Folic acid

Folic acid
IUPAC name (2S)-2-[(4-{[(2-amino-4-hydroxypteridin-6-yl)methyl]amino}phenyl)formamido]pentanedioic acid
Other names N-​(4-​{[(2-​amino-​4-​oxo-​1,​4-​dihydropteridin-​6-​yl)​methyl]​amino}​benzoyl)-​L-​glutamic acid; pteroyl-L-glutamic acid; Vitamin B9; Vitamin M; Folacin
Identifiers
CAS number	59-30-3 Y
PubChem	6037
RTECS number	LP5425000
ATC code	B03BB01
SMILES C1=CC(=CC=C1C(=O)NC (CCC(=O)O)C(=O)O) NCC2=CN=C3C(=N2) C(=O)N=C(N3)N
Properties
Molecular formula	C19H19N7O6
Molar mass	441.4 g mol−1
Appearance	yellow-orange crystalline powder
Melting point	250 °C (523 K), decomp.
Solubility in water	0.0016 mg/ml (25 °C)
Acidity (pKa)	1st: 2.3, 2nd: 8.3
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Folic acid (also known as vitamin B₉^[1] or folacin) and folate (the naturally occurring form), as well as pteroyl-L-glutamic acid and pteroyl-L-glutamate, are forms of the water-soluble vitamin B₉. Folic acid is itself not biologically active, but its biological importance is due to tetrahydrofolate and other derivatives after its conversion to dihydrofolic acid in the liver.^[2]

Vitamin B₉ (folic acid and folate inclusive) is essential to numerous bodily functions ranging from nucleotide biosynthesis to the remethylation of homocysteine. The human body needs folate to synthesize DNA, repair DNA, and methylate DNA as well as to act as a cofactor in biological reactions involving folate.^[3] It is especially important during periods of rapid cell division and growth. Children and adults both require folic acid in order to produce healthy red blood cells and prevent anemia.^[4] Folate and folic acid derive their names from the Latin word folium (which means "leaf"). Leafy vegetables are a principal source, although, in Western diets, fortified cereals and bread may be a larger dietary source.

A lack of dietary folic acid leads to folate deficiency (FD). This can result in many health problems, the most notable one being neural tube defects in developing embryos. Low levels of folate can also lead to homocysteine accumulation as a result of the impairment of one-carbon metabolism mechanism methylation.^[3] DNA synthesis and repair are impaired and this could lead to cancer development.^[3] Supplementation in patients with ischaemic heart disease may, however, lead to increased rates of cancer and all-cause mortality.^[5]

A 2003 opinion article in the New York Times^[6] named micronutrients, especially folic acid, the "world's most luscious food," since absence of folic acid and a handful of other micronutrients causes otherwise preventable deformities and diseases, especially in fetal development. The article claims adding folic acid and micronutrients to the food supply of developing countries could be more cost effective than any other single action in improving world health.

Dietary reference intake

Because of the difference in bioavailability between supplemented folic acid and the different forms of folate found in food, the dietary folate equivalent (DFE) system was established. 1 DFE is defined as 1 μg (microgram) of dietary folate, or 0.6 μg of folic acid supplement.

Folate in foods and other sources

Certain foods are very high in folate:

• Leafy vegetables such as spinach, asparagus, turnip greens
• Legumes such as dried or fresh beans, peas and lentils
• Liver and liver products also contain high amounts of folate
• baker's yeast
• fortified grain products (pasta, cereal, bread); some breakfast cereals (ready-to-eat and others) are fortified with 25% to 100% of the recommended dietary allowance (RDA) for folic acid
• sunflower seeds

Moderate amounts:

• certain fruits (orange juice, canned pineapple juice, cantaloupe, honeydew melon, grapefruit juice, banana, raspberry, grapefruit, strawberry) and vegetables (beets, corn, tomato juice, vegetable juice, broccoli, brussels sprouts, romaine lettuce, bok choy),^[8] beer.^[9]

A table of selected food sources of folate and folic acid can be found at the USDA National Nutrient Database for Standard Reference.^[10] Folic acid is added to grain products in many countries, and, in these countries, fortified products make up a significant source of the population's folic acid intake.^[11] Because of the difference in bioavailability between supplemented folic acid and the different forms of folate found in food, the dietary folate equivalent (DFE) system was established. 1 DFE is defined as 1 μg of dietary folate, or 0.6 μg of folic acid supplement. This is reduced to 0.5 μg of folic acid if the supplement is taken on an empty stomach.^[12]

Folic acid naturally found in food is susceptible to high heat and UV, and is soluble in water.^[13] It is heat-labile in acidic environments and may also be subject to oxidation.^[13]

Some meal replacement products do not meet the folate requirements as specified by the RDAs.^[14]

Conversion to biologically active derivatives

All the biological functions of folic acid are performed by tetrahydrofolate and other derivatives. Their biological availability to the body depends upon dihydrofolate reductase action in the liver. This action is unusually slow in humans, being less than 2% of that in rats. Moreover, in contrast to rats, an almost-5-fold variation in the activity of this enzyme exists between humans.^[2] Due to this low activity, it has been suggested that this limits the conversion of folic acid into its biologically active forms "when folic acid is consumed at levels higher than the Tolerable Upper Intake Level (1 mg/d for adults)."^[2]

