Global heterogeneity in folic acid fortification policies and implications for prevention of neural tube defects and stroke: a systematic review

Background

Folic acid (pteroylmonoglutamic acid) supplements are highly effective for prevention of neural tube defects (NTD) prompting implementation of mandatory or voluntary folic acid fortification for prevention of NTDs. We used plasma folate levels in population studies by country and year to compare effects of folic acid fortification types (mandatory or voluntary folic acid fortification policies) on plasma folate levels, NTD prevalence and stroke mortality rates.

Methods

We conducted systematic reviews of (i) implementation of folic acid fortification in 193 countries that were member states of the World Health Organization by country and year, and (ii) estimated population mean plasma folate levels by year and type of folic acid fortification. We identified relevant English language reports published between Jan 1, 1990 and July 31, 2023 using Google Scholar, Medline, Embase and Global Health. Eligibility criteria were observational or interventional studies with >1000 participants. Studies of pregnant women or children <15 years were excluded. Using an ecological study design, we examined the associations of folic acid fortification types with NTD prevalence (n = 108 studies) and stroke mortality rates (n = 3 countries).

Findings

Among 193 countries examined up to 31 July 2023, 69 implemented mandatory folic acid fortification, 47 had voluntary fortification, but 77 had no fortification (accounting for 32%, 53% and 15% of worldwide population, respectively). Mean plasma folate levels were 36, 21 and 17 nmol/L in populations with mandatory, voluntary and no fortification, respectively (and proportions with mean folate levels >25 nmol/L were 100%, 15% and 7%, respectively). Among 75 countries with NTD prevalence, mean (95% CI) prevalence per 10,000 population were 4.19 (4.11-4.28), 7.61 (7.47-7.75) and 9.66 (9.52-9.81) with mandatory, voluntary and no folic acid fortification, respectively. However, age-standardised trends in stroke mortality rates were unaltered by the introduction of folic acid fortification.

Interpretation

There is substantial heterogeneity in folic acid fortification policies worldwide where folic acid fortification are associated with 50-100% higher population mean plasma folate levels and 25-50% lower NTD prevalence compared with no fortification. Many thousand NTD pregnancies could be prevented yearly if all countries implemented mandatory folic acid fortification. Further trials of folic acid for stroke prevention are required in countries without effective folic acid fortification policies.

Funding

Medical Research Council (UK) and British Heart Foundation.

Spina bifida folate fortification in Brazil, update 2022: a cross-sectional study

INTRODUCTION

Despite improving maternal-child indicators in Brazil, congenital malformations are still the second cause of mortality in the first years of life. This work aims to compare statistical data before and after flour fortification with folic acid (FA) in Brazil.

METHODS

A cross-sectional Brazilian-population-based study compares the spina bifida (SB) rates pre- and post-fortification of the flour with folate. Data collected from the public database of the Live Birth Information System (SINASC/SUS) was performed. The period 1999-2004 (pre-fortification) was compared with 2005-2010 (post-maize and wheat fortification with FA), and another analysis comparing 2005-2010 and 2011-2020 (cassava flour fortification) was performed. The estimator was the prevalence ratio (PRR); the confidence interval selected was 95%. We used a random effects analysis model and inverse variance.

RESULTS

The review showed a tendency to decrease the PRR after flour fortification; however, there is no statistical significance between studies. DATASUS data analysis comparing 5 years before and 5 years after mandatory maize and wheat flour fortification demonstrated a rate ratio of 1.05 (95% CI 0.99-1.1; p = 0.075). Furthermore, comparing 10 years after additional cassava flour folate fortification, the rate ratio increased to 1.4 (95% CI 1.34-1.45; p < 0.01).

CONCLUSION

This study demonstrated an increase in SB after FA fortification. Possible explanations rely on national registry improvement, not fortified staple food, or further unidentified causes. Moreover, suggestions can be made for creating a mandatory registry for malformations, inspecting the concentrations of FA in the flour, and fortifying all food.

Folate status in women of childbearing age in the Urban Metropolitan Region of Chile: results from the National Health Survey 2016-2017

Objective:

To analyse serum folate levels in women of childbearing age in the Metropolitan Region (MR) of Chile.

Design:

Cross-sectional design as part of the 2016–2017 National Health Survey (Encuesta Nacional de Salud, ENS 2016–2017), using a household-based multistage stratified random sample. Serum folate levels measured by electrochemiluminescence immunoassay in fasting venous blood samples were classified as deficient (<4·4 ng/ml), normal (4·4–20 ng/ml) or supraphysiological (>20 ng/ml).

Setting:

The MR of Chile.

Participants:

Women of reproductive age (15–49 years, n 222) from the MR participated in the ENS 2016–2017.

Results:

The mean, median and range of serum folate were 14·2 (se 0·4), 13·9 and 2·1–32·2 ng/ml, respectively. Folate deficiency was detected in 0·9 % of women, while 7·0 % had supraphysiological levels of the vitamin. No significant effects of age, educational level, marital status, parity, smoking status or nutritional status on serum folate levels were detected by univariate or multivariate analyses. Intake of folic acid supplements showed a significant association with serum folate levels, but only 1·2 % of women used supplements.

