title: Lifestyle determinants of serum insulin-like growth-factor-I (IGF-I), C-peptide and hormone binding protein levels in British women.
abstract: OBJECTIVE
  This study aims to identify the lifestyle determinants of insulin-like growth factor-I (IGF-I) and its main binding proteins (IGFBPs), C-peptide, and sex hormone-binding globulin (SHBG) to help elucidate the mechanism through which lifestyle factors may affect cancer risk.
  
  
  METHODS
  This study is based on a sample of 292 British women, aged 20-70 years, whose lifestyle characteristics were assessed using a self-administered questionnaire and whose serum hormone concentrations were measured using immunoassays.
  
  
  RESULTS
  Age was a strong determinant of both IGF-I and IGFBP levels; women aged 65-70 years had significantly lower IGF-I and IGFBP-3 concentrations and significantly higher IGFBP-1 and IGFBP-2 concentrations than women aged 20-24 years. Body mass index (BMI) was not strongly associated with IGF-I, although women with a BMI of 26-27.9 kg/m2 had a higher IGF-I concentration compared with both lean (BMI <20 kg/m2) and obese (BMI 30+ kg/m2) women. However, obese women had a significantly higher C-peptide and IGFBP-3 concentration and a significantly lower IGFBP-1, IGFBP-2, and SHBG concentration compared with lean women. Increasing vigorous exercise was associated with a significantly lower C-peptide concentration and increasing leisure-time activity was associated with a significantly higher IGFBP-1 concentration. Other lifestyle factors such as job activity, smoking, and reproductive factors were not associated with any hormone.
  
  
  CONCLUSIONS
  Our data show that age is a major determinant of both IGF-I and its main binding proteins in women. BMI has strong effects on IGFBPs, C-peptide, and SHBG, but its effects on IGF-I remain unclear. The possible effect of physical activity on IGFBP-1 requires further investigation.
authors.affiliation: Cancer Research UK Epidemiology Unit, University of Oxford, Radcliffe Infirmary, Oxford, OX2 6HE, UK. naomi.allen@cancer.org.uk
authors.forename: Naomi E
authors.initials: NE
authors.lastname: Allen
authors.forename: Paul N
authors.initials: PN
authors.lastname: Appleby
authors.forename: Rudolf
authors.initials: R
authors.lastname: Kaaks
authors.forename: Sabina
authors.initials: S
authors.lastname: Rinaldi
authors.forename: Gwyneth K
authors.initials: GK
authors.lastname: Davey
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Key
mesh_terms: D000328:Adult; D000367:Age Factors; D015992:Body Mass Index; D002096:C-Peptide / Q000097:blood / Q000378:metabolism*; D005260:Female; D006801:Humans; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000097:blood / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000502:physiology*; D008019:Life Style; D008875:Middle Aged; D009043:Motor Activity; D009369:Neoplasms / Q000453:epidemiology* / Q000378:metabolism*; D012306:Risk; D012738:Sex Hormone-Binding Globulin / Q000032:analysis / Q000378:metabolism*; D006113:United Kingdom / Q000453:epidemiology
chemical_list: D002096:C-Peptide; D018970:Insulin-Like Growth Factor Binding Protein 1; D012738:Sex Hormone-Binding Globulin; D007334:Insulin-Like Growth Factor I