title: Response of serum and red blood cell folate concentrations to folic acid supplementation depends on methylenetetrahydrofolate reductase C677T genotype: results from a crossover trial.
abstract: METHODS
  By increasing blood folate concentrations, folic acid supplementation reduces risk for neural tube defect-affected pregnancies, and lowers homocysteine concentrations. We assessed response of red blood cell (RBC) and serum folate to folic acid supplementation, and examined association of response with the genetic polymorphism C677T of the methylenetetrahydrofolate NAD(P)H (MTHFR) gene.
  
  
  RESULTS
  Randomized, controlled, crossover trial with two folic acid supplement treatment periods and a 30-week washout period. The primary outcome is blood folate (serum and RBC) concentrations. Volunteers (n = 142) aged 18-69 were randomized to two of three doses (0, 200, and 400 μg) of folic acid for 12 weeks. Serum folate response depended on treatment period with significant responses to 200 μg seen only in the second treatment periods (4.4 ng/mL or 3.4 ng/mL). Additionally, serum folate increased as folic acid dose increased to 400 μg (p < 0.01) and response was greater after the washout period (8.7 ng/mL), than after a 6-week run-in (2.3 ng/mL). The differential change attributable to a daily supplement of 400 μg compared to 200 μg was 96.8 ng/mL; while the change attributable to 400 μg compared to 0 μg was 121.4. Increases in RBC folate concentrations with 400 μg occurred within MTHFR gene mutation (C677T); and in the African American group.
  
  
  CONCLUSIONS
  Serum folate concentration is responsive to modest increases in folic acid intake. RBC folate increases only with higher additional doses of folic acid supplementation, and this is true for each MTHFR C677T genotype.
authors: Department of Family and Preventive Medicine, School of Medicine, University of California San Diego, La Jolla, CA 92093, USA. c1anderson@ucsd.edu
authors: Cheryl A M
authors: CA
authors: Anderson
authors: Shirley A A
authors: SA
authors: Beresford
authors: Dale
authors: D
authors: McLerran
authors: Johanna W
authors: JW
authors: Lampe
authors: Samir
authors: S
authors: Deeb
authors: Ziding
authors: Z
authors: Feng
authors: Arno G
authors: AG
authors: Motulsky
mesh_terms: D000293:Adolescent; D000328:Adult; D001741:Black or African American / Q000235:genetics; D000368:Aged; D018592:Cross-Over Studies; D019587:Dietary Supplements; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism; D005260:Female; D005492:Folic Acid / Q000008:administration & dosage* / Q000097:blood*; D005838:Genotype; D006801:Humans; D008297:Male; D042965:Methylenetetrahydrofolate Reductase (NADPH2) / Q000235:genetics*; D008875:Middle Aged; D009154:Mutation; D055815:Young Adult
chemical_list: D005492:Folic Acid; C573423:MTHFR protein, human; D042965:Methylenetetrahydrofolate Reductase (NADPH2)