Consumption of folic acid fortified foods among Hispanic women of reproductive age in the US: a systematic review

Abstract

Background

In 1998, the United States (US) implemented mandatory folic acid fortification of enriched cereal grain products (ECGP) to prevent neural tube defects (NTD) in newborns. NTD rates remained highest among Hispanic births. Voluntary fortification of corn masa flour was approved in 2016, without improvement in NTD rates. This review aims to understand folic acid consumption among Hispanic women in the US before and after voluntary fortification.

Methods

A systematic search was conducted in PubMed, Embase, and Scopus from inception to September 2024 using the keywords folic acid, Hispanic Americans, and fortification. Study designs included descriptive, cross-sectional, and observational cohort. Studies in any language reporting the consumption of folic acid fortified foods among Hispanic women of reproductive age in the US were eligible. Study variables were compared to non-Hispanic White (NHW) women when available. Findings were summarized descriptively.

Results

Of 446 publications, eight studies (n = 20,123) met inclusion criteria. All studies reported on folic acid fortified foods, four characterized folic acid intake and acculturation factors, three quantified red blood cell (RBC) folate concentrations, and two described NTD rates. Hispanic women consumed grains, cereals, bread, flour, pasta, and corn masa flour. Most Hispanic women obtained folic acid from ECGP only. Hispanic women consumed more dietary folic acid than NHW women pre-voluntary fortification (406–456 µg (mcg) versus 349 mcg daily, p < 0.001) but less total folic acid when supplements were included (244 mcg versus 332 mcg daily, p < 0.05). Monolingual Spanish-speakers had the lowest total intake (224 mcg daily, p < 0.05). RBC folate concentrations were lower among Hispanic women compared to NHW women pre-voluntary fortification (963 nmol per liter (nmol/L) versus 1043 nmol/L) but showed no improvement post-fortification. Voluntary fortification did not significantly increase folic acid intake or reduce the proportion with inadequate intake; however, monolingual Spanish-speakers demonstrated higher intake and RBC folate concentrations. NTD rates remained similar between Hispanic (7.5/10,000 live births) and NHW women (7.1/10,000 live births) post-fortification. The certainty of evidence, assessed using the Grading of Recommendations, Assessment, Development, and Evaluations framework, ranged from low to very low across outcomes.

Conclusions

There is a paucity of literature to describe the rate, influencing factors, and prevalence disparities in NTD among Hispanic women living in the US despite its public health importance. This review provides a current summary on the disparities in folic acid intake and NTD rates between Hispanic and NHW women, and the effectiveness of voluntary fortification targeting populations at higher risk. Research initiatives investigating the factors influencing these disparities and future targeted interventions are necessary.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-025-22407-x.

Background

Neural tube defects (NTD) are defined as severe birth defects of the central nervous system resulting from the failure of the neural tube to completely close during embryonic development [1]. The current global prevalence of NTD is around 0.2% [2]. The main preventative measure against NTD, specifically anencephaly and spina bifida, is folate supplementation in women of reproductive age. Folate supplementation has been shown to prevent approximately 72% of NTD [3]. However, a 2007 survey of women of reproductive age (18–45) from the United States (US) demonstrated that while 81% of all respondents were aware of folic acid, only 12% recognized that folic acid should be taken before pregnancy to prevent birth defects, such as NTD [4]. In the same survey population, only 40% of all respondents reported taking a daily supplement containing folic acid, with 38% of Hispanic women reporting lower consumption compared to White respondents (40%).

The current recommendation for daily folate (vitamin B9) intake for women of reproductive age is approximately 400 µg (mcg) per day of folic acid for at least one month preconception and continue three months into pregnancy [5, 6]. While major dietary sources include green leafy vegetables, citrus fruits, liver, wheat bread, and legumes, disparities in access to these products have persisted across the American population with around 18.6% of women of reproductive age from 2011–2016 being folate insufficient [7, 8].

The Food and Drug Administration’s (FDA) 1998 implementation of mandatory folic acid fortification in enriched cereal grain products (ECGP) resulted in a 19% decline in the birth prevalence of NTD by December 1999, becoming one of the top 10 public health achievements in the US during the twenty-first century [9, 10]. Despite this success, Hispanic women remained more likely to give birth to a child with a NTD compared to non-Hispanic White (NHW) women [11, 12]. Rates of spina bifida remained disproportionately elevated in Hispanic births post-fortification, 0.7% in Hispanic births compared to 0.4–0.6% in non-Hispanic births [13]. There have been various proposed explanations for this persisting disparity, such as limited awareness regarding the role of folic acid in preventing NTD, cultural and socioeconomic influences, and acculturation [14–16]. Acculturation refers to the process by which individuals or groups adopt the attitudes, values, customs, beliefs, and behaviors of another culture [17]. Given that approximately one-third of the Hispanic population in the US consists of immigrants, it is important to consider the role of acculturation in shaping dietary choices and behaviors [18, 19]. Acculturation is commonly measured by factors such as language proficiency and time spent in the US [18]; several studies have demonstrated an inverse relationship between acculturation and healthy dietary patterns [20–22]. This relationship suggests that acculturation may play an important role in influencing food choices that contain varying concentrations of folic acid. The downstream consequence may alter the risk of developing an NTD in reproductively active women, but this has not been fully evaluated.

