Lynn B. Bailey

Folate and DNA Methylation: A Review of Molecular Mechanisms and the Evidence for Folate’s Role

DNA methylation is an epigenetic modification critical to normal genome regulation and development. The vitamin folate is a key source of the one carbon group used to methylate DNA. Because normal mammalian development is dependent on DNA methylation, there is enormous interest in assessing the potential for changes in folate intake to modulate DNA methylation both as a biomarker for folate status and as a mechanistic link to developmental disorders and chronic diseases including cancer. This review highlights the role of DNA methylation in normal genome function, how it can be altered, and the evidence of the role of folate/folic acid in these processes.

Folic acid food fortification-its history, effect, concerns, and future directions.

Periconceptional intake of folic acid is known to reduce a womans risk of having an infant affected by a neural tube birth defect (NTD). National programs to mandate fortification of food with folic acid have reduced the prevalence of NTDs worldwide. Uncertainty surrounding possible unintended consequences has led to concerns about higher folic acid intake and food fortification programs. This uncertainty emphasizes the need to continually monitor fortification programs for accurate measures of their effect and the ability to address concerns as they arise. This review highlights the history, effect, concerns, and future directions of folic acid food fortification programs.

Biomarkers of Nutrition for Development—Folate Review

The Biomarkers of Nutrition for Development (BOND) project is designed to provide evidence-based advice to anyone with an interest in the role of nutrition in health. Specifically, the BOND program provides state-of-the-art information and service with regard to selection, use, and interpretation of biomarkers of nutrient exposure, status, function, and effect. To accomplish this objective, expert panels are recruited to evaluate the literature and to draft comprehensive reports on the current state of the art with regard to specific nutrient biology and available biomarkers for assessing nutrients in body tissues at the individual and population level. Phase I of the BOND project includes the evaluation of biomarkers for 6 nutrients: iodine, iron, zinc, folate, vitamin A, and vitamin B-12. This review represents the second in the series of reviews and covers all relevant aspects of folate biology and biomarkers. The article is organized to provide the reader with a full appreciation of folates history as a public health issue, its biology, and an overview of available biomarkers (serum folate, RBC folate, and plasma homocysteine concentrations) and their interpretation across a range of clinical and population-based uses. The article also includes a list of priority research needs for advancing the area of folate biomarkers related to nutritional health status and development.

Folic acid source, usual intake, and folate and vitamin B-12 status in US adults: National Health and Nutrition Examination Survey (NHANES) 2003–2006

BACKGROUND US adults have access to multiple sources of folic acid. The contribution of these sources to usual intakes above the tolerable upper intake level (UL) (1000 microg/d) and to folate and vitamin B-12 status is unknown. OBJECTIVE The objective was to estimate usual folic acid intake above the UL and adjusted serum and red blood cell folate, vitamin B-12, methylmalonic acid, and homocysteine concentrations among US adults by 3 major folic acid intake sources-enriched cereal-grain products (ECGP), ready-to-eat cereals (RTE), and supplements (SUP)-categorized into 4 mutually exclusive consumption groups. DESIGN We used data from the National Health and Nutrition Examination Survey (NHANES) 2003-2006 (n = 8258). RESULTS Overall, 2.7% (95% CI: 1.9%, 3.5%) of adults consumed more than the UL of folic acid. The proportions of those who consumed folic acid from ECGP only, ECGP+RTE, ECGP+SUP, and ECGP+RTE+SUP were 42%, 18%, 25%, and 15%, respectively. Of 60% of adults who did not consume supplements containing folic acid (ECGP only and ECGP+RTE), 0% had intakes that exceeded the UL. Of 34% and 6% of adults who consumed supplements with an average of < or = 400 and >400 microg folic acid/d, <1% and 47.8% (95% CI: 39.6%, 56.0%), respectively, had intakes that exceeded the UL. Consumption of RTE and/or supplements with folic acid was associated with higher folate and vitamin B-12 and lower homocysteine concentrations, and consumption of supplements with vitamin B-12 was associated with lower methylmalonic acid concentrations (P < 0.001). CONCLUSION At current fortification levels, US adults who do not consume supplements or who consume an average of < or =400 microg folic acid/d from supplements are unlikely to exceed the UL in intake for folic acid.