History

In the 1920s, scientists believed that folate deficiency and anemia were the same condition.^[15] A key observation by researcher Lucy Wills in 1931 led to the identification of folate as the nutrient needed to prevent anemia during pregnancy. Dr. Wills demonstrated that anemia could be reversed with brewer's yeast. Folate was identified as the corrective substance in brewer's yeast in the late 1930s and was first isolated in and extracted from spinach leaves by Mitchell and others in 1941.^[16] Bob Stokstad isolated the pure crystalline form in 1943, and was able to determine its chemical structure while working at the Lederle Laboratories of the American Cyanamid Company.^[17] This historical research project, of obtaining folic acid in a pure crystalline form in 1945, was done by the team called the "folic acid boys," under the supervision and guidance of Director of Research Dr. Yellapragada Subbarao, at the Lederley Lab, Pearl River, NY.^[18] This research subsequently led to the synthesis of the antifolate Aminopterin, the first-ever anti-cancer drug, the clinical proof of its efficacy was proven by Dr. S. Farber in 1948. In the 1950s and 1960s, scientists began to discover the biochemical mechanisms of action for folate.^[15] In 1960 experts first linked folate deficiency to neural tube defects.^[15] In the late 1990s, US scientists realized that, despite the availability of folate in foods and in supplements, there was still a challenge for people to meet their daily folate requirements, which is when the US implemented the folate fortification program.^[15]

Biological roles

A diagram of the chemical structure of folate.

DNA and cell division

Folate is necessary for the production and maintenance of new cells, for DNA synthesis and RNA synthesis, and for preventing changes to DNA, and, thus, for preventing cancer.^[19] It is especially important during periods of rapid cell division and growth such as infancy and pregnancy. Folate is needed to carry one-carbon groups for methylation reactions and nucleic acid synthesis (the most notable one being thymine, but also purine bases).^[20] Thus, folate deficiency hinders DNA synthesis and cell division, affecting hematopoietic cells and neoplasms the most because of rapid cell division. RNA transcription, and subsequent protein synthesis, are less affected by folate deficiency, as the mRNA can be recycled and used again (as opposed to DNA synthesis, where a new genomic copy must be created). Since folate deficiency limits cell division, erythropoiesis, production of red blood cells is hindered and leads to megaloblastic anemia, which is characterized by large immature red blood cells. This pathology results from persistently thwarted attempts at normal DNA replication, DNA repair, and cell division, and produces abnormally large red cells called megaloblasts (and hypersegmented neutrophils) with abundant cytoplasm capable of RNA and protein synthesis, but with clumping and fragmentation of nuclear chromatin. Some of these large cells, although immature (reticulocytes), are released early from the marrow in an attempt to compensate for the anemia.^[21] Both adults and children need folate to make normal red and white blood cells and prevent anemia.^[22] Deficiency of folate in pregnant women has been implicated in neural tube defects (NTD); therefore, many developed countries have implemented mandatory folic acid fortification in cereals, etc. It must be noted that NTDs occur early in pregnancy (first month), therefore women must have abundant folate upon conception. Folate is required to make red blood cells and white blood cells and folate deficiency may lead to anemia, which further leads to fatigue and weakness and inability to concentrate.^[23]

Biochemistry of DNA base and amino acid production

Metabolism of folic acid to produce methyl-vitamin B₁₂

In the form of a series of tetrahydrofolate (THF) compounds, folate derivatives are substrates in a number of single-carbon-transfer reactions, and also are involved in the synthesis of dTMP (2′-deoxythymidine-5′-phosphate) from dUMP (2′-deoxyuridine-5′-phosphate). It is a substrate for an important reaction that involves vitamin B₁₂ and it is necessary for the synthesis of DNA, and so required for all dividing cells.^[24]

The pathway leading to the formation of tetrahydrofolate (FH₄) begins when folate (F) is reduced to dihydrofolate (DHF) (FH₂), which is then reduced to THF. Dihydrofolate reductase catalyses the last step.^[25] Vitamin B₃ in the form of NADPH is a necessary cofactor for both steps of the synthesis.

Methylene-THF (CH₂FH₄) is formed from THF by the addition of methylene groups from one of three carbon donors: formaldehyde, serine, or glycine. Methyl tetrahydrofolate (CH₃-THF) can be made from methylene-THF by reduction of the methylene group with NADPH. It is important to note that Vitamin B₁₂ is the only acceptor of methyl-THF. There is also only one acceptor for methyl-B₁₂, which is homocysteine in a reaction catalyzed by homocysteine methyltransferase. This is important because a defect in homocysteine methyltransferase or a deficiency of B₁₂ can lead to a methyl-trap of THF and a subsequent deficiency.^[17] Thus, a deficiency in B₁₂ can generate a large pool of methyl-THF that is unable to undergo reactions and will mimic folate deficiency. Another form of THF, formyl-THF or folinic acid results from oxidation of methylene-THF or is formed from formate donating formyl group to THF. Finally, histidine can donate a single carbon to THF to form methenyl-THF.

In other words:

folate → dihydrofolate → tetrahydrofolate ↔ methylene-THF → methyl-THF

Overview of drugs that interfere with folate reactions

A number of drugs interfere with the biosynthesis of folic acid and THF. Among them are the dihydrofolate reductase inhibitors such as trimethoprim, pyrimethamine, and methotrexate; the sulfonamides (competitive inhibitors of 4-aminobenzoic acid in the reactions of dihydropteroate synthetase).

