Maternal and Cord Blood Folate Concentrations Are Inversely Associated with Fetal DNA Hydroxymethylation, but Not DNA Methylation, in a Cohort of Pregnant Canadian Women

Uncovering the Hidden Dangers and Molecular Mechanisms of Excess Folate: A Narrative Review

This review delves into the intricate relationship between excess folate (vitamin B9) intake, especially its synthetic form, namely, folic acid, and its implications on health and disease. While folate plays a pivotal role in the one-carbon cycle, which is essential for DNA synthesis, repair, and methylation, concerns arise about its excessive intake. The literature underscores potential deleterious effects, such as an increased risk of carcinogenesis; disruption in DNA methylation; and impacts on embryogenesis, pregnancy outcomes, neurodevelopment, and disease risk. Notably, these consequences stretch beyond the immediate effects, potentially influencing future generations through epigenetic reprogramming. The molecular mechanisms underlying these effects were examined, including altered one-carbon metabolism, the accumulation of unmetabolized folic acid, vitamin-B12-dependent mechanisms, altered methylation patterns, and interactions with critical receptors and signaling pathways. Furthermore, differences in the effects and mechanisms mediated by folic acid compared with natural folate are highlighted. Given the widespread folic acid supplementation, it is imperative to further research its optimal intake levels and the molecular pathways impacted by its excessive intake, ensuring the health and well-being of the global population.

High Dietary Folic Acid Intake Is Associated with Genomic Instability in Peripheral Lymphocytes of Healthy Adults

Mandatory fortification of food with synthetic folic acid (FA) was instituted in 1998 to reduce the incidence of neural tube defects. Adequate folate status is correlated with numerous health benefits. However, elevated consumption of FA is controversially associated with deleterious effects on health. We previously reported that excess FA mimicked folate depletion in a lymphoblastoid cell line. To explore the impact of FA intake from fortified food, we conducted an observational human study on 33 healthy participants aged 18-40 not taking any supplements. Food intake, anthropomorphic measurements, and blood samples were collected and analyzed. Our results show that individuals belonging to the highest tertile of folic acid intake, as well as ones with the highest folic acid to total folate intake ratio (FAR), display a significantly greater incidence of lymphocyte genomic damage. A decrease in global DNA methylation is observed in the highest tertile of FAR compared to the lowest (p = 0.055). A downward trend in the overall gene expression of select DNA repair and one carbon cycle genes (MGMT, MLH1, UNG, MTHFR, MTR) is noted with increased folate status and FA intake. These results provide supporting evidence that high consumption of FA from fortified foods can precipitate genomic instability in peripheral lymphocyte in vivo.

Prenatal vitamin intake in first month of pregnancy and DNA methylation in cord blood and placenta in two prospective cohorts

BACKGROUND

Prenatal vitamin use is recommended before and during pregnancies for normal fetal development. Prenatal vitamins do not have a standard formulation, but many contain calcium, folic acid, iodine, iron, omega-3 fatty acids, zinc, and vitamins A, B6, B12, and D, and usually they contain higher concentrations of folic acid and iron than regular multivitamins in the US Nutrient levels can impact epigenetic factors such as DNA methylation, but relationships between maternal prenatal vitamin use and DNA methylation have been relatively understudied. We examined use of prenatal vitamins in the first month of pregnancy in relation to cord blood and placenta DNA methylation in two prospective pregnancy cohorts: the Early Autism Risk Longitudinal Investigation (EARLI) and Markers of Autism Risk Learning Early Signs (MARBLES) studies.

RESULTS

In placenta, prenatal vitamin intake was marginally associated with -0.52% (95% CI -1.04, 0.01) lower mean array-wide DNA methylation in EARLI, and associated with -0.60% (-1.08, -0.13) lower mean array-wide DNA methylation in MARBLES. There was little consistency in the associations between prenatal vitamin intake and single DNA methylation site effect estimates across cohorts and tissues, with only a few overlapping sites with correlated effect estimates. However, the single DNA methylation sites with p-value < 0.01 (EARLI cord nCpGs = 4068, EARLI placenta nCpGs = 3647, MARBLES cord nCpGs = 4068, MARBLES placenta nCpGs = 9563) were consistently enriched in neuronal developmental pathways.

CONCLUSIONS

Together, our findings suggest that prenatal vitamin intake in the first month of pregnancy may be related to lower placental global DNA methylation and related to DNA methylation in brain-related pathways in both placenta and cord blood.