When examining cultural dietary influences specific to this population, one possible explanation for the disparity in NTD rates is the exclusion of corn masa flour from mandatory fortification measures. Corn masa flour is a significant dietary staple in Hispanic communities in the US [2]. This prompted the FDA to enact regulations in 2016 facilitating the voluntary fortification of corn masa flour with folic acid [2]. While the FDA’s strategic extension was presented as a plausible solution to enhance folic acid accessibility within the Hispanic community, its efficacy remains a subject of ongoing debate. A study assessing NTD rates in predominantly Hispanic zip codes before and after the FDA’s 2016 announcement found no statistically significant reductions in the risk of NTD [23]. In a parallel investigation, researchers surveyed folic acid fortification and concluded that only ~ 7% (3/43) of the corn masa flour products were fortified [2]. This suggests that despite the extension of fortification to corn masa flour, Hispanic women still face challenges in adopting and integrating folic acid into their diets. This systematic review aims to identify the state of folic acid consumption, acculturation factors associated with low intake, and the risk and prevalence of disease. We ultimately hope that this information can be used to propose recommendations to increase folic acid consumption and decrease the incidence of NTD in this population.

Methods

Search strategy

A systematic review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines to determine the status of folic acid consumption among Hispanic women of reproductive age in the US [24]. PubMed MEDLINE (National Library of Medicine), Embase (Elsevier), and Scopus (Elsevier) were searched from inception on September 9, 2024, using keywords associated with folic acid, Hispanic Americans, and fortification (see Supplementary Table 1, Additional File 1 for a full list of search terms). No restrictions on language, publication date, or article type were applied. The study protocol was retrospectively registered in Open Science Framework Registries and a copy can be requested by contacting the corresponding author [25].

Study selection

All articles were imported into EndNote for initial deduplication. The remaining articles were then imported into Rayyan (http://rayyan.qrci.org) for a final round of deduplication and screening. Articles progressing to full-text review were screened for final inclusion based on the following prespecified inclusion criteria (Supplementary Table 2, Additional File 1): (1) published in or translated to the English language, (2) published at any date, (3) discussion of folic acid fortified foods consumed by women of reproductive age who identify as Hispanic in the US, and (4) discussion on the outcomes of folic acid fortified foods consumed. During both stages of screening, all articles were screened independently by two reviewers (NV and SA). Any disagreement regarding the inclusion of an article was resolved by a third person (KB).

Data extraction

For included studies, data was extracted independently by NV and SA. Extracted data included bibliographic data, study design, number of participants, and outcomes. The primary study variable was the proportion or rate of consumption of folic acid fortified foods. Only studies that reported consumption of foods that can be fortified with folic acid such as ECGP and corn masa flour were included. ECGP are foods made from wheat, rice, oats, cornmeal, barley, or other cereal grains that are fortified with additional nutrients [26]. Wang and colleagues included corn masa flour under ECGP in the years after the voluntary fortification of corn masa flour [27, 28]. Ready-to-eat cereals (RTE) are cereal grain products that do not require further cooking in the home such as breakfast cereals and are classified with ECGP [29]. Secondary variables were acculturation factors for folic acid intake, red blood cell (RBC) folate concentrations, and NTD prevalence if reported. Acculturation factors are characteristics that influence an individual’s integration into a new cultural environment, including language spoken at home, country of origin, and length of time residing in the US [18]. RBC folate concentrations were measured in nanomoles per liter (nmol/L) using a microbiologic assay in the National Health and Nutrition Examination Survey (NHANES) and transformed and analyzed as described by Tinker et al. and Wang and colleagues [27, 28, 30]. Suboptimal RBC folate concentrations were defined as concentrations less than 748 nmol/L, a threshold commonly used in assay-adjusted analyses using NHANES data to estimate NTD risk, corresponding to an elevated risk of NTD, defined as less than nine NTD per 10,000 births [27, 28, 30].

When available we also included data among NHW women for comparison. We defined Hispanic as an ethnic group of individuals who self-identify as Hispanic or Latino, while NHW was defined as individuals who self-identified as White in terms of race and do not identify as Hispanic or Latino in terms of ethnicity. These definitions are consistent with those used by the US Census Bureau [31]. In instances where specific Hispanic subgroups, such as Mexican Americans (MA), were reported, we included them as they fall within the broader Hispanic category.