The National Health and Nutrition Examination Survey (NHANES III 1988–91) and the Continuing Survey of Food Intakes by Individuals (1994–96 CSFII) indicated that most adults did not consume adequate folate.^[26][27] However, the folic acid fortification program in the United States has increased folic acid content of commonly eaten foods such as cereals and grains, and as a result diets of most adults now provide recommended amounts of folate equivalents.^[28]

Health issues

Human reproduction

Folic acid is an important nutrient for women who may become pregnant, because a woman's blood levels of folate fall during pregnancy due to an increased maternal RBC synthesis in the first half of the pregnancy and fetal demands in the second half.^[7] The first four weeks of pregnancy (when most women do not even realize they are pregnant) require folic acid for proper development of the brain, skull, and spinal cord.^[8] Serious birth defects like neural tube defects are less likely to occur when women take 0.4 mg of folic acid daily.^[8] Adequate folate intake during the preconception period, the time right before and just after a woman becomes pregnant, helps protect against a number of congenital malformations including neural tube defects (which are the most notable birth defects that occur from folate deficiency).^[29] Neural tube defects (NTDs) result in malformations of the spine (spina bifida), skull, and brain (anencephaly). The risk of neural tube defects is significantly reduced when supplemental folic acid is consumed in addition to a healthy diet prior to and during the first month following conception.^[30][31] The protective effect of folate during pregnancy goes beyond NTDs. Supplementation with folic acid has been shown to reduce the risk of congenital heart defects, cleft lip,^[32] limb defects, and urinary tract anomalies.^[33] Women who could become pregnant are advised to eat foods fortified with folic acid or take supplements in addition to eating folate-rich foods to reduce the risk of some serious birth defects. Having enough folic acid supplements in the months before pregnancy is very important to prevent neural tube defects.^[34] Taking 400 micrograms of synthetic folic acid daily from fortified foods and/or supplements has been suggested. The RDA for folate equivalents for pregnant women is 600-800 micrograms, twice the normal RDA of 400 micrograms for women who are not pregnant.^[35]

A study published by Milunski et al. has indicated that women that take folic acid supplements during the course of pregnancy can dramatically reduce the prevalence of infant neural tube defects by 3.9 times. The prevalence had dropped from 3.5 to 0.9 defects per 1000 births.^[36]

Although the recommended folic acid intake for women planning for pregnancy is 400 micrograms per day, the mechanisms and reasons why folic acid prevents birth defects is unknown.^[37] It is hypothesized that the insulin-like growth factor 2 gene is differentially methylated and these changes in IGF2 result in improved intrauterine growth and development.^[37]

Folate deficiency during pregnancy can increase the risk of preterm delivery, infant low birth weight, and fetal growth retardation.^[38] Folate deficiency in the mother increases homocysteine level in the blood, which may lead to spontaneous abortion and pregnancy complications such as placental abruption and preeclampsia.^[38]

Recent studies have been conducted to test the hypothesis that folic acid supplementation reduces the risk of childhood acute lymphoblastic leukemia, but evidence so far has been weak.^[39]

Folic acid may also reduce chromosomal defects in sperm to some extent, which may be relevant for men considering to father a child.^[40] A benefit is indicated even for more than 700 mcg folate per day,^[40] which, though below the tolerable upper intake levels of 1,000 µg/day, was 1.8 times the recommended dietary allowance.

It is estimated that approximately 85% of women use folic acid supplements before they become pregnant, but only 18% use enough folic acid supplements to meet the current folic acid requirements due to socio-economic challenges facing some women.^[41]

Folic acid supplements may even protect the fetus against disease when the mother is battling a disease or taking medications or smoking during pregnancy.^[42]

Heart disease

An estimated 13,500 deaths occur annually due to folate deficiency's effect on coronary artery disease and the risk of ischemic heart disease, and stroke has been reduced by 15% since folate fortification regulations were enforced.^[43] Adequate concentrations of folate, vitamin B₁₂, or vitamin B₆ may decrease the circulating level of homocysteine, an amino acid normally found in blood. There is evidence that an elevated homocysteine level is an independent risk factor for heart disease and stroke.^[44] The evidence suggests that high levels of homocysteine may damage coronary arteries or make it easier for blood clotting cells called platelets to clump together and form a clot.^[45] However, there is currently no evidence available to suggest that lowering homocysteine with vitamins will reduce risk of heart disease. The NORVIT trial suggests that folic acid supplementation may do more harm than good.^[46]

As of 2006, studies have shown that giving folic acid to reduce levels of homocysteine does not result in clinical benefit. One of these studies suggests that folic acid in combination with B₁₂ may even increase some cardiovascular risks.^[47][48][49]

However, a 2005 study found that 5 mg of folate daily over a three-week period reduced pulse pressure by 4.7 mmHg compared with a placebo, and concluded that^[50]

Folic acid is a safe and effective supplement that targets large artery stiffness and may prevent isolated systolic hypertension.

Also, as a result of new research, "heart experts" at Johns Hopkins Medical Center reported in March 2008 ^[51] in favour of therapeutic folate, although they cautioned that it is premature for people to begin to self-medicate by taking high doses of folic acid."

Hyperhomocysteinemia is a predictor of cardiovascular disease and hypertension among children and folic acid is a safe and effective supplement because it reduces serum homocysteine levels as well as systolic and diastolic blood pressure, thus preventing cardiovascular disease in children.^[52]

Folic acid supplements may improve the integrity of the vascular endothelium.^[53] Folic acid supplements consumed before and during pregnancy may reduce the risk of heart defects in infants.^[54] Folic acid supplementation may reduce the risk of children's developing metabolic syndrome.^[55] Folic acid supplements may worsen the outcomes in patients with cardiovascular disease such as angina and myocardial infarction.^[56]

Stroke

Folic acid appears to reduce the risk of stroke. The reviews indicate only that in some individuals the risk of stroke appears to be reduced, but a definite recommendation regarding supplementation beyond the current recommended daily allowance has not been established for stroke prevention.^[57] Observed stroke reduction is consistent with the reduction in pulse pressure produced by folate supplementation of 5 mg per day, since hypertension is a key risk factor for stroke. Folic supplements are inexpensive and relatively safe to use and that is why stroke or hyperhomocysteinemia patients are encouraged to consume daily B vitamins including folic acid.^[58]

