title: Calculation of red blood cell folate steady state conditions and elimination kinetics after daily supplementation with various folate forms and doses in women of childbearing age.
abstract: BACKGROUND
  A maternal red blood cell (RBC) folate concentration > 906 nmol/L is thought to be optimal for lowering the risk of neural tube defects (NTDs) in pregnancy. Whereas the appearance of folate in RBCs has been followed during folic acid supplementation, data on elimination kinetics are not yet available.
  
  
  OBJECTIVE
  The aim of our investigation was to estimate the steady state conditions and elimination kinetics of folate in RBCs.
  
  
  METHODS
  Data from 2 randomized, placebo-controlled, double-blind intervention trials were used for kinetic modeling. These studies were performed to investigate the appearance of folate in RBCs in healthy women of childbearing age after different supplementation strategies (study 1: n = 69; 400 microg folic acid/d and 416 microg [6S]-5-methyltetrahydrofolate/d for 24 wk; study 2: n = 21; 800 microg folic acid/d for 16 wk).
  
  
  RESULTS
  For RBC folate concentrations, steady state conditions were not reached after 24 (study 1) and 16 (study 2) wk of folate supplementation. However, with the use of these data, we calculated the biological half-life (t(1/2)) of RBC folate to be approximately 8 wk. With the application of pharmacokinetic principles, steady state conditions for RBC folate should be reached after 40 wk (t(1/2) x 5).
  
  
  CONCLUSIONS
  With the use of pharmacokinetic principles, the appearance and elimination kinetics of RBC folate can be calculated on the basis of this t(1/2) value.
authors.affiliation: Institute of Nutrition and Food Sciences, Pathophysiology of Nutrition, University of Bonn, Bonn, Germany. k.pietrzik@uni-bonn.de
authors.forename: Klaus
authors.initials: K
authors.lastname: Pietrzik
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Lamers
authors.forename: Susanne
authors.initials: S
authors.lastname: Brämswig
authors.forename: Reinhild
authors.initials: R
authors.lastname: Prinz-Langenohl
mesh_terms: D000328:Adult; D003276:Contraceptives, Oral / Q000008:administration & dosage; D019587:Dietary Supplements; D004912:Erythrocytes / Q000737:chemistry*; D005260:Female; D005492:Folic Acid / Q000008:administration & dosage* / Q000097:blood*; D006801:Humans; D007700:Kinetics; D008954:Models, Biological; D009436:Neural Tube Defects / Q000517:prevention & control
chemical_list: D003276:Contraceptives, Oral; D005492:Folic Acid