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D020738:Leptin / Q000097:blood*; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D012737:Sex Factors; D013030:Spain; D018709:Statistics, Nonparametric; D013972:Thyrotropin / Q000097:blood
chemical_list: D018972:Insulin-Like Growth Factor Binding Protein 3; D020738:Leptin; D007334:Insulin-Like Growth Factor I; D013972:Thyrotropin