title: Lead exposure is associated with a delay in the onset of puberty in South African adolescent females: findings from the Birth to Twenty cohort.
abstract: BACKGROUND
  One of the suggested, yet under-researched, causes of pubertal delay is lead exposure. In South Africa blood lead levels are generally higher than in resource-rich countries. Thus the effects of lead exposure on pubertal development may be significant.
  
  
  OBJECTIVE
  The objective of this study is to determine the association between lead exposure and pubertal development in adolescent females in the Birth to Twenty cohort (Bt20).
  
  
  METHODS
  Bt20 is a Johannesburg based birth cohort study that commenced in 1990 and includes 1682 girls. At 13 years of age venous blood samples were collected from 725 adolescent female participants for lead content analyses; of these, 712 had menarche data. Pubertal measurement was based on age of menarche and self-reported Tanner staging for pubic hair (n=684) and breast development (n=682).
  
  
  RESULTS
  The mean blood lead level for the sample was 4.9 microg/dl. Fifty percent had blood lead levels <5.0 microg/dl, 49% were > or = 5.0 microg/dl and 1% was >10.0 microg/dl. The average age of menarche was 12.7 years. At 13 years, 4% and 7% had reached Tanner stage 5 for pubic hair and breast development, respectively. Analyses showed that higher blood lead levels were associated with significant delays in the onset of puberty (p<0.001).
  
  
  CONCLUSIONS
  The study found that higher blood lead levels were associated with a delay in the onset of puberty, after adjustment for confounders. Lead exposure in resource-poor countries is generally higher compared to resource-rich countries and thus the effects of high blood levels have personal and public health significance.
authors.affiliation: Medical Research Council of South Africa, Environment and Health Research Unit, PO Box 87373, Houghton, 2041, Johannesburg, South Africa. Nisha.naicker@mrc.ac.za
authors.forename: Nisha
authors.initials: N
authors.lastname: Naicker
authors.forename: Shane A
authors.initials: SA
authors.lastname: Norris
authors.forename: Angela
authors.initials: A
authors.lastname: Mathee
authors.forename: Piet
authors.initials: P
authors.lastname: Becker
authors.forename: Linda
authors.initials: L
authors.lastname: Richter
mesh_terms: D000293:Adolescent; D002648:Child; D015331:Cohort Studies; D003710:Demography; D004781:Environmental Exposure / Q000032:analysis* / Q000706:statistics & numerical data; D004785:Environmental Pollutants / Q000097:blood*; D005260:Female; D006801:Humans; D007854:Lead / Q000097:blood*; D011627:Puberty / Q000097:blood*; D011628:Puberty, Delayed / Q000097:blood / Q000453:epidemiology*; D013019:South Africa
chemical_list: D004785:Environmental Pollutants; D007854:Lead