Study risk of bias and certainty of evidence assessments

The risk of bias for all outcomes reported by the included studies was assessed using the Risk of Bias in Non-randomized Studies-of Exposure (ROBINS-E) tool [32]. The ROBINS-E tool evaluates seven bias domains: (1) confounding, (2) measurement of the exposure, (3) selection of participants into the study or into the analysis, (4) post-exposure interventions, (5) missing data, (6) measurement of the outcome, and (7) selection of the reported result. Each domain and the overall risk of bias was rated as low risk of bias, some concerns, high risk of bias, and very high risk of bias. The overall risk of bias was determined by the highest risk of bias judgment across any domain. The certainty of evidence for all outcomes was assessed using the Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) framework [33]. The certainty of evidence was rated as very low, low, moderate, and high. The certainty of evidence could be rated down for risk of bias, imprecision, inconsistency, indirectness, or publication bias and could be rated up for large magnitude of effect, evidence of a dose–response gradient, or all reasonable confounding would decrease magnitude of effect.

For all studies, the risk of bias and certainty of evidence were independently assessed by two reviewers (NV and SA). Disagreements were resolved through consensus by a third reviewer (KB).

Data synthesis

The extracted data were synthesized descriptively and presented in tables and narrative text to summarize and highlight key findings across studies. Meta-analysis and pooling of estimates were not conducted due to heterogeneity in study designs (e.g., cohort versus (vs.) cross-sectional vs. descriptive), outcome definitions (e.g., percentage of women consuming a source vs. contribution to intake), and overlapping datasets (e.g., studies using similar NHANES data). The decision to forgo pooling of estimates was also influenced by the differences in risk of bias. Thematic synthesis was not applied because only one study reported qualitative data on acculturation factors and cultural dietary practices. Instead, qualitative findings were summarized narratively.

Results

A total of 730 articles were identified from three databases: PubMed (n = 153), Embase (n = 259), and Scopus (n = 318). Through the deduplication process, 284 duplicate articles were removed. The remaining 446 articles were screened by title and abstract, of which, 17 met the full-text review criteria. Eight articles were included in this review (see Fig. 1 for PRISMA full-text selection flowchart) [27, 28, 30, 34–38]. One study initially met inclusion criteria but was later excluded because it did not report any outcomes separately among Hispanic women [39].

Fig. 1.

PRISMA flow diagram

Study characteristics

Study characteristics are shown in Table 1. A total of 20,123 women were included, 8687 of whom were Hispanic. Study designs included cross-sectional (n = 5), descriptive (n = 2), and nonrandomized observational cohort study (n = 1). Study periods ranged from 1989 to 2020. Five studies examined years before voluntary fortification of corn masa flour [30, 34–36, 38], two included years before and after fortification [27, 28], and one was conducted after voluntary fortification [37]. Four studies utilized data from NHANES across overlapping time periods: 2001–2008, 2007–2012, 2011–2018, and 2011-March 2020 [27, 28, 30, 36]. Despite the overlapping datasets, the studies differed in their populations and the outcomes they focused on, ensuring that each contributed unique findings and minimizing duplication concerns. For instance, Hamner et al. specifically limited their population to MA women rather than the broader Hispanic population of women [36]. Additionally, while both Wang et al. (2021) and Wang et al. (2024) analyzed pre- and post-voluntary fortification cohorts, the latter study included a longer post-voluntary fortification period (2017-March 2020) [27, 28]. Since the pre-voluntary fortification cohort is the same in both studies, the differences in the post-voluntary fortification cohorts provide insight into the early vs. later post-voluntary fortification periods. The risk of bias assessments for each outcome are shown in Supplementary Table 3, Additional File 1. For the outcomes of folic acid fortified foods and acculturation factors, there was a high risk of bias, mostly due to confounding, and mismeasurement of the exposure and the outcome. For the outcomes of folic acid intake, RBC folate concentrations, and NTD rates, there were some concerns for risk of bias due to confounding, selection of participants into the study or into the analysis, and missing data. These studies varied in design, data source, and time periods, which may have contributed to heterogeneity in the reported outcomes.

Table 1.