Cancer

Folate deficiency decreases intracellular S-adenosylmethionine (SAM), which inhibits cytosine methylation in DNA, activates proto-oncogenes, induces malignant transformations, causes DNA precursor imbalances, misincorporates uracil into DNA, and promotes chromosome breakage; all of these mechanisms increase the risk of prostate cancer development.^[59]

The association between folate and cancer appears to be complex.^[60] Even though theoretically it has been suggested that folate may help prevent cancer^[61] actual trials have found that supplementation increases rates of cancer.^[5]

Some investigations have proposed that good levels of folic acid may be related to lower risk of esophageal, stomach, and ovarian cancers, but the benefits of folic acid against cancer may depend on when it is taken and on individual conditions. In addition, folic acid may not be helpful, and could even be damaging, in people already suffering from cancer or from a precancerous condition. On the converse, it has been suggested that excess folate may promote tumor initiation.^[62] Folate has shown to play a dual role in cancer development; low folate intake protects against early carcinogenesis but high folate intake promotes advanced carcinogenesis.^[63] Therefore, public health recommendations should be careful not to encourage too much folate intake.^[63]

Diets great in folate are associated with decreased risk of colorectal cancer; some studies show an association that is stronger for folate from foods alone than for folate from foods and supplements,^[64] while other studies find that folate from supplements is more effective due to greater bioavailability.^[65] A 2007 randomized clinical trial found that folate supplements did not reduce the risk of colorectal adenomas, but do in fact increase the presence of advanced lesions and adenoma multiplicity.^[66] Colorectal cancer is the most studied type of cancer in relation to folate and one carbon metabolism and most research studies associate high folate intake with a reduced risk of prostate cancer.^[67] However, folic acid supplement intake increased advanced colorectal cancer development by 67% in a 14 year European research study involving 520,000 men.^[68]

A 2006 prospective study of 81,922 Swedish adults found that diets great in folate from foods, but not from supplements, were associated with a reduced risk of pancreatic cancer.^[69]

Most epidemiologic studies suggest that diets high in folate are associated with decreased risk of breast cancer, but results are not uniformly consistent: One broad cancer screening trial reported a potential harmful effect of much folate intake on breast cancer risk, suggesting that routine folate supplementation should not be recommended as a breast cancer preventive,^[70] but a 2007 Swedish prospective study found that much folate intake was associated with a lower incidence of postmenopausal breast cancer.^[71] A 2008 study has shown no significant effect of folic acid on overall risk of total invasive cancer or breast cancer among women.^[72] Folate intake may not have any effect on the risk of breast cancer but may have an effect for women who consume at least 15 g/d of alcohol.^[73] Folate intake of more than 300 µg/d may reduce the risk of breast cancer in women who consume alcohol.^[73]

In men, folic acid supplementation appears to double the risk of prostate cancer.^[74] Recently, a clinical trial showed that daily supplementation of 1 mg of folic acid increased the risk of prostate cancer while dietary and plasma folate levels among non vitamin users actually decreased the risk of prostate cancer.^[75] The reasons why high levels of folic acid may increase cancer is because of its role in nucleotide synthesis (proliferating neoplastic cells need this and folate receptors are increased in cancers).^[76] Folate's role in DNA methylation is important in prostate cancer.^[77] Unmetabolized folic acid is associated with a reduction in natural killer cell cytotoxicity, which reduces the immune system's ability to defend against malignant cells.^[78] However, the study also showed that dietary baseline intake of folate may have inverse effects of prostate cancer.

The cancer drug methotrexate is designed to inhibit the metabolism of folic acid. Folic acid may interact unexpectedly with the cancer drug fluorouracil. The exact mechanism of interaction is unknown.^[79]

The low dihydrofolate reductase activity in the liver of humans compared to other animals and so the low conversion of folic acid into its active derivatives might be due to the control of this enzyme by transcription factors such as E2F-1 involved in cell proliferation. It has been suggested that "the low level of DHFR, and the other proteins under the control of E2F-1, in humans may have evolved to hinder the development of cancer. If this is the case, other animals with slow tissue turnover rates, possibly related to long life span, might also have low DHFR activity."^[2]

Although the relationship between folate and prostate cancer is not yet clear, there have been suicide gene studies that show a target vector for folate to prostate and nasopharyngeal cancer cells.^[80] Growth of tumor cells is significantly inhibited when a folate-linked nanoparticle is injected intratumorally.^[80] The mechanism might be the interference of transfection and communication failures of intracellular gap junctions.^[80]

A Finnish study consisting of 29,133 older male smokers resulted in the observation that prostate cancer risk had no relationship with serum folate levels.^[3]

Folic acid supplements prevent mistakes from occurring during DNA replication and repair, for example the mistake of inserting uracils into the DNA.^[81] This is a proposed mechanism for folic acid's protection against colorectal cancer.^[81]

Folic acid supplements stimulate the PI3k/Akt signaling cascade, which leads to improved cell survival but this could be beneficial or harmful for the body because cancer cells may use this pathway to survive.^[82] Folic acid may also reduce the levels of PTEN (a tumor suppressor gene), making this relationship even more controversial.^[82]

Antifolates

Folate is important for cells and tissues that rapidly divide.^[19] Cancer cells divide rapidly, and drugs that interfere with folate metabolism are used to treat cancer. The antifolate methotrexate is a drug often used to treat cancer because it inhibits the production of the active form of THF from the inactive dihydrofolate (DHF). However, methotrexate can be toxic,^[83][84][85] producing side-effects such as inflammation in the digestive tract that make it difficult to eat normally. Also, bone marrow depression (inducing leukopenia and thrombocytopenia), acute renal, and hepatic failure have been reported.

