Folate Cycle

This page contains educational material about the Folate Cycle. This information is for educational purposes only. Nothing in this text is intended to serve as medical advice. All medical decisions should be made only with the guidance of your own personal medical authority. I am doing my best to get this data up quickly and correctly. If you find errors in this data, please let me know.

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Folate is a water-soluble vitamin that is present in a wide variety of foods, particularly in green leafy vegetables. The term folate is derived from the Latin word folium meaning leaf. Folate, a water-soluble vitamin, is essential for maintaining normal cellular growth, development and general function. This vitamin acts as a cofactor in a number of critical metabolic reactions that include synthesis of precursors of DNA and RNA, metabolism of certain amino acids (e.g., methionine), and other methylation reactions. Folate deficiency leads to a variety of health conditions. More commonly recognized conditions are megaloblastic anemia and neural tube defects.

Folate and Folic Acid are Two Different Things
The folates found in food consist of a mixture of reduced folate polyglutamates. (These are forms the body can utilize easily.) It is found in green vegetables, yeast, egg yolk, liver, and kidney. The reduced forms of the vitamin, particularly the unsubstituted dihydro and tetrahydro forms, are unstable chemically. There is a decrease in folate during harvesting, storage, processing, and preparation. Half or even three-quarters of initial folate activity may be lost during these processes. Thus, natural folates rapidly lose activity in foods over periods of days or weeks and this is one reasons garden fresh food is healthier than food that has been stored. Heat also destroys folate. This is in contrast to the stability of the synthetic form of this vitamin, folic acid. Since folic acid is the more stable of the two forms, manufacturers of food have used it in supplements and fortified foods. In this form the pteridine (2-amino-4-hydroxypteridine) ring is not reduced, rendering it very resistant to chemical oxidation. However, before folic acid can be used by the body, this synthetic form of the vitamin must first be converted to the naturally bioactive form, which occurs via reduction reactions catalyzed by dihydrofolate reductase(DHFR), followed by methylation. Most of the research around conversion of folic acid has been with rodent models or on in-vitro human cell lines which are thought not to give relalistic results for a variety of reasons. Even with these studies there were the following issues: The first step changing folic acid to dihydrofolate is slow and competes with activity further down the chain. Not all of the folic acid is converted. You can end up with what is called unmetabolized folic acid(UMFA). The next step converting dihydrofolate to tetrahydrofolate also utilizes DHFR but the process is faster and this is not usually a bottle-neck area. Even if this was true for humans as well as rodents, we would have to remember that some people have genetic variations that decrease the activity of DHFR. This would create a further issue for these folks. Now although this is still the current acceptable point of view as to what happens to folic acid in the body, the fact is that more recent research (Imran Patanwala, Am J. Clinical Nutrition, 2014) was actually done on humans with a transjugular intrahepatic porto systemic shunt. This study left no doubt in my mind after reading it that it is unlikely that most humans can convert much of the folic acid in their intestinal mucosa to 5-MTHF. Humans appear to have a low enzyme activity of DHFR to biotransform folic acid in the gut mucosa. So, it appears the mucosal cells can methylate folic acid but they are unable to reduce it. It is important to note that the reduction has to happen first before methylation can take place.This means much of the folic acid ends up in the hepatic portal vein as folic acid. So, it ends up in the liver. A recent study showed that the human liver has a low and highly variable DHFR activity. So, in many people the liver will also have trouble transforming the folic acid appropriately. (Bailey et. al., Proc Natl Acad Sci USA, 2009)

Another interesting finding in the research by Imran Patawala is that the synthetic folic acid is not absorbed as well as the natural 5-FormylTHF. Almost two times more foalte from 5-FormylTHF was absorbed across the gut wall than the folic acid. They were not sure if this was truely due to absoprtion differences into the mucosal cells or differences in transporting the folic acid out of the mucosal cells into the portal blood less effectively.

The key message here is that the body receives the natural plant derived and the synthetic form differently and this may present a problem for people ingesting the synthetic form. Since the synthetic form is by law added to many foods in the United States, many people are ingesting the synthetic form. Additionally, as we get older, it is thought that we have more trouble processing folic acid. The fact that the synthetic form is in many conventional foods, and supplements may be an issue for people in general but the elderly even more so. Therefore you will find supplement companies who have taken folic acid out of their products.

For dietary supplements, it is suggested that folic acid could be replaced with natural folate. Hopefully, the issue of folic acid in our food as a fortification agent will be examined and folica acid will no longer be allowed in any food in the future.

This issue becomes further compounded when you realize that unmetabolized folic acid (UMFA) in the blood may be associated with adverse effects. There has not been much research on UMFA, however it has been shown that UMFA is associated with a decrease in natural killer cell (A type of white blood cell) cytotoxicity. This would keep the natural killer cells from killing cancer cells. The theory is that the non-active folic acid is binding to the folate receptors and keeping folate from doing its job. There has been some conjecture that the increased incidence in some cancers such as colorectal cancer has been from the use of folic acid in foods and supplements. Epidemiological research has shown folate in food to be helpful in preventing cancer in the past. This leads me to the following question. Could this relationship to cancer be due to the increased synthetic folic acid or UMFAs associated with folic acid? Could it be that we are taking too much folate/folic acid of any kind? Personally, I think that it is the synthetic folica acid that is the issue. Since it is not being altered into a useful form, this means a foreign body is in our blood that our liver and other cells have to deal with. We need further research to see if this is due to people taking too much folic acid and or folate or if it is a folic acid/UMFA issue. People have noticed the increase in cancer since food fortification with folic acid, but not enough attention is being paid to the UMFA issue.

