Quantitative responses of serum folate to increasing intakes of folic acid in healthy women

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Abstract
Objectives: 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 µg then 1000 µg/d; experiment (2) 500 µg then 1500 µg/d; experiment (3) 1000 then 2000 µg/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 µg, 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. Sponsorship: S Kounnavong was in receipt of an Australian Agency for International Development Fellowship. Expenses were covered by the University of Sydney and its Nutrition Research Foundation. There was no conflict of interest.

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