Folinic acid, under the drug name leucovorin, is a form of folate (formyl-THF) that can help "rescue" or reverse the toxic effects of methotrexate.^[86] Folinic acid is not the same as folic acid. Folic acid supplements have little established role in cancer chemotherapy.^[87][88] There have been cases of severe adverse effects of accidental substitution of folic acid for folinic acid in patients receiving methotrexate cancer chemotherapy. It is important for anyone receiving methotrexate to follow medical advice on the use of folic or folinic acid supplements. The supplement of folinic acid in patients undergoing methotrexate treatment is to give non-rapidly dividing cells enough folate to maintain normal cell functions. The amount of folate given will be depleted by rapidly dividing cells (cancer) very fast and so will not negate the effects of methotrexate.

Obesity

Folic acid increases lipolysis in adipocytes and may have a role in the prevention of obesity and type 2 diabetes.^[89] This mechanism involves the beta adrenoceptors in the adbdominal adipocytes.^[90] Folic acid supplements may reduce the accumulation of cholesterol in the liver and in the blood; this may be due to folic acid's role in incorporating cholesterol into bile acid.^[91] Folic acid supplements have been shown to increase bile acid production and flow.^[92]

Depression

Some evidence links a shortage of folate with depression.^[93] There is some limited evidence from randomised controlled trials that using folic acid in addition to antidepressants, specifically SSRIs, may have benefits.^[94] Research at the University of York and Hull York Medical School has found a link between depression and low levels of folate.^[95] One study by the same team involved 15,315 subjects.^[96] However, the evidence is probably too limited at present for this to be a routine treatment recommendation. Folic acid supplementation affects noradrenaline and serotonin receptors within the brain and this could be the cause of folic acid's possible ability to act as an antidepressant.^[97]

Memory and mental agility

In a 3-year trial on 818 people over the age of 50, short-term memory, mental agility, and verbal fluency were all found to be better among people who took 800 micrograms of folic acid daily, twice the current RDA, than those who took placebo. The study was reported in The Lancet on 20 January 2007.^[98]

Schizophrenia

Folate deficiency may increase the risk of schizophrenia because by increasing homocysteine levels folate also increases interleukin 6 and tumor necrosis factor alpha levels and these two cytokines are involved in the development of schizophrenia.^[99] The exact mechanisms involved in the development of schizophrenia are not entirely clear but may have something to do with DNA methylation and one carbon metabolism and these are the precise roles of folate in the body and that is why folate deficiency has been linked to schizophrenia.^[100]

Allergic diseases

There is a relationship between folic acid and allergic diseases.^[101] In one study that examined the relationship between serum folate levels and markers of atopy, wheeze, and asthma in 8083 subjects serum folate levels were found to be inversely related to IgE level, atopy, and wheeze in a dose-response relationship.^[102] Increased folate levels were also associated with decreased risk of doctor-diagnosed asthma.^[103] Folic acid supplementation during late pregnancy is associated with an increased risk of childhood asthma, increased risk of persistent asthma, and poorer respiratory function in young children.^[104]

Rheumatoid arthritis

Folic acid supplementation of 5–27 mg per week has shown to have a protective effect against rheumatoid arthritis.^[105]

Fertility

Folate is necessary for fertility in both men and women. In men, it contributes to spermatogenesis. In women, on the other hand, it contributes to oocyte maturation, implantation, placentation, in addition to the general effects of folic acid and pregnancy. Therefore, it is necessary to receive sufficient amounts through the diet, in order to avoid subfertility.^[106] Also, polymorphisms in genes of enzymes involved in folate metabolism could be one reason for fertility complications in some women with unexplained infertility.^[107]

Renal disease

Folic acid supplements may reduce the risk of children developing renal diseases or injuries such as microalbuminuria.^[108]

Type 1 diabetes mellitus

Type 1 diabetes mellitus patients have lower plasma levels of folic acid and may benefit from folic acid supplements or folic acid fortified food products.^[109]

Macular degeneration

A substudy of the Women's Antioxidant and Folic Acid Cardiovascular Study published in 2009 reports that use of a nutritional supplement that contains folic acid, pyridoxine, and cyanocobalamin decreased the risk of developing age-related macular degeneration by 34.7%.^[110]

Bone health

It has been hypothesized that folate deficiency can lead to elevated homocysteine levels, which, in turn, leads to an increased risk of bone fractures, osteoporosis, and reduction in BMD but research studies so far show controversial results.^[111]

Menopause

Folic acid supplements help relieve hot flushes in postmenopausal women.^[97] Just like in estrogen hormone replacement therapy, folic acid interacts with neurotransmitters (norepinephrine, serotonin) in the brain to reduce hot flushes.^[97]

Infectious disease

Folate deficiency is linked to anemia causing Plasmodium falciparum malaria in areas such as Colombia where malaria has reached endemic proportions.^[112]

Bone loss in Parkinson's disease (PD)

Folate lowers homocysteine (Hcy) levels, which, in turn, prevents bone loss in Parkinson's disease (PD) patients taking levodopa (a psychoactive drug taken to treat Parkinson's disease).^[113] Improvements in bone health include increased BMD at the lumbar spine, total femur, and femur shaft.^[114]

Folic acid supplements and masking of B₁₂ deficiency

There has been concern about the interaction between vitamin B₁₂ and folic acid.^[115] Folic acid supplements can correct the anemia associated with vitamin B₁₂ deficiency. Unfortunately, folic acid will not correct changes in the nervous system that result from vitamin B₁₂ deficiency. Permanent nerve damage could theoretically occur if vitamin B₁₂ deficiency is not treated. Therefore, intake of supplemental folic acid should not exceed 1000 micrograms (1000 µg = 1 mg) per day to prevent folic acid from masking symptoms of vitamin B₁₂ deficiency. In fact, to date the evidence that such masking actually occurs is scarce, and there is no evidence that folic acid fortification in Canada or the U.S. has increased the prevalence of vitamin B₁₂ deficiency or its consequences.^[116]

