To the Editor: With the recognition that supplements of folate given early in pregnancy can reduce the incidence of neural tube defects,1,2 Australian manufacturers were allowed voluntary food fortification with folate from 1995, and these foods subsequently became available from August 1996. We assessed the impact of this fortification by comparing the results of assays of serum folate, a sensitive index of folate intake, before and after the introduction of folate-fortified foods.

Data were available for serum folate samples assayed by the chemiluminescence method (Chiron Healthcare Pty Ltd, Scoresby, Victoria) at our laboratory in Melbourne. Quality assurance data indicated no analytical drift, and external proficiency testing yielded satisfactory results throughout the period under study.

A total of 20 506 samples from women aged 14–45 years, the target group for supplementation, and 5528 samples from men of the same age group were assayed during 1993–2000. The results for the years 1993–1996, before fortification, where sample numbers were relatively small, were pooled. The results were analysed by Bhattacharya plot, eliminating the effect of outlier values,3 mindful of the limitations of extrapolating data derived from clinical material to the community. The mean values are shown in the Box. In both groups there was a small incremental rise in mean serum folate concentrations, and a fall in the prevalence of low values, after the introduction of fortification. The mean value of 14.0 nmol/L for women in 1993–1996 increased by about 19% to 16.7 nmol/L in 2000. The percentage of low values decreased from 8.5% to 4.1% over that period. Although it is possible that the increase in serum folate concentration reflects dietary education and use of folate supplements in women of reproductive age rather than food fortification specifically, parallel changes were also observed in men.

In the United States, folate fortification of all enriched cereal grain products was mandated from January 1998. This led to a dramatic increase of 250% in mean folate levels in women aged 15–44 years,4 and an increase of 50% in the median values (uncorrected for outliers) for men, women and children of all ages submitted for clinical evaluation.5 By comparison, the increase in folate levels in Australia has been very small. We conclude that to obtain a significant increase in folate intake in the community by food fortification, a policy of mandatory rather than voluntary fortification is required.