Study characteristics

Study	Study design	Data source	Years included (pre or post fortification)a	Hispanic (N)	Total (N)	Outcomes reported
Schaffer et al., 1998 [38]	Descriptive	California counties	1989–1991 (pre)	160	462	FA fortified foods, FA intake
Chacko et al., 2003 [35]	Nonrandomized observational cohort	Reproductive health clinics	1999–2000 (pre)	109	387	FA fortified foods
Hamner et al., 2011 [36]	Cross-sectional	NHANES	2001–2008 (pre)	1308	3315	FA fortified foods, FA intake, acculturation factors
Tinker et al., 2015 [30]	Cross-sectional	NHANES	2007–2012 (pre)	1325	3861	FA fortified foods, RBC folate concentrations
Bodnar et al., 2017 [34]	Cross-sectional	Medical centers	2010–2013 (pre)	1374	7511	FA fortified foods
Wang et al., 2021 [28]	Cross-sectional	NHANES	2011–2016 (pre) 2017–2018 (post)	2070	2246	FA fortified foods, FA intake, RBC folate concentrations, NTD rates, acculturation factors
Mirabal-Beltran et al., 2024 [37]	Descriptive	Prenatal clinic	2019 (post)	26	26	FA fortified foods, acculturation factors
Wang et al., 2024 [27]	Cross-sectional	NHANES	2011–2016 (pre) 2017-March 2020 (post)	2315	2315	FA fortified foods, FA intake, RBC folate concentrations, NTD rates, acculturation factors

FA Folic acid, N Number, NHANES National Health and Nutrition Examination Survey, NTD Neural tube defect, RBC Red blood cell

^aPre- or post-voluntary fortification of corn masa flour

Consumption of folic acid fortified foods

The folic acid fortified foods consumed by Hispanic women are shown in Table 2. Four studies compared the consumption of ECGP, RTE, and supplements, and reported that most Hispanic women obtained folic acid from ECGP only [27, 28, 30, 36]. Folic acid intakes from sources were reported in combinations (e.g., ECGP only, ECGP + RTE, ECGP + supplements, and ECGP + RTE + supplements), but the individual contributions of RTE and supplements were not disaggregated in these studies. Bodnar et al. reported that RTE were the highest contributor to folic acid intake followed by bread, rice, and pasta dishes [34]. Schaffer et al. reported that many foreign-born Hispanic women consumed cereal daily (at least seven times per week), with 44.1% reporting daily consumption; the folic acid fortification status of the cereal was not specified [38]. Chacko et al. ranked the primary sources of folic acid in order of popularity from most to least consumed: cereal, flour, pasta products, and burritos [35]. Other commonly cited sources of folic acid included maseca corn flour, rice, and instant oats [37]. Cereal appears to be the most common source of folic acid among Hispanic women, although data on individual contributions of sources are limited and were not consistently reported. The certainty of evidence was downgraded from low to very low due to the high risk of bias, inconsistency of results, and indirectness of evidence, which greatly limits confidence in the findings (Supplementary Table 4, Additional File 1).

Table 2.

Folic acid fortified foods consumed by Hispanic women

Study	Source 1	Source 2	Source 3	Source 4	Source 5
Schaffer et al., 1998 [38]	Cereal
Chacko et al., 2003 [35]	Cereal	Flour	Spaghetti	Macaroni	Burritos
Hamner et al., 2011 [36]	Enriched cereal grain products (ECGP) only	ECGP + RTE	ECGP + SUPP	ECGP + RTE + SUPP
Tinker et al., 2015 [30]	ECGP only	ECGP + RTE	ECGP + SUPP	ECGP + RTE + SUPP
Bodnar et al., 2017 [34]	RTE	Yeast bread	Rice	Pasta dishes
Wang et al., 2021 [28]	ECGP only	ECGP + RTE	ECGP + SUPP	ECGP + RTE + SUPP
Mirabal-Beltran et al., 2024 [37]	Corn flakes cereal	Maseca corn flour	Rice	Quaker instant oats
Wang et al., 2024 [27]	ECGP only	ECGP + RTE	ECGP + SUPP	ECGP + RTE + SUPP