However, one recent study has demonstrated that high folic or folate levels, when combined with low B₁₂ levels, are associated with significant cognitive impairment among the elderly.^[117]

In any case, it is important for older adults to be aware of the relationship between folic acid and vitamin B₁₂, because they are at greater risk of having a vitamin B₁₂ deficiency. Patients 50 years of age or older should ask their physicians to check their vitamin B₁₂ status before taking a supplement that contains folic acid.^[118]

Overdose Risks

The risk of toxicity from folic acid is low because folate is a water-soluble vitamin and is regularly removed from the body through urine.^[119] The Institute of Medicine has established a tolerable upper intake level (UL) for folate of 1 mg for adult men and women, and a UL of 800 µg for pregnant and lactating (breast-feeding) women less than 18 years of age. Supplemental folic acid should not exceed the UL to prevent folic acid from masking symptoms of vitamin B₁₂ deficiency.^[120]

Research suggests high levels of folic acid can interfere with some antimalarial treatments.^[121]

A 10,000-patient study at Tufts University in 2007 concluded that excess folic acid worsens the effects of B₁₂ deficiency and in fact may affect the absorption of B₁₂.^[122]

A study at the University of Adelaide concluded that the intake of folic acid supplements during late pregnancy increases the risk of babies developing childhood asthma by 30%, although researchers emphasized that their finding did not contradict recommendations to supplement folic acid in first trimester, when no additional risk was found.^[123]

Elderly population

There are benefits and risks of food folic acid fortification for elderly populations.^[124] Elevated exposure to folic acid due to fortification can improve folate and homocysteine levels but can also mask symptoms of vitamin B₁₂ deficiency.^[124] A study where 747 subjects aged 67 to 96 years were measured for B vitamin and homocysteine status showed that diets with folic acid fortification of 140 µg/100 g of grain product decreased homocysteine level and heart disease risk.^[124] However, Canada's food supply is fortified with 150 µg/100 g of grain and much of the elderly population also take a supplement that includes a folic acid component of 400 µg. Therefore, it is important not to consume quantities over the recommended DRI.

Folate deficiency

Folate deficiency may lead to glossitis, diarrhea, depression, confusion, anemia, and fetal neural tube defects and brain defects (during pregnancy).^[125] Folate deficiency is diagnosed by analyzing CBC and plasma vitamin B₁₂ and folate levels.^[125] CBC may indicate megaloblastic anemia but this could also be a sign of vitamin B₁₂ deficiency.^[125] A serum folate of 3 μg/L or lower indicates deficiency.^[125] Serum folate level reflects folate status but erythrocyte folate level better reflects tissue stores after intake.^[125] An erythrocyte folate level of 140 μg/L or lower indicates inadequate folate status.^[125] Increased homocysteine level suggests tissue folate deficiency but homocysteine is also affected by vitamin B₁₂ and vitamin B₆, renal function, and genetics.^[125] One way to differentiate between folate deficiency from vitamin B₁₂ deficiency is by testing for methylmalonic acid levels.^[125] Normal MMA levels indicate folate deficiency and elevated MMA levels indicate vitamin B₁₂ deficiency.^[125] Folate deficiency is treated with supplemental oral folate of 400 to 1000 μg per day.^[125] This treatment is very successful in replenishing tissues even if deficiency was caused by malabsorption.^[125] Patients with megaloblastic anemia need to be tested for vitamin B₁₂ deficiency before folate treatment because if the patient has vitamin B₁₂ deficiency, folate supplementation can remove the anemia but can also worsen neurologic problems.^[125] Morbidly obese patients with BMIs of greater than 50 are more likely to develop folate deficiency.^[126] Patients with celiac disease have a higher chance of developing folate deficiency.^[126] Cobalamin deficiency may lead to folate deficiency, which, in turn, increases homocysteine levels and finally may result in the development of cardiovascular disease or birth defects.^[127]

Iron-Folic acid supplementation risk for children

Some studies show that iron-folic acid supplementation in children under 5 may result in increased mortality due to malaria; this has prompted the World Health Organization to alter their iron-folic acid supplementation policies for children in malaria prone areas such as India.^[128]

Dietary fortification

In the USA many grain products are fortified with folic acid.

Since the discovery of the link between insufficient folic acid and neural tube defects (NTDs), governments and health organizations worldwide have made recommendations concerning folic acid supplementation for women intending to become pregnant.

This has led to the introduction in many countries of fortification, where folic acid is added to flour with the intention of everyone's benefiting from the associated rise in blood folate levels. This is controversial, with issues having been raised concerning individual liberty , and the masking effect of folate fortification on pernicious anaemia (vitamin B₁₂ deficiency). However, several western countries now fortify their flour, along with a number of Middle Eastern countries and Indonesia. Mongolia and a number of ex-Soviet republics are among those having widespread voluntary fortification; about five more countries (including Morocco, the first African country) have agreed but not yet implemented fortification. To date, no EU country has yet mandated fortification.^[129]

Folates can be produced by engineering Lactococcus lactis strains using a rodent depletion-repletion bioassay, and the bioavailabilities of these folates are comparable with those of commercial folic acid currently being used for food fortification.^[130] These engineered folates can potentially help alleviate the effects of folate deficiency in the diet.^[131] Hematologic studies show an improvement in megaloblastic anemia after the addition of L. lactis strains; this again suggests that lactic acid bacteria can potentially reverse some of the harm done by folate deficiency by acting as an essential, bioavailable vitamin.^[132]

