Introduction To prevent neural tube defects (NTD) folic acid fortification of wheat and corn flour has been mandatory in Brazil since 2004. The purpose of this study was to examine the effect that folic acid fortification has had on serum folate levels and its contribution of total folate intake.

Methods Data were obtained from two 24 h dietary recalls from a population-based study (2008–2010) in São Paulo-Brazil for 297 participants who also had serum folate concentrations measured. Folate intake was obtained using the software program Nutrition Data System for Research. Descriptive statistics, Pearson's correlates, Kruskal-Wallis and Student's t-tests were performed using Stata (Version 10.0).

Results The reference range (5th–95 th percentiles) for the population after the introduction of folic acid fortification was 4.6–16.4 ng/ml for serum folate. The prevalence of low (<3 ng/ml) serum folate was 0.6%, while 1.4% of population exceed the limit value of 20 ng/ml. Synthetic folate (folic acid) contributed 51.3% [49.2 to 53.4 95% CI] of total folate intake. Both natural folate and synthetic folate did not correlate with folate serum concentrations (p>0.05), however participants in the highest serum folate tertile were older (p=0.001), and synthetic folate intake among adults and the elderly was less than the group aged <19 years (p=0.01).

Conclusion There was a very low risk of folate deficiency in the studied population; older participants had higher levels of serum folate and lower intake of synthetic folate. Participants with excessive serum folate concentrations after the folic acid mandatory fortification of flour were identified.