title: Seasonal variation of peripheral blood leukocyte telomere length in Costa Rica: A population-based observational study.
abstract: OBJECTIVE
  Peripheral blood leukocyte telomere length (LTL) is increasingly being used as a biomarker of aging, but its natural variation in human populations is not well understood. Several other biomarkers show seasonal variation, as do several determinants of LTL. We examined whether there was monthly variation in LTL in Costa Rica, a country with strong seasonal differences in precipitation and infection.
  
  
  METHODS
  We examined a longitudinal population-based cohort of 581 Costa Rican adults age 60 and above, from which blood samples were drawn between October 2006 and July 2008. LTL was assayed from these samples using the quantitative PCR method. Multivariate regression models were used to examine correlations between month of blood draw and LTL.
  
  
  RESULTS
  Telomere length from peripheral blood leukocytes varied by as much as 200 base pairs depending on month of blood draw, and this difference is not likely to be due to random variation. A moderate proportion of this association is statistically accounted for by month and region specific average rainfall. We found shorter telomere length associated with greater rainfall.
  
  
  CONCLUSIONS
  There are two possible explanations of our findings. First, there could be relatively rapid month-to-month changes in LTL. This conclusion would have implications for understanding the natural population dynamics of telomere length. Second, there could be seasonal differences in constituent cell populations. This conclusion would suggest that future studies of LTL use methods to account for the potential impact of constituent cell type.
authors.affiliation: Department of Medicine, Stanford University, Stanford, California, 94305.
authors.forename: David H
authors.initials: DH
authors.lastname: Rehkopf
authors.forename: William H
authors.initials: WH
authors.lastname: Dow
authors.forename: Luis
authors.initials: L
authors.lastname: Rosero-Bixby
authors.forename: Jue
authors.initials: J
authors.lastname: Lin
authors.forename: Elissa S
authors.initials: ES
authors.lastname: Epel
authors.forename: Elizabeth H
authors.initials: EH
authors.lastname: Blackburn
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging; D015415:Biomarkers / Q000378:metabolism; D003364:Costa Rica; D014644:Genetic Variation; D006801:Humans; D007962:Leukocytes / Q000166:cytology / Q000378:metabolism*; D008137:Longitudinal Studies; D008875:Middle Aged; D015999:Multivariate Analysis; D012044:Regression Analysis; D012621:Seasons; D059505:Telomere Homeostasis; D059506:Telomere Shortening
chemical_list: D015415:Biomarkers