ECGP Enriched cereal grain products, RTE Ready-to-eat cereals, SUPP Supplements

Daily folic acid intake

The daily folic acid intake among Hispanic and NHW women is shown in Table 3. Schaffer et al. reported prior to voluntary folic acid fortification of corn masa flour, Hispanic women had higher daily folic acid intake from dietary sources compared to NHW women (foreign-born Hispanic: 456 mcg, US-born Hispanic: 406 mcg, NHW: 349 mcg, p < 0.001), but no significant difference in daily folic acid intake when supplements were included (foreign-born Hispanic: 484 mcg, US-born Hispanic: 443 mcg, NHW: 501 mcg, p = 0.424) [38]. By contrast, Hamner et al. found no significant difference in daily folic acid intake derived from dietary sources (excluding supplements) between MA women and NHW women pre-voluntary fortification (177 mcg vs. 187 mcg, p > 0.05) [36]. However, when including supplements, MA women consumed significantly less folic acid compared to NHW women (244 mcg vs. 332 mcg, p < 0.05) and were more likely to report a total daily folic acid intake < 400 mcg (86.7% vs. 70.1%, p < 0.05) [36]. Wang and colleagues reported no significant difference in daily folic acid intake among Hispanic women pre- and post-voluntary fortification, with intake levels remaining low (223 mcg vs. 197 mcg, p = 0.84) [27, 28]. Similarly, there was no difference in the percentage of Hispanic women with total daily intake < 400 mcg (86.1% pre-voluntary fortification vs. 87.8% post-voluntary fortification, p = 0.38) [27]. Both studies analyzed overlapping NHANES datasets but differed in their populations, with the latter including a more recent cohort from 2017-March 2020 [27, 28]. Despite this, both reported no significant differences in folic acid intake pre- and post-voluntary fortification. Although initial differences in folic acid intake by dietary sources and supplements were observed pre-voluntary fortification, the voluntary fortification of corn masa flour did not result in a significant increase in folic acid intake among Hispanic women or a reduction in the proportion with inadequate intake. There were no serious factors that warranted downgrading or upgrading the certainty of evidence, therefore certainty remained low, and the true effect may be different from the findings (Supplementary Table 4, Additional File 1).

Table 3.

Daily folic acid intake among Hispanic and NHW women

Study	Time period	Daily folic acid intakea, mcg (95% CI or IQR)		N
		Hispanic	NHW	Hispanic	NHW
Schaffer et al., 1998b [38]	Pre-voluntary fortification	US-born: 443 ± 240 Foreign-born: 484 ± 272	501 ± 349	US-born: 63 Foreign born: 90	243
Hamner et al., 2011c [36]	Pre-voluntary fortification	244 (205, 282)*	332 (298, 366)	1308	2007
Wang et al., 2021d [28]	Pre-voluntary fortification	177 (85, 299)	231 (118, 392)	1643	1736
	Post-voluntary fortification	161 (71, 277)	182 (78, 351)	427	510
Wang et al., 2024d [27]	Pre-voluntary fortification	223 (140, 275)	-	1602	-
	Post-voluntary fortification	197 (132, 275)	-	672	-
Study	Time period	Total daily intake < 400 mcga, % (95% CI)		N
		Hispanic	NHW	Hispanic	NHW
Hamner et al., 2011c [36]	Pre-voluntary fortification	86.7 (81.1, 92.3)*	70.1 (66.2, 74.1)	1308	2007
Wang et al., 2024 [27]	Pre-voluntary fortification	86.1 (83.7, 88.5)	-	1406	-
	Post-voluntary fortification	87.8 (84.8, 90.7)	-	594	-

CI Confidence interval, IQR Interquartile range, mcg Micrograms, N Number, NHW Non-Hispanic White, US United States

^aIncludes consumption of supplements

^bReport intake with standard deviation

^cIntake among Mexican American women; report intake with 95% CI

^dReport intake with IQR

^*Statistically significant difference between Mexican American and NHW women, p < 0.05

RBC folate concentrations and NTD rates

Three studies examined RBC folate concentrations among Hispanic and NHW women, regardless of folic acid source, with two studies also estimating NTD rates [27, 28, 30]. Tinker et al. reported significantly lower RBC folate concentrations among Hispanic women (963 nmol/L, 95% confidence interval (CI) 934–982) compared with NHW women (1043 nmol/L; 95% CI, 1022–1075) [30]. Following voluntary fortification of corn masa flour, the odds of having suboptimal RBC folate concentrations among Hispanic women compared with NHW women remained elevated (odds ratio 1.05, 95% CI 0.83–1.33 pre-fortification; odds ratio 1.15, 95% CI 0.45–2.94 post-fortification); however, this was not statistically significant [28]. There was no significant difference in the percentage of Hispanic women with suboptimal RBC folate concentrations before and after voluntary fortification (16.8% vs. 19.4%, p = 0.20) [27]. These findings suggest that RBC folate concentrations among Hispanic women remain lower than those of NHW women, with no improvements following voluntary fortification. The certainty of evidence remained low due to the absence of serious limitations but confidence in the findings is limited (Supplementary Table 4, Additional File 1).

In the two years after voluntary fortification, Wang et al. (2021) estimated the NTD rate to be 7.5/10,000 live births among Hispanic women who obtained folic acid from ECGP and corn masa flour only, which was not significantly different from the estimated NTD rate among NHW women (7.1/10,000 live births, p = 0.37) [28]. Using a dataset that spanned several years before and after voluntary fortification (2011-March 2020), Wang et al. (2024) reported an estimated NTD rate of 6.8/10,000 live births among all Hispanic women and 7.5/10,000 live births among Hispanic women who obtained folic acid from ECGP and corn masa flour [27]. These findings indicate the estimated NTD rate among Hispanic women remains comparable to those of NHW women, but there is no evidence supporting a reduction of the rate among Hispanic women post-voluntary fortification. The certainty of evidence remained low, which limits confidence in the findings (Supplementary Table 4, Additional File 1).