Effects of fortification and plasma folate and homocysteine levels

A study has shown that folate fortification will substantially increase in folate status, in particular, for the elderly. In the study group, the subjects that did not use vitamin supplements has increased folate concentrations of 4.6 ng/mL to 10.0 ng/mL (11 to 23 nmol/L) (P<0.001) from the base-line visit to the follow-up visit. The prevalence of low folate concentrations (<3 ng/mL [7 nmol/L]) decreased from 22.0% to 1.7% (P< 0.001). The mean total homocysteine concentration has decreased from a value of 10.1 µmol/L to 9.4 µmol/L during this period (P<0.001), while the prevalence of high homocysteine concentrations (>13 µmol/L) has been reduced from 18.7% to 9.8% (P<0.001). To further clarify the study methods, there were no statistically significant changes in concentrations of folate or homocysteine for the control group.^[133]

Australia

There has been previous debate in Australia regarding the inclusion of folic acid in products such as bread and flour.^[134]

Australia and New Zealand have jointly agreed to fortification though the Food Standards Australia New Zealand. Australia will fortify all flour from 18 September 2009.^[135] Although the food standard covers both Australia and New Zealand, an Australian government official has stated it is up to New Zealand to decide whether to implement it in New Zealand, and they will watch with interest.^[136]

The requirement is 0.135 mg of folate per 100g of bread.

Canada

In 2003, a Hospital for Sick Children, University of Toronto research group published findings showing that the fortification of flour with folic acid in Canada has resulted in a dramatic decrease in neuroblastoma, an early and very dangerous cancer in young children.^[137] In 2009, further evidence from McGill University showed a 6.2% decrease per year in the birth prevalence of severe congenital heart defects.^[138]

Folic acid used in fortified foods is a synthetic form called pteroylmonoglutamate.^[139] It is in its oxidized state and contains only one conjugated glutamate residue.^[139] Folic acid therefore enters via a different carrier system than naturally occurring folate and this may have different effects on folate binding proteins and its transporters.^[140] Folic acid has a higher bioavailability than natural folates and are rapidly absorbed across the intestine,^[139] therefore it is important to consider the Dietary Folate Equivalent (DFE) when calculating your intake. Natural occurring folate is equal to 1 DFE, however 0.6 µg of folic acid is equal to 1 DFE.

Folic acid food fortification became mandatory in Canada in 1998, with the fortification of 150 µg of folic acid per 100 grams of enriched flour and uncooked cereal grains.^[141] The purpose of fortification was to decrease the risk of neural tube defects in newborns.^[141] It is important to fortify grains because it is a widely eaten food and the neural tube closes in the first four weeks of gestation, often before many women even know they are pregnant. Canada's fortification program has been successful with a decrease of neural tube defects by 19% since its introduction.^[142] A seven-province study from 1993 to 2002 showed a reduction of 46% in the overall rate of neural tube defects after folic acid fortification was introduced in Canada.^[143] The fortification program was estimated to raise a person’s folic acid intake level by 70–130 µg/day, however an increase of almost double that amount was actually observed.^[142] This could be from the fact that many foods are over fortified by 160–175% the predicted value.^[142] In addition, much of the elder population take supplements that adds 400 µg to their daily folic acid intake. This is a concern because 70-80% of the population have detectable levels of unmetabolized folic acid in their blood and high intakes can accelerate the growth of preneoplasmic lesions.^[144] It is still unknown the amount of folic acid supplementation that might cause harm.^[141]

Folic acid supplementation promotion in Canada

According to a Canadian survey, 58% of women said they took a folic acid containing multivitamin or a folic acid supplement as early as three months before becoming pregnant.^[143] Women in higher income households and with more years of school education are using more folic acid supplements before pregnancy.^[143] Women with planned pregnancies and who are over the age of 25 are more likely to use folic acid supplements.^[143] Canadian public health efforts are focused on promoting awareness of the importance of folic acid supplementation for all women of childbearing age and decreasing socio-economic inequalities by providing practical folic acid support to vulnerable groups of women.^[143]

New Zealand

New Zealand was going to fortify bread (excluding organic and unleavened varieties) from 18 September 2009 but has opted to wait until more research is done.^[135]

The Association of Bakers ^[145] and the Green Party ^[146] have opposed mandatory fortification, describing it as "mass medication". Food Safety Minister Kate Wilkinson reviewed the decision to fortify in July 2009, citing links between overconsumption of folate with cancer .^[147] The New Zealand Government is reviewing whether it will continue with the mandatory introduction of folic acid to bread.^[148]

United Kingdom

There has been previous debate in the United Kingdom regarding the inclusion of folic acid in products such as bread and flour.^[149]

The Food Standards Agency has recommended fortification.^{[150][151][152]}

United States

The United States Public Health Service recommends an extra 0.4 mg/day, which can be taken as a pill. However, many researchers believe that supplementation in this way can never work effectively enough, since about half of all pregnancies in the U.S. are unplanned and not all women will comply with the recommendation. Approximately 53% of the US population uses dietary supplements and 35% uses dietary supplements containing folic acid.^[153] Men consume more folate (in dietary folate equivalents) than women and non-Hispanic whites have higher folate intakes than Mexican Americans and non-Hispanic blacks.^[153] Twenty nine percent of black women have inadequate intakes of folate.^[153] The age group consuming the most folate and folic acid is the >50 group.^[153] Only 5% of the population exceeds the Tolerable Upper Intake Level.^[153]

