title: Quantitative responses of serum folate to increasing intakes of folic acid in healthy women.
abstract: OBJECTIVE
  Health authorities are advising people to increase folate intake and more foods are being fortified with folic acid. Estimation of dietary folate is difficult because nutrient data bases lack this nutrient in many countries and bioavailability is variable. To see if serum folate can be used to reflect effective folate intake, we have measured serum folate after healthy women had taken different doses of pure folic acid supplements in the nutritional range.
  
  
  METHODS
  A total of 20 volunteer subjects took part in one or more of three experiments, six of them took part in all three. In each experiment subjects took two different doses of folic acid, each for three weeks. Experiment (1) 100 micrograms then 1000 micrograms/d; experiment (2) 500 micrograms then 1500 micrograms/d; experiment (3) 1000 then 2000 micrograms/d. Serum folate was measured after overnight fast with a homogenous enzyme binding assay kit. In experiment (3) red cell folates were also measured.
  
  
  RESULTS
  It took three weeks' of the same supplement for serum folate to reach its full higher value. Mean serum folates of small groups of subjects were significantly higher with each higher dose of supplement. The biggest increase was for the first 100 micrograms that is in the range of intake from unfortified foods. The curve of serum folate against folic acid supplement intake shows that serum folate of groups of people, properly standardized, can provide a practical method for assessing adequacy or change of people's folate intake. Red cell folates were less responsive.
authors.affiliation: Department of Biochemistry G08, University of Sydney, NSW, Australia.
authors.forename: A S
authors.initials: AS
authors.lastname: Truswell
authors.forename: S
authors.initials: S
authors.lastname: Kounnavong
mesh_terms: D000284:Administration, Oral; D000328:Adult; D015415:Biomarkers / Q000097:blood; D005260:Female; D005492:Folic Acid / Q000008:administration & dosage* / Q000097:blood*; D006801:Humans
chemical_list: D015415:Biomarkers; D005492:Folic Acid