Acculturation factors

The daily folic acid intake among Hispanic women stratified by acculturation factors is shown in Table 4. Hamner et al. did not find statistically significant differences in folic acid intake derived from ECGP and ECGP + RTE among Hispanic women by acculturation factors; however, when including supplements, Hispanic women who reported speaking Spanish all or most of the time (224 mcg) or reported speaking Spanish and English equally at home (206 mcg) had lower daily folic acid intake compared with NHW women (332 mcg, p < 0.05) [36]. In addition to acculturation, Hamner et al. also examined interactions between acculturation and sociodemographic factors (education level and poverty income ratio), and found that among Hispanic women with at least a high school education, those who had been in the US < 15 years were at greater risk of having insufficient folic acid intake compared to those who had been in the US for ≥ 15 years. Following voluntary fortification, Wang et al. (2021) reported no differences in daily folic acid intake among Hispanic women by acculturation factors [28]. By contrast, Wang et al. (2024) reported a statistically significant increase in daily folic acid intake among Hispanic women who spoke primarily Spanish at home (150 mcg pre-voluntary fortification vs. 152 mcg post-voluntary fortification, p < 0.01) [27]. Among Hispanic women who consumed ECGP only, Wang et al. (2024) also noted significant increases in RBC folate concentrations following voluntary fortification in women who spoke primarily Spanish at home (933 nmol/L pre-voluntary fortification vs. 1018 nmol/L post-voluntary fortification, p = 0.01) and those born outside the US residing in the US < 15 years (872 nmol/L pre-voluntary fortification vs. 961 nmol/L post-voluntary fortification, p = 0.01) [27]. Mirabal-Beltran et al. reported that women residing in the US for ≤ 5 years had diets reflective of their native countries, while those residing in the US for > 5 years reported more typical American diets [37]; this study did not examine the impact of acculturation on folic acid intake specifically. Overall, these findings suggest limited differences in folic acid intake by acculturation factors, with some evidence of increased intake and RBC folate concentrations among less accultured groups following fortification. The certainty of evidence was downgraded from low to very low due to the high risk of bias and inconsistency of results, which greatly limits confidence in these results (Supplementary Table 4, Additional File 1).

Table 4.

Daily folic acid intake stratified by acculturation factors among Hispanic women

Study	Time period	Daily folic acid intakea, mcg (95% CI or IQR)
		Language spoken at home			Time in the US
		Primarily Spanish	Equal Spanish & English	Primarily English	US-born	< 15 years in the US	≥ 15 years in the US
Hamner et al., 2011b [36]	Pre-voluntary fortification ECGP	149 (98, 199)	139 (116, 163)	150 (121, 178)	146 (116, 176)	150 (115, 186)	146 (107, 186)
	Pre-voluntary fortification ECGP + RTE	175 (140, 210)	163 (137, 189)	182 (160, 205)	177 (160, 194)	175 (149, 203)	177 (159, 196)
Wang et al., 2021c [28]	Pre-voluntary fortification	100 (68, 132)	97 (60, 143)	121 (91, 154)	115 (87, 146)	102 (70, 133)	99 (55, 149)
	Post-voluntary fortification	114 (31, 172)	107 (64, 148)	121 (83, 162)	122 (78, 169)	114 (39, 165)	126 (98, 150)
Wang et al., 2024c [27]	Pre-voluntary fortification	150 (113, 193)	146 (111, 188)	147 (111, 189)	147 (111, 189)	149 (113, 192)	152 (116, 196)
	Post-voluntary fortification	152 (115, 195)*	145 (110, 187)	145 (110, 188)	145 (109, 187)	150 (114, 193)	152 (116, 195)

CI Confidence interval, ECGP Enriched cereal grain products, IQR Interquartile range, mcg Micrograms, RTE Ready-to-eat cereals, US United States

^aExcludes consumption of supplements

^bIntake from ECGP and ECGP + RTE among Mexican American women; report intake with 95% CI

^cIntake from ECGP only; report intake with IQR

^*Statistically significant difference between pre- and post-voluntary fortification, p < 0.01

Discussion

Hispanic women have lower dietary folic acid intake compared to NHW women and there remains a greater prevalence of NTD among Hispanic births in the US [13]. Intake of folic acid can be increased through two avenues: (1) consumption through a standard diet of folic acid fortified foods and (2) education about and access to folic acid supplements [40]. Our findings suggest that Hispanic women rely more on dietary folic acid than supplements [36, 38]. Culture and socioeconomic status may influence dietary choices, potentially limiting Hispanic women from consuming recommended amounts through diet alone [18]. While no significant differences in dietary folic acid intake were found across acculturation factors, low acculturation factors, such as speaking predominately Spanish and recent immigration, contributed to reduced total folic acid intake among Hispanic women in one study [36]. To the best of our knowledge, no evidence synthesis on folic acid intake or status among Hispanic women in the US has been published.