In 1996, the United States Food and Drug Administration (FDA) published regulations requiring the addition of folic acid to enriched breads, cereals, flours, corn meals, pastas, rice, and other grain products.^[154][155] This ruling took effect on January 1, 1998, and was specifically targeted to reduce the risk of neural tube birth defects in newborns.^[156] There are concerns that the amount of folate added is insufficient .^[157] In October 2006, the Australian press claimed that U.S. regulations requiring fortification of grain products were being interpreted as disallowing fortification in non-grain products, specifically Vegemite (an Australian yeast extract containing folate). The FDA later said the report was inaccurate, and no ban or other action was being taken against Vegemite.^[158]

As a result of the folic acid fortification program, fortified foods have become a major source of folic acid in the American diet. The Centers for Disease Control and Prevention in Atlanta, Georgia used data from 23 birth defect registries that cover about half of United States births, and extrapolated their findings to the rest of the country. These data indicate that since the addition of folic acid in grain-based foods as mandated by the FDA, the rate of neural tube defects dropped by 25% in the United States.^[159] The results of folic acid fortification on the rate of neural tube defects in Canada have also been positive, showing a 46% reduction in prevalence of NTDs;^[160] the magnitude of reduction was proportional to the prefortification rate of NTDs, essentially removing geographical variations in rates of NTDs seen in Canada before fortification.

When the U.S. Food and Drug Administration set the folic acid fortification regulation in 1996, the projected increase in folic acid intake was 100 µg/d.^[161] Data from a study with 1480 subjects showed that folic acid intake increased by 190 µg/d and total folate intake increased by 323 µg dietary folate equivalents (DFE)/d.^[161] Folic acid intake above the upper tolerable intake level (1000 µg folic acid/d) increased only among those individuals consuming folic acid supplements as well as folic acid found in fortified grain products.^[161] Taken together, folic acid fortification has led to a bigger increase in folic acid intake than first projected.^[161]

Future directions for research

• Identifying polymorphisms or mutations in genes involved in the synthesis of thymidylate, purines, regulatory proteins, or substrates involved in folate and homocysteine metabolism, such as serine hydroxymethyltransferase and methylenetetrahydrofolate dehydrogenase, rather than simply focusing on 5,10-methylenetetrahydrofolate reductase as the main cause .^[162]
• Direct/ Indirect look at the adverse effects of our greatly increased folic acid intakes
• Human studies looking into whether folate will interfere with the effectiveness of antifolate treatments and the possibility that it may support cancer growth^[163]
• More epidemiologic and clinical studies are need to be done on human tumor sample to fully understand the role of folate receptor alpha in tumor etiology, progression, and patient survival.^[164]

See also

• Dietary supplement

References

Bibliography

• This article contains information from the public domain resource at http://www.cc.nih.gov/ccc/supplements/folate.html
• Herbert V (1999). "Folic Acid". In Shils ME, Olson J, Shike M, Ross AC. Modern nutrition in health and disease (9th ed.). Baltimore: Williams and Wilkins. ISBN 0-683-30769-X. 
• Food and Nutrition Board, Institute of Medicine (1998). Dietary reference intakes for thiamin, riboflavin, niacin, vitamin B₆, folate, vitamin B₁₂, pantothenic acid, biotin, and choline / a report of the Standing Committee on the Scientific Evaluation of Dietary Reference Intakes and its Panel on Folate, Other B Vitamins, and Choline and Subcommittee on Upper Reference Levels of Nutrients. Washington, D.C.: National Academy Press. ISBN 0-309-06554-2. 
• Dietary Guidelines Advisory Committee, Agricultural Research Service, United States Department of Agriculture (USDA). Report of the Dietary Guidelines Advisory Committee on the Dietary Guidelines for Americans, 2000. http://www.ars.usda.gov/dgac

External links

• Jane Higdon, "Folic Acid", Micronutrient Information Center, Linus Pauling Institute
• Health Canada article about folic acid
• US Public Health Service information page on folic acid
• Oakley GP (June 2002). "Delaying folic acid fortification of flour". BMJ 324 (7350): 1348–9. doi:10.1136/bmj.324.7350.1348. PMID 12052788. PMC 1123313. http://bmj.com/cgi/content/full/324/7350/1348. 
• Salvi VS (1 July 2003). "Folic acid and birth defects". J Postgrad Med 49 (3): 195–6. PMID 14597778. http://www.jpgmonline.com/article.asp?issn=0022-3859;year=2003;volume=49;issue=3;spage=195;epage=196;aulast=Salvi. 
• Folic Acid The Vitamin That Does Almost Everything-U.C Berkeley Wellness Letter April 2003
• BMC Pregnancy and Childbirth 2004: no vitamin B₁₂ problems in Canada after folic acid fortification
• The primary prevention of birth defects: Multivitamins or folic acid?
• Mills JL, Von Kohorn I, Conley MR, et al. (1 June 2003). "Low vitamin B₁₂ concentrations in patients without anemia: the effect of folic acid fortification of grain". Am J Clin Nutr. 77 (6): 1474–7. PMID 12791626. http://www.ajcn.org/cgi/pmidlookup?view=long&pmid=12791626. "Despite evidence that folic acid exposure has increased dramatically since food fortification began, this population showed no evidence of an increase in low vitamin B₁₂ concentrations without anemia. If confirmed, these results would indicate that food fortification has not caused a major increase in masking of vitamin B₁₂ deficiency.". 
• Folic acid may help prevent throat cancer
• Polymorphisms Affecting Red Cell Folate Concentrations in Women could Identify Increased Risk for certain Birth Defects

Biochemistry links

• Folate biosynthesis (early stages)
• Folate biosynthesis (later stages)
• Folate coenzymes
• C₁ metabolism with folate
• Formylation, hydroxymethylation and methylation using folate
• IUPAC nomenclature of folate related compounds