¹Department of Human Nutrition, University of Otago, Dunedin, New Zealand

Correspondence: CM Skeaff, Department of Human Nutrition, University of Otago, PO Box 56, Dunedin, New Zealand. E-mail: murray.skeaff@stonebow.otago.ac.nz

Guarantor: CM Skeaff.

Contributors: CMS and TG had the original idea and obtained funds for the project. All authors were responsible for planning the study. BN and CA recruited subjects and were responsible for sample collection and laboratory analysis. All authors contributed to statistical analysis and writing of the report.

Received 19 March 2003; Revised 4 June 2003; Accepted 19 June 2003.

Abstract

Objective: Our aim was to determine if a once-a-week folic acid supplement increases women's red blood cell folate to concentrations (>905 nmol/l) that are associated with a low risk of bearing a child with a neural tube defect.

Design: Randomized control trial.

Setting: General community.

Subjects: In total, 114 nonpregnant women (18–40 y) volunteers, with red blood cell folate concentrations between 295 and 905 nmol/l at screening.

Interventions: Women were randomized to receive a once-a-week 2800 g folic acid supplement, a daily 400 g folic acid supplement or a daily placebo for 12 weeks.

Results: The mean (95% CI) red blood cell folate concentrations increased during the 12-week intervention from 608 (553–668) to 900 (828–978) in the weekly folic acid group (P<0.05) and from 615 (560–677) to 1053 (957–1158) nmol/l in the daily group (P<0.05) during the trial. At week 12, 49% of women ingesting the weekly folic acid supplement had red blood cell folate concentrations greater than 905 nmol/l compared to 74% of women ingesting the daily supplement.

Conclusions: A once-a-week 2800 g folic acid supplement can increase women's red blood cell folate to concentrations associated with a reduced risk of bearing a child with a neural tube defect, but is less effective than a 400 g daily supplement. Use of a weekly folic acid supplement over at least 12 weeks before conception by women of child-bearing age may prevent neural tube defects.

Funding: The Otago Medical Research Foundation (Laurenson Award). Healtheries (New Zealand) provided the supplements.