Cereals constitute a major source of folic acid for Hispanic women surpassing other foods such as pasta, flour, bread, and rice. Corn masa flour was also cited as a commonly consumed ingredient, however there was a discrepancy when attributing the contribution to total folic acid intake. Corn masa flour is a cultural staple in many Hispanic diets, making it an appealing source to fortify without necessitating significant alterations in dietary practices. An approximate 21% increase was predicted in daily folic acid intake after the fortification of corn masa flour in MA women of reproductive age; however, no substantial increase in folic acid intake has been reported thus far [27, 28, 36]. Furthermore, research has yet to demonstrate a significant decrease in NTD rates among Hispanic women of reproductive age following fortification [23]. It is theorized this shortcoming is due to the fortification of only 7–10% of corn masa flour products, a consequence likely attributed to the voluntary, rather than mandatory, fortification of these products [2, 41]. Additionally, this could be impacted by lead-time bias. Costa Rica and Brazil have seen a reduction in NTD rates after the enactment of mandatory corn masa fortification, with Costa Rica reporting a 51% reduction, one of the highest, likely due to wider fortification of products including wheat flour, maize flour, milk, and rice [42, 43]. Costa Rica enforces mandatory food fortification through coordinated monitoring of its national program, collaborative efforts with research institutions like the Instituto Costarricense de Investigación y Enseñanza en Nutrición y Salud, and clear standards for enforcement, including penalties for non-compliance with fortification levels [44]. In the US, manufacturers that voluntarily fortify their products are expected to follow FDA guidelines, and the agency may take enforcement action if non-compliance is identified [45]. Applying strategies similar to Costa Rica, such as establishing collaborative monitoring programs and clearer standards for voluntary fortification, could address current gaps in voluntary fortification efforts in the US.

Although mandatory fortification of enriched grains with folic acid has been effective overall in the US, many Hispanic women may face barriers to accessing fortified grains. Hispanic individuals are twice as likely to experience food insecurity compared to NHW individuals [46]. Access to grocery stores is limited in areas with a large Hispanic population, reducing the availability of healthy food options such as fresh produce and less processed foods [47, 48]. Given that healthier food options are often less available in food-insecure areas, similar barriers may exist for fortified grains as well, which may impact folic acid intake and reduce the effectiveness of fortification efforts among Hispanic women. While this review focused on acculturation factors and their association with folic acid, broader social and structural risk factors may also influence intake patterns. Among the studies included, only one examined education level and poverty income ratio, and found no consistent significant interactions—aside from a single association between education level and length of time residing in the US [36]. Due to the limited available data, these risk factors could not be synthesized. Prior studies have identified cost as a barrier to supplement use for Hispanic women [49, 50]; however, further research is needed to explore how these factors impact folic acid intake.

Recognizing the heterogeneity of the Hispanic population in the US is also critical, as Hispanic individuals have geographic origins in many different countries—each with its own culture and dietary preference. Treating the Hispanic population as a single group overlooks the potential influence that geographic origin has on the consumption of folic acid [51–53]. One suggested solution with increased reach is the fortification of salt, an affordable and widely used ingredient. Salt has been a safe and effective vehicle to increase iodine intake globally [54]. Extending this approach to include folic acid in salt is supported by studies that have shown its cost-effectiveness and potential to prevent NTD [55, 56]. In a recent nonrandomized controlled trial, folic acid fortified salt was associated with increased serum folate concentrations in women [57]. As a culturally universal ingredient, the fortification of salt presents a promising strategy to increase folic acid intake in all populations, and interventions targeting Hispanics can be created to address disparities.

Beyond barriers to fortified foods, barriers to healthcare access may impact folic acid intake among Hispanic women. Barriers such as cost, health insurance, transportation, employment or school obligations, and limited support from family or friends often limit Hispanic women’s access to healthcare, especially prenatal care [58–60]. Even after overcoming significant barriers to access care, Hispanic women often face difficulty in communicating with their healthcare providers during their appointments. The lack of linguistic and cultural competencies among providers are two main barriers to effective communication cited by Hispanic women [61, 62]. Without access to timely and adequate care, women are unable to receive the education and guidance needed to support their health before and after conception. While most Hispanic women acknowledge hearing some information about taking folic acid, whether from a doctor, friend, or online source, many do not know when to take it, the correct dosage, or its significance [63]. Mirabal-Beltran et al. reported that 30% of women in their study were prescribed or recommended prenatal vitamins but reported a lack of education regarding their use [37]. This knowledge gap is concerning because physicians are often the primary source of health education for these women [63].

