title: Gender and telomere length: systematic review and meta-analysis.
abstract: BACKGROUND
  It is widely believed that females have longer telomeres than males, although results from studies have been contradictory.
  
  
  METHODS
  We carried out a systematic review and meta-analyses to test the hypothesis that in humans, females have longer telomeres than males and that this association becomes stronger with increasing age. Searches were conducted in EMBASE and MEDLINE (by November 2009) and additional datasets were obtained from study investigators. Eligible observational studies measured telomeres for both females and males of any age, had a minimum sample size of 100 and included participants not part of a diseased group. We calculated summary estimates using random-effects meta-analyses. Heterogeneity between studies was investigated using sub-group analysis and meta-regression.
  
  
  RESULTS
  Meta-analyses from 36 cohorts (36,230 participants) showed that on average females had longer telomeres than males (standardised difference in telomere length between females and males 0.090, 95% CI 0.015, 0.166; age-adjusted). There was little evidence that these associations varied by age group (p=1.00) or cell type (p=0.29). However, the size of this difference did vary by measurement methods, with only Southern blot but neither real-time PCR nor Flow-FISH showing a significant difference. This difference was not associated with random measurement error.
  
  
  CONCLUSIONS
  Telomere length is longer in females than males, although this difference was not universally found in studies that did not use Southern blot methods. Further research on explanations for the methodological differences is required.
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authors.affiliation: School of Social and Community Medicine, University of Bristol, Canynge Hall, Bristol, UK. Electronic address: Y.Ben-Shlomo@bristol.ac.uk.
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mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012737:Sex Factors; D016615:Telomere / Q000502:physiology*
keywords: Epidemiology; Gender; Measurement methods; Systematic review and meta-analysis; Telomere length