title: Secular trend in age at menarche for women born between 1920 and 1979 in Rio de Janeiro, Brazil.
abstract: OBJECTIVE
  This article presents data on the secular trend in age at menarche for 1955 women from 16 to 76 years of age born between 1920 and 1979 and studied under the Nutrition and Health Survey conducted in the municipality of Rio de Janeiro, Brazil, in 1996.
  
  
  METHODS
  Age at menarche was defined by the retrospective method. Women were grouped according to decade of birth, and the trend was estimated using simple linear regression between age at menarche and year of birth for the following specific periods: 1920-1940, 1920-1960, 1960-1979 and 1920-1979.
  
  
  RESULTS
  Mean age at menarche decreased from 13.07 to 12.40 years when comparing the group of women born in the 1920s with the 1970s birth cohort, corresponding to a mean rate of -0.0123 years per year (p < 0.001). The downward trend was -0.0120 years per year (p > 0.05) for the 1920s, 30s and 40s, -0.0093 years per year (p < 0.05) for the period from 1920 to 1960, and -0.0224 years per year (p < 0.01) for the 1960s/70s.
  
  
  CONCLUSIONS
  The results suggest a secular trend in age at menarche. The literature points to such environmental variables as improved living conditions and expanded access to health services. Within this context, age at menarche could be used as a marker for social development.
authors.affiliation: Universidade Federal do Rio de Janeiro, Instituto de Nutrição Social e Aplicada, Departamento de Nutrição Social e Aplicada, RJ, Brazil. gkac@gbl.com.br
authors.forename: G
authors.initials: G
authors.lastname: Kac
authors.lastname: Auxiliadora de Santa Cruz Coel
authors.forename: G
authors.initials: G
authors.lastname: Velasquez-Melendez
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000375:Aging; D001938:Brazil; D005260:Female; D006801:Humans; D008572:Menarche / Q000502:physiology*; D008875:Middle Aged; D012189:Retrospective Studies