The impact of mandatory fortification of flour with folic acid on the blood folate levels of an Australian population

There is convincing evidence that an increased periconceptional intake of folate can reduce the incidence of neural tube defects in newborn infants.1,2 This has led to the introduction of a range of government-sponsored health promotion campaigns encouraging women of childbearing age to supplement their daily intake of folate, and in many countries has also led to new food standards which provide for fortification of some food products with folic acid.

After the introduction of voluntary fortification of selected foods with folic acid in Australia in 1995, there was a significant rise in the population’s blood folate levels and a reduction in the incidence of neural tube defects between 1996 and 2006.2,3 However, by 1999 there were still only 104 folic acid-fortified products available in Australia,4 and the impact of the voluntary fortification program fell short of what could be achieved with a universal fortification program. It was considered that mandatory fortification of flour would have a wider impact on blood folate levels and result in a further reduction in the incidence of neural tube defects.4

Since September 2009, Australian millers have been required to add folic acid to wheat flour used for breadmaking. Under Clause 4 (2) of Standard 2.1.1 of the Australian New Zealand Food Standards Code, this flour must now contain 2–3 mg of folic acid per kilogram.5 This should result in 0.135 mg of folic acid per 100 g of bread, which is the equivalent of about three slices and approximately half of the recommended daily intake of folate (0.2 mg).4

A large number of blood samples are regularly tested for serum and red blood cell (RBC) folate levels in diagnostic pathology laboratories. To determine the impact that the introduction of mandatory fortification has had on folate levels in an Australian population, we retrospectively reviewed serum and RBC folate levels for samples collected during the period 2007–2010 and analysed in a large public hospital laboratory.

Between April 2009 and April 2010, the prevalence of low serum folate levels decreased by 77% (from 9.3% to 2.1%) and the prevalence of low RBC folate levels decreased by 85% (from 3.4% to 0.5%) (Box). Our analysis of results for each April from 2007 to 2010 showed a marked decrease in low RBC folate levels after April 2009 (Box). The prevalence of low RBC folate levels among females of childbearing age (15–50 years) also decreased after April 2009 (Box), and in April 2010, there was only one sample from a female of childbearing age out of a total of 609 samples tested (0.16%) which had a low RBC folate level.

Between April 2009 and April 2010, there was a 31% increase in the mean serum folate level (from 17.7 nmol/L to 23.1 nmol/L; t = 9.3; P < 0.001) and a 22% increase in the mean RBC folate level (from 881 nmol/L to 1071 nmol/L; t = 8.7; P < 0.001) (Box). In the same period, the prevalence of serum folate levels > 45 nmol/L (the upper limit of assay detection in serum) increased from 6.6% to 12.8% (χ2 = 29.7; P < 0.001) and the prevalence of RBC folate levels > 2000 nmol/L (the upper limit of assay detection in RBCs) increased from 6.9% to 7.9% (χ2 = 12.0; P < 0.001).

An overall shift towards increased folate levels in the population was evident from analysing the distribution of serum folate levels between April 2009 and April 2010 (Box). Monthly mean serum and RBC folate levels increased gradually between April 2009 and April 2010. The greatest increase in mean serum folate levels was during September 2009 — the month that mandatory fortification was introduced (Box).

An evaluation of the effect of mandatory fortification of cereal-grain products with folic acid in the United States was reported in the National Health and Nutrition Examination Survey (NHANES) studies and showed a doubling of the mean serum folate level from 11.4 nmol/L to 26.9 nmol/L.6 Our study showed a 31% increase in the mean serum folate level by April 2010, even when the 77 patients with levels above 45 nmol/L were excluded. In 2008, the NHANES report showed that after mandatory fortification was introduced in the US, the prevalence in women of childbearing age of low RBC folate levels was 4.5%, and of low serum folate levels was 0.5%.7 In our study, by April 2010 the prevalences of low RBC and serum folate levels in all samples were 0.5% and 2.1%, respectively, and only one low RBC folate level (0.16%) was from a woman of childbearing age.

The population studied was not necessarily representative of the whole Australian population. The blood samples were obtained serendipitously from a population for whom a blood folate test was requested for the investigation of possible folate deficiency, and thus are likely to be biased towards low folate levels. In addition, different patients were studied before and after the introduction of mandatory fortification, and the samples would have included blood samples from patients with coeliac disease and patients on wheat-free diets. However, in view of the large number of samples studied, it is reasonable to assume that samples from similar groups of patients were collected at each interval. We do not know how many samples were from patients already taking a folate supplement, but previous studies suggest that excluding these patients would make little difference to our results.3 The low prevalence of folate deficiency in populations who consume fortified flour may lead to a future consideration of reducing the frequency of folate testing.8

While increased folic acid intake can reduce the incidence of neural tube defects, it cannot prevent all cases.9 Neural tube defects occur at a low incidence even in the babies of women with normal or high blood folate levels. Genetic and environmental factors can cause a “floor effect” for folate-preventable neural tube defects.9

In the US, mandatory fortification of cereal-grain products with folic acid was expected to increase the folate intake by 100 μg/day in women (and more in men), whereas in Australia it was expected that there would be a 250 μg/day increase in women’s intake after voluntary fortification was introduced.1,4 An RBC folate level of 906 nmol/L is considered to significantly reduce the risk of neural tube defects.10 It has been suggested that supplementing a usual diet with 400 μg of folic acid daily would result in RBC folate levels over 906 nmol/L in a majority of women.10 In the US, even after mandatory fortification was introduced, fewer than 10% of women reached this level, and the mean RBC folate level among women was 590 nmol/L.6 In our group of Australian patients, a much higher proportion of women (64%) had an RBC folate level of greater than 906 nmol/L in April 2010. The impact of mandatory fortification on the incidence of neural tube defects has still not been evaluated.

There is ongoing controversy regarding possible harmful effects of folic acid intake from fortified products, driven by conflicting reports regarding whether risk of cancer, heart disease and masking of vitamin B12 deficiency increase after folic acid supplementation.1,11 It is reassuring that the mean rise in RBC folate levels shown in the large group of patients we studied was only 22% and the prevalence of RBC folate levels over 2000 nmol/L only increased from 6.9% to 7.9%. These relatively minor overall increases in blood folate levels have led to an impressive reduction in the prevalence of folate deficiency in this Australian population.

Trends in serum folate* and red blood cell (RBC) folate† levels for 20 592 samples analysed in one Australian diagnostic pathology laboratory, 2007–2010‡

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* Reference range (RR), 7–25 nmol/L. † RR, 310–1000 nmol/L. ‡ Arrows indicate the introduction of mandatory fortification of flour used in breadmaking. § Bars indicate 95% confidence intervals.