title: A cohort effect on serum testosterone levels in Finnish men.
abstract: OBJECTIVE
  To investigate whether a population-level decline in serum testosterone exists in Finnish men. In comparison with other European populations, Finnish men have compared well in the studies of reproductive health (i.e. semen quality, incidence of cryptorchidism and testicular cancer); thus, we expected no significant cohort-dependent decrease in serum testosterone.
  
  
  METHODS
  We analysed serum levels of testosterone, gonadotrophin and sex hormone binding globulin (SHBG) in 3271 men representing different ages (25-74 years) and birth cohorts within three large Finnish population surveys conducted in 1972, 1977 and 2002.
  
  
  RESULTS
  Serum testosterone levels decreased (from 25.3 nmol/l in 25- to 29-year-old men gradually to 16.9 nmol/l in 70- to 74-year-old men), whereas SHBG and gonadotrophin levels increased with increasing age. In addition, a significant secular trend in testosterone (total and free), SHBG and gonadotrophin levels was observed with lower levels in more recently born age-matched men. Serum testosterone level decreased in men aged 60-69 years from 21.9 nmol/l (men born 1913-1922) to 13.8 nmol/l (men born 1942-1951). These decreases remained significant following adjustment for BMI. An age-independent birth cohort effect existed on reproductive hormones measured in the Finnish men. In concert with the lower free testosterone levels, we observed lower gonadotrophin levels, suggesting that while there may be detrimental changes at the gonad level, the hypothalamus-pituitary-axis is not responding appropriately to this change.
  
  
  CONCLUSIONS
  The more recently born Finnish men have lower testosterone levels than their earlier born peers. This study offers no explanation for this substantial recent adverse development.
authors.affiliation: Department of Physiology, Institute of Biomedicine, University of Turku, Kiinamyllynkatu 10, FI 20520 Turku, Finland. antti.perheentupa@utu.fi
authors.forename: A
authors.initials: A
authors.lastname: Perheentupa
authors.forename: J
authors.initials: J
authors.lastname: Mäkinen
authors.forename: T
authors.initials: T
authors.lastname: Laatikainen
authors.forename: M
authors.initials: M
authors.lastname: Vierula
authors.forename: N E
authors.initials: NE
authors.lastname: Skakkebaek
authors.forename: A-M
authors.initials: AM
authors.lastname: Andersson
authors.forename: J
authors.initials: J
authors.lastname: Toppari
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D015988:Cohort Effect; D015331:Cohort Studies; D005387:Finland; D005640:Follicle Stimulating Hormone / Q000097:blood; D006801:Humans; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D008875:Middle Aged; D012738:Sex Hormone-Binding Globulin / Q000378:metabolism; D013739:Testosterone / Q000097:blood*; D044465:White People
chemical_list: D012738:Sex Hormone-Binding Globulin; D013739:Testosterone; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone