title: Thyroid hormones and erythrocyte indices in a cohort of euthyroid older subjects.
abstract: OBJECTIVE
  Hypothyroidism is associated with normocytic anaemia. Indeed, a limited number of studies have shown significant associations between free thyroxin (T4) and erythrocyte indices. These studies did not include vitamin B12, folic acid, iron and renal function in the analyses. We therefore studied the association between thyroid hormones and erythrocyte indices in a population-based cohort of older euthyroid subjects, with adjustment for major confounding parameters.
  
  
  METHODS
  Data, including thyroid hormones and erythrocyte indices, are from the Longitudinal Aging Study Amsterdam (LASA), an ongoing cohort study on predictors and consequences of changes in health in the ageing population in the Netherlands. Multivariable linear regression analyses were applied to study the cross-sectional associations between free T4, thyroid stimulating hormone (TSH) and erythrocyte indices (haemoglobin content, haematocrit, mean cell volume (MCV) and erythrocyte count) in a euthyroid sub-sample. The final models were adjusted for vitamin B12, folic acid, iron levels and renal function.
  
  
  RESULTS
  In 708 euthyroid older subjects, an increase of 5pmol/L free T4 was associated with a mean increase of 0.12mmol/L or 0.19g/dL of haemoglobin, 0.068 10(12)/L erythrocytes and 0.006L/L haematocrit (P=0.007, P=0.005, P=0.001, respectively). Free T4 was not significantly associated with MCV (P>0.05). TSH appeared not to be associated with any of the erythrocyte indices (all P>0.05).
  
  
  CONCLUSIONS
  In a cohort of older subjects, free T4, but not TSH, was associated with erythrocyte indices, confirming the role of thyroid hormones in the regulation of erythropoiesis.
authors.affiliation: Department of Clinical Chemistry, Haematology & Immunology, Medical Centre Alkmaar, Alkmaar, The Netherlands. roger@schindhelm.nl
authors.forename: Roger K
authors.initials: RK
authors.lastname: Schindhelm
authors.forename: Edwin
authors.initials: E
authors.lastname: ten Boekel
authors.forename: Nathalie E
authors.initials: NE
authors.lastname: Heima
authors.forename: Natasja M
authors.initials: NM
authors.lastname: van Schoor
authors.forename: Suat
authors.initials: S
authors.lastname: Simsek
mesh_terms: D000368:Aged; D000375:Aging / Q000502:physiology*; D004906:Erythrocyte Count; D004909:Erythrocyte Indices; D005260:Female; D006400:Hematocrit; D006801:Humans; D016014:Linear Models; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D013223:Statistics as Topic; D013961:Thyroid Gland / Q000502:physiology*; D013963:Thyroid Hormones / Q000097:blood*; D013972:Thyrotropin / Q000097:blood*
chemical_list: D013963:Thyroid Hormones; D013972:Thyrotropin