Fortification of flour with folic acid

Background After randomized, controlled trials established that consumption of folic acid before pregnancy and during the early weeks of gestation reduces the risk of a neural tube defect (NTD)-affected pregnancy, the United States Public Health Service recommended in 1992 that all women capable of becoming pregnant consume 400 μg folic acid daily. In 1998, folic acid fortification of all enriched cereal grain product flour was fully implemented in the United States and Canada. Objective To provide guidance on national fortification of wheat and maize flours to prevent 50 to 70% of the estimated 300,000 NTD-affected pregnancies worldwide. Methods An expert workgroup reviewed the latest evidence of effectiveness of folic acid flour fortification and the safety of folic acid. Results Recent estimates show that in the United States and Canada, the additional intake of about 100 to 150 μg/day of folic acid through food fortification has been effective in reducing the prevalence of NTDs at birth and increasing blood folate concentrations in both countries. Most potential adverse effects associated with folic acid are associated with extra supplement use not mandatory fortification. Fortification of wheat flour has a proven record of prevention in other developed countries. In 2009, 51 countries had regulations written for mandatory wheat flour fortification programs that included folic acid. Conclusions NTDs remain an important cause of perinatal mortality and infantile paralysis worldwide. Mandatory fortification of flour with folic acid has proved to be one of the most successful public health interventions in reducing the prevalence of NTD-affected pregnancies. Most developing countries have few, if any, common sources of folic acid, unlike many developed countries, which have folic acid available from ready-to-eat cereals and supplements. Expanding the number of developed and developing countries with folic acid flour fortification has tremendous potential to safely eliminate most folic acid-preventable NTDs.

Folic acid and L-5-methyltetrahydrofolate: comparison of clinical pharmacokinetics and pharmacodynamics.

There is a large body of evidence to suggest that improving periconceptional folate status reduces the risk of neonatal neural tube defects. Thus increased folate intake is now recommended before and during the early stages of pregnancy, through folic acid supplements or fortified foods. Furthermore, there is growing evidence that folic acid may have a role in the prevention of other diseases, including dementia and certain types of cancer.Folic acid is a synthetic form of the vitamin, which is only found in fortified foods, supplements and pharmaceuticals. It lacks coenzyme activity and must be reduced to the metabolically active tetrahydrofolate form within the cell. L-5-methyl-tetrahydrofolate (L-5-methyl-THF) is the predominant form of dietary folate and the only species normally found in the circulation, and hence it is the folate that is normally transported into peripheral tissues to be used for cellular metabolism. L-5-methyl-THF is also available commercially as a crystalline form of the calcium salt (Metafolin®), which has the stability required for use as a supplement.Studies comparing L-5-methyl-THF and folic acid have found that the two compounds have comparable physiological activity, bioavailability and absorption at equimolar doses. Bioavailability studies have provided strong evidence that L-5-methyl-THF is at least as effective as folic acid in improving folate status, as measured by blood concentrations of folate and by functional indicators of folate status, such as plasma homocysteine.Intake of L-5-methyl-THF may have advantages over intake of folic acid. First, the potential for masking the haematological symptoms of vitamin B12 deficiency may be reduced with L-5-methyl-THF. Second, L-5-methyl-THF may be associated with a reduced interaction with drugs that inhibit dihydrofolate reductase.

MTHFR 677C→T genotype is associated with folate and homocysteine concentrations in a large, population-based, double-blind trial of folic acid supplementation

BACKGROUND The methylenetetrahydrofolate reductase (MTHFR) genotype is associated with modification of disease and risk of neural tube defects. Plasma and red blood cell (RBC) folate and plasma homocysteine concentrations change in response to daily intakes of folic acid supplements, but no large-scale or population-based randomized trials have examined whether the MTHFR genotype modifies the observed response. OBJECTIVE We sought to determine whether the MTHFR 677C→T genotype modifies the response to folic acid supplementation during and 3 mo after discontinuation of supplementation. DESIGN Northern Chinese women of childbearing age were enrolled in a 6-mo supplementation trial of different folic acid doses: 100, 400, and 4000 μg/d and 4000 μg/wk. Plasma and RBC folate and plasma homocysteine concentrations were measured at baseline; after 1, 3, and 6 mo of supplementation; and 3 mo after discontinuation of supplementation. MTHFR genotyping was performed to identify a C→T mutation at position 677 (n = 932). RESULTS Plasma and RBC folate and homocysteine concentrations were associated with MTHFR genotype throughout the supplementation trial, regardless of folic acid dose. MTHFR TT was associated with lower folate concentrations, and the trend of TT < CC was maintained at even the highest doses. Folic acid doses of 100 μg/d or 4000 μg/wk did not reduce high homocysteine concentrations in those with the MTHFR TT genotype. CONCLUSION MTHFR genotype was an independent predictor of plasma and RBC folate and plasma homocysteine concentrations and did not have a significant interaction with folic acid dose during supplementation. This trial was registered at clinicaltrials.gov as NCT00207558.