Red cell folate status among a subset of Canadian children with Down Syndrome post-fortification

BACKGROUND

Trisomy 21 or Down Syndrome (DS) is associated with altered methylation pathways. Children with DS may therefore represent a population subgroup with vulnerability to increased exposures to folic acid, which is involved in one-carbon metabolism. Folic acid (FA) fortification of flour and maternal FA supplementation are intended to reduce neural tube defects related to folate deficiency. The interventions have been widely successful in Canada. Emerging evidence suggests that higher FA exposures may also have potential negative consequences, including implications for DNA methylation. This retrospective chart review provides insight on the red blood cell (RBC) folate status of a subset of Canadian children and infants with DS, post-fortification.

METHODS

Children with DS in two Canadian provinces were assessed in the community. Access to RBC folate testing was variable, limiting sample size to 39 (n = 27 for children ≤6 years; n = 12 for children 6-18 years). All children with DS and an RBC folate result were included. The use of FA-containing supplements and formula was documented.

RESULTS

Among children 6-18 years, 100% had RBC folates >1000 nmol/L, 50% were >2000 nmol/L and 25% had levels above the upper laboratory reporting limit. Among the younger children (<6 years), 52% had RBC folates >2000 nmol and 2 children exceeded 3000 nmol/L. Among exclusively breast-fed infants (<12 months), 100% had RBC folates >1000 nmol/L and 50% had levels >2000 nmol/L, suggestive of in-utero or maternal exposures. RBC folate status among this subset of Canadian children with DS is higher than documented for the larger Canadian population, and higher than among US children with DS.

CONCLUSIONS

Young Canadian children with DS demonstrated high post-fortification RBC folate status. RBC folate status was higher than reported for the larger Canadian population, and higher than for US children with Down Syndrome. Consumption of folic acid-containing formula and/or supplements was relatively low among these Canadian children with DS, suggesting maternal FA supplements and/or FA-fortified foods may be important etiological factors. A larger, prospective study is needed to validate these results, and to explore potential health implications among this vulnerable population.

Knowledge gaps in understanding the metabolic and clinical effects of excess folates/folic acid: a summary, and perspectives, from an NIH workshop

Folate, an essential nutrient found naturally in foods in a reduced form, is present in dietary supplements and fortified foods in an oxidized synthetic form (folic acid). There is widespread agreement that maintaining adequate folate status is critical to prevent diseases due to folate inadequacy (e.g., anemia, birth defects, and cancer). However, there are concerns of potential adverse effects of excess folic acid intake and/or elevated folate status, with the original concern focused on exacerbation of clinical effects of vitamin B-12 deficiency and its role in neurocognitive health. More recently, animal and observational studies have suggested potential adverse effects on cancer risk, birth outcomes, and other diseases. Observations indicating adverse effects from excess folic acid intake, elevated folate status, and unmetabolized folic acid (UMFA) remain inconclusive; the data do not provide the evidence needed to affect public health recommendations. Moreover, strong biological and mechanistic premises connecting elevated folic acid intake, UMFA, and/or high folate status to adverse health outcomes are lacking. However, the body of evidence on potential adverse health outcomes indicates the need for comprehensive research to clarify these issues and bridge knowledge gaps. Three key research questions encompass the additional research needed to establish whether high folic acid or total folate intake contributes to disease risk. 1) Does UMFA affect biological pathways leading to adverse health effects? 2) Does elevated folate status resulting from any form of folate intake affect vitamin B-12 function and its roles in sustaining health? 3) Does elevated folate intake, regardless of form, affect biological pathways leading to adverse health effects other than those linked to vitamin B-12 function? This article summarizes the proceedings of an August 2019 NIH expert workshop focused on addressing these research areas.

Nutrients, Mitochondrial Function, and Perinatal Health

Mitochondria are active independent organelles that not only meet the cellular energy requirement but also regulate central cellular activities. Mitochondria can play a critical role in physiological adaptations during pregnancy. Differences in mitochondrial function have been found between healthy and complicated pregnancies. Pregnancy signifies increased nutritional requirements to support fetal growth and the metabolism of maternal and fetal tissues. Nutrient availability regulates mitochondrial metabolism, where excessive macronutrient supply could lead to oxidative stress and contribute to mitochondrial dysfunction, while micronutrients are essential elements for optimal mitochondrial processes, as cofactors in energy metabolism and/or as antioxidants. Inadequate macronutrient and micronutrient consumption can result in adverse pregnancy outcomes, possibly through mitochondrial dysfunction, by impairing energy supply, one-carbon metabolism, biosynthetic pathways, and the availability of metabolic co-factors which modulate the epigenetic processes capable of establishing significant short- and long-term effects on infant health. Here, we review the importance of macronutrients and micronutrients on mitochondrial function and its influence on maternal and infant health.