Public health initiatives aimed at addressing barriers in access to prenatal care and targeted educational efforts among Hispanic women are essential to ensure that women receive the necessary information and support to reduce their risk of NTD. A 2013 study developed advertisements highlighting the broad benefits of multivitamin use, targeting Hispanic adolescents and mothers, and demonstrated improvements in awareness of and intention to take multivitamins [64]. Another targeted educational effort involves the Promotora de Salud model, which leverages interpersonal connections by engaging individuals who share the same culture and language as the target population [65]. Recent findings indicate this approach has successfully increased general awareness about folic acid and led to improved supplement consumption following program implementation [15].

Although the importance of adequate folic acid intake is well-established within the scientific community, targeted design of interventions for the Hispanic population could benefit from better understanding dietary patterns, supplement use, and the availability of fortified foods. Appropriately tailored public health campaigns, such as the Promotora de Salud model, could then bridge the gap between research and public awareness on the importance of adequate folic acid intake. The United Nations Children’s Fund and the Global Alliance for the Prevention of Spina Bifida, among other organizations, support research evaluating the effectiveness of current strategies and lay the foundation for implementing large-scale fortification programs. Former campaigns from these and similar organizations have demonstrated effectiveness in disease reduction globally, underscoring the benefit of culturally appropriate initiatives targeting NTD [66, 67]. Targeted education endeavors can be paired with advocacy and public health efforts to comprehensively address the increased NTD burden in Hispanic women.

This review has several important limitations. Only three databases were included, therefore the search may not have captured all possible data sources. Additionally, the search was limited to published studies, potentially missing data from ongoing research and studies published after September 9, 2024. The review could be most influenced by publication, lead-time, sample, and reporting bias. Many of the data sources were survey-based. The use of survey methods, particularly in retrospective studies aiming to assess nutritional intake before and during pregnancy, can introduce recall bias, especially when conducted after delivery. The NHANES database employs a different methodology, utilizing 24-h food diaries, which may help mitigate recall bias. However, four studies relied on this data, potentially introducing duplication bias that could not be controlled. To minimize the effect of duplication bias, we were unable to complete formal synthesis of data reported. The heterogeneity of study designs and variable measures also limited the comparability and generalizability of results across studies. Increased standardization of reporting and methods in future studies are required to enable more robust synthesis and deepen our understanding in this population. Furthermore, many of the studies recruited patients exclusively from prenatal care clinics, thereby limiting our understanding of consumption patterns in individuals without access to prenatal care—which may represent the group at highest risk.

The small number of studies and lack of standardized reporting on sources of folic acid underscores a significant gap in our understanding of the dietary patterns and the associated risk factors that may contribute to suboptimal intake levels among Hispanic women. Nevertheless, we find that there remains an increased NTD burden and a lack of insight into why. The scarcity of publications on the consumption of folic acid among Hispanic women is a significant finding that should encourage further research into this topic.

Conclusions

There is lower folic acid intake and increased NTD burden in Hispanic women compared with NHW women in the US. The literature lacks comprehensive insights into the consumption patterns of folic acid fortified foods among Hispanic women; this is the first step in understanding why Hispanic women continue to have increased NTD burden. A multi-pronged approach involving research efforts, education, prenatal care, and policy is required to successfully address the ongoing disparity that continues to be prevalent despite current fortification endeavors.

Abbreviations

CI

Confidence interval

ECGP

Enriched cereal grain products

FDA

Food and Drug Administration

GRADE

Grading of Recommendations, Assessment, Development, and Evaluations

IQR

Interquartile range

Mcg

Micrograms

MA

Mexican American

NHANES

National Health and Nutrition Examination Survey

NHW

Non-Hispanic White

NTD

Neural tube defect

PRISMA

Preferred Reviews and Meta-Analyses

RBC

Red blood cell

ROBINS-E

Risk of Bias in Non-randomized Studies-of Exposure

RTE

Ready-to-eat cereals

US

United States

Vs.

Versus

Authors’ contributions

N.V. and S.A. completed the acquisition, analysis, and interpretation of data. N.V. and K.B. drafted and revised the manuscript. S.A. and M.V. substantially revised the manuscript. S.K.L. and R.M.G. provided supervision on manuscript design, methods, and critical review. All authors read and approved the final manuscript.

Funding

The authors received no funding for this study.

Data availability

Data generated or analyzed during this study are provided within the manuscript or supplementary information file.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.