Total Parenteral Nutrition in the Mouse: Development of a Technique

A method for total parenteral nutrition in the mouse was developed using commercially available supplies and equipment. The mouses inferior vena cava was catheterized and the catheter was exteriorized from the tail. Mice (average body weight 22.5 g) were not tethered but instead were partially restrained by immobilizing the tail to protect the infusion tubing. A solution was formulated to contain 40% dextrose and 4.3% amino acids plus vitamins, electrolytes, and trace elements. It was administered via pump in graded fashion for the first 3 days to allow the mice to adapt, and then at a rate of 8 ml/day thereafter. This volume provided approximately 12 kcal and 54 mg nitrogen per day and was calculated to meet the needs of the mouse fed per os according to guidelines of the National Research Council. During the adaptation period mice lost weight but they were in positive N balance thereafter. At the end of 12 days body weight was not different than at the start, indicating the adequacy of nutrient input. Further, there were no differences in nitrogen balance or body weight in total parenteral nutrition fed mice in comparison with tail-restrained mice given the same solution per os. All mice appeared to tolerate the partial restraint without incidence and showed no untoward side effects. The rationale and validity of this technique is discussed in detail.

New standard for dietary folate intake in pregnant women

The Institute of Medicine Panel for Folate and Other B Vitamins and Choline considered data from population-based and metabolic studies to revise the dietary intake standards for pregnancy. The recommended dietary allowance (RDA) for pregnant women is the average daily dietary intake sufficient to meet the requirements of 97-98% of pregnant women. The RDA is derived from the amount estimated to meet the requirement of half of healthy pregnant women, or the estimated average requirement (EAR). Maintenance of red cell folate was selected as the primary indicator of adequacy of folate status during pregnancy. The dietary folate equivalent (DFE) was used to interpret studies in which folate was provided as a combination of food folate and synthetic folic acid because folic acid is more bioavailable than is food folate. Many population-based studies confirmed that approximately 680 nmol (approximately 300 microg) folic acid/d consumed in conjunction with a low-folate diet prevented folate deficiency in pregnant women. Additional studies showed that 227 nmol (100 microg) folic acid/d was inadequate to maintain normal folate status in a significant percentage of the groups assessed. The EAR was derived by adding the DFE of this quantity [454 nmol (200 microg)/d] to the EAR for nonpregnant women [725 nmol (320 microg)/d] to provide an EAR of 1178 nmol (520 microg)/d. The RDA of 1362 nmol (600 microg) DFE/d was derived by multiplying the EAR by 1.2 to account for an estimated 10% CV. Data from the metabolic studies support an RDA of 1362 nmol (600 microg) DFE/d on the basis of the maintenance of normal red cell folate concentrations and agree with the findings from the population studies that 1362 nmol DFE/d is adequate to maintain normal folate status in pregnant women.

Folate status assessment.

This paper is a review of established methods of folate status assessment and the primary factors that increase the risk of folate deficiency, including physiological life cycle changes. The first stage of folate depletion can be assessed by measuring serum folate levels, which drop prior to tissue depletion, and which are paralleled by a reduction in red blood cell (RBC) folate. Functional changes associated with abnormalities in biochemical pathways can be monitored by the deoxyuridine suppression test. Cell division, including erythropoiesis, becomes impaired in the same time sequence as changes in biochemical functions, as evidenced by abnormal erythrocyte morphology and a reduction in hemoglobin concentration. In addition to inadequate dietary folate intake, key factors that may impair folate utilization and thus status include alcohol consumption, smoking, and specific drugs. Folate requirements may increase during various phases of the life cycle due to physiological stresses such as pregnancy and lactation. Folate status may also be compromised during adolescence and in senescence for diverse reasons that require special emphasis on factors such as biological maturity and socioeconomic status, as well as chronic use of alcohol, drugs, and smoking.