Conclusions:

Folate deficiency in women of reproductive age living in the MR of Chile is almost inexistent according to the ENS 2016–2017, suggesting that the current population-wide mandatory folic acid fortification of flour is an effective and equitable measure to prevent folate deficiency. These results support the option of maintaining current folic acid fortification in Chile, particularly based on the low adherence to supplementation regimes evidenced in other populations.

Modelling the impact of mandatory folic acid fortification of bread or flour in Ireland on the risk of occurrence of NTD-affected pregnancies in women of childbearing age and on risk of masking vitamin B12 deficiency in older adults

PURPOSE

The rate of neural tube defects (NTDs) in Europe has remained similar since the 1990s despite folic acid supplement recommendations (400 µg/day) for women of childbearing age. Mandatory folic acid fortification of staple foods has proved effective for reducing the prevalence of NTDs in over 80 countries. This study estimated the impact of addition of folic acid to bread or flour in the Republic of Ireland on reducing the risk of occurrence of NTD-affected pregnancies and the possible risk of masking (undiagnosed) vitamin B₁₂ deficiency in older adults.

METHODS

Analyses were based on the Irish National Adult Nutrition Survey (2008-2010). Folic acid fortification was modelled using DaDiet© software. Estimates were made of the increase in average daily folic acid intake in women (18-50 years) and the risk of exceeding the tolerable upper intake level (UL) of 1000 µg for folic acid in adults over 50 years of age.

RESULTS

The fortification scenarios examined would reduce the risk of NTD-affected pregnancies by 8-32%, corresponding to an increase of 39-152 μg in the mean daily folic acid intake of WCBA. The risk of masking anaemia associated with vitamin B₁₂ deficiency in older adults would be negligible as the probability of exceeding the UL for folic acid, even by a small amount, is very low (≤ 0.2%).

CONCLUSIONS

These levels of addition of folic acid to bread or flour would effectively reduce the risk of NTDs while allowing safe consumption of folic acid at current levels from other fortified foods and supplements.

Effects of folic acid fortification on orofacial clefts prevalence: a meta-analysis

OBJECTIVE

Orofacial clefts (OFC) are the most prevalent craniofacial birth defect. Folic acid (FA) supplementation has been demonstrated as an effective intervention to reduce risk of OFC occurrence. However, the effect of mandatory FA fortification of wheat and/or maize flour on OFC prevalence has shown controversial results among countries adopting this policy. Thus, we performed a meta-analysis to synthesize the available evidence evaluating the global impact of this mandatory policy on OFC occurrence.

DESIGN

Literature search in conventional and grey medical/scientific databases showed fifteen studies considering OFC prevalence in pre- and post-fortification periods with FA. The effect of this policy was evaluated by computing relative risk (RR) and separating samples into total OFC, non-syndromic forms, cleft lip with or without cleft palate (CL/P) and cleft palate only (CPO).

RESULTS

We found a significant effect of FA fortification only on non-syndromic CL/P (RR=0·88; 95 % CI 0·81, 0·96), whereas neutral effects were detected for total OFC (syndromic plus non-syndromic) and CPO.

CONCLUSIONS

Our results may reflect the different aetiology of syndromic OFC with respect to non-syndromic forms and the CL/P related to CPO. Although the number of non-syndromic CL/P samples was lower than that for total OFC, the absence of both between-study heterogeneity and publication bias leads us to conclude that FA fortification may have beneficial effects on non-syndromic CL/P.

Prospective study of alcohol consumption and the risk of colorectal cancer before and after folic acid fortification in the United States

PURPOSE

To evaluate the influence of alcohol consumption on the risk of colorectal cancer according to folic acid fortification period in the United States.

METHODS

We evaluated the association between alcohol consumption and colorectal cancer by fortification period (before 1998 vs. after 1998) in 2 prospective cohort studies, the Nurses' Health Study (NHS) of women and the Health Professionals Follow-up Study (HPFS) of men, in which 2793 cases of invasive colorectal cancer were documented.

RESULTS

Alcohol consumption was associated with an increased risk of colorectal cancer. Among nonusers of multivitamins and/or folic acid supplements, the pooled multivariate relative risk for ≥30 g/d drinkers versus nondrinkers was 1.36 (95% confidence interval [95% CI], 1.09-1.70; P for trend, 0.02). The effect of alcohol consumption was slightly stronger in the prefolic acid fortification period (1980 NHS/1986 HPFS-1998) than in the postfortification period (1998-2008); the pooled multivariate relative risks for ≥30 g/d drinkers versus nondrinkers were 1.31 (95% CI, 1.00-1.71; P for trend, 0.10) in the prefortification period and 1.07 (95% CI, 0.69-1.65; P for trend, 0.67) in the postfortification period.

CONCLUSIONS

Folic acid fortification may attenuate the adverse effect of high alcohol consumption on the risk of colorectal cancer.