Addition of a one-carbon units and subsequent reduction steps produce 5-methyltetrahydrofolate (5-MTHF) , which is the main form of folate in the circulation. From the blood, specific carriers or receptors transport 5-MTHF into cells. Only monoglutamate forms can be transported across cell membranes. In the cell, multiple glutamate residues are added, being linked via the γ-carboxyl peptide bond, in a step known as polyglutamation. The incorporation of long polyglutamate chains alters the properties of the molecules such that they cannot be transported through the membrane and so they accumulate in the cells. In addition, enzymes involved in folate metabolism have higher affinities for folate polyglutamates.

The active form of 5-MTHF is the active folate that the body uses in most but not all bodily processes. If there is any problem in the pathway it will not be formed in adequate quantities to keep up with the bodies needs. This can cause everything from fatigue to outright disease processes. Therefore if someone has a single nucleotide polymorphism (SNP) effecting enzymatic action or creation of cofactors necessary for the pathway or effecting transporters or cell membranel receptors for 5-MTHF it is helpful to know this data. Often, dietary or supplement changes can be made to make up for these genetic variations. Of course something as simple as not getting enough dietary B2 in your food could also disrupt an otherwise free flowing folate cycle. Below I have mapped out the folate cycle with the enzymes in purple and cofactors (vitamins) in green.



Folate Cycle

Now to really freak you out, I have a more complicated folate cycle attached to a simple methionine cycle. This shows 5-MTHF donating a methyl group to homocysteine to create methionine. It also shows some more pathways inside the folate cycle.

Note that 5 MTHF is joining up with B12 and the enzyme methionine synthase to turn homocysteine into methionine. This is how 5 MTHFR supports the methylation cycle. Methylation needs this reduced form of folate (5 MTHF) to keep the methionine cycle going. Without it homocysteine will build up and back the cycle up. Also note, SAM is providing a methyl compound to be used as needed and it then SAM becomes SAH when it gives up that methyl compound. This is why the folate cycle is so important to the methionine cycle which is also called the methylation cycle. Some people included the folate cycle as part of the methylation cycle.

More Comprehensive Folate Cycle with Simple Methionine Cycle Attached

folate cycle to methionine

5-methyl tetrahydrofolate(5-MTHF) is what we call "active folate". You will also see it called levomefolic acid, L-methylfolate , and (6S)-5-methyltetrahydrofolate. It is a B vitamin that is the end product of the "Folate Cycle". As you can see the methionine cycle can not function without it. This is why the folate cycle becomes an important part of the methylation cycle. For the folate cycle to function properly it also requires enzymes and cofactors of which many are listed above.

Other Actors in Folate Use by the Body

Three cellular mechanisms for folate transport have been identified: folate receptors (FR), reduced folate carrier (RFC), and the proton-coupled folate transporter (PCFT).

Folate receptor activity involvement: Folate receptors bind folate and reduced folic acid derivatives and mediate delivery of tetrahydrofolate to the interior of cells. It is then converted from monoglutamate to polyglutamate forms. Only monoglutamate forms can be transported across cell membranes. Polyglutamate forms are biologically active enzymatic cofactors required for many folate-dependent processes such as folate-dependent one-carbon metabolism.

Human proteins from this family include folate receptor 1 (adult), folate receptor 2 (fetal), and folate receptor gamma.


What Does Folate Do in the Body

As mentioned above, folate acts as a source of methyl groups for the methylation cycle. It supplies methyl groups for the Queen of the methylators s-adenosyl methionine (SAM or SAMe). SAM acts as a methyl donor to many methyltransferase enzymes. These enzymes are involved in methylating many substrates including lipids, hormones, proteins, DNA etc.

Folic acid is an essential vitamin for a wide spectrum of biochemical reactions. Unlike bacteria and plants, mammals are devoid of folate biosynthesis and thus must obtain this cofactor from exogenous sources. However, one thing that is not usually examined is the fact that humans have bacteria in our gut. It is likely that we make a certain amount of folate in our own intestines. Indeed there is rodent research that found their gut bacteria made folate. Ours probably does too.

Biologically, folate is critical in DNA synthesis and repair, and as cofactors in biological reactions involving folate sources. Folate is involved in the synthesis of thymidylate which is needed for DNA. It also participates in the synthesis of purines needed for DNA, RNA and ATP Additionally, it also participates in the metabolism of the amino acid histidine.

Therefore , folate deficiency may impair the de novo biosynthesis of purines and thymidylate and thereby disrupt DNA and RNA metabolism , homocysteine remethylation , methionine biosynthesis , and subsequent formation of S-adenosylmethionine ( the universal methyl donor ) which in turn may lead to altered methylation reactions.

Folate is regenerated in the folate cycle/methylation cycle but there is quite a bit of catabolism of folate and after it is broken down it is excreted in the urine, bile and even the skin. So the body must get more folate via the diet. Without enough folate intake methylation and DNA/RNA/purine synthesis will suffer. All cells are effected but those dividing the fastest are effected the most. For example, you see the effect in red blood cell production where you get megaloblastic anemia from lack of folate. You also see it in the gut where the gut lining is constantly replacing itself. This can cause digestive problems such as malabsorption.

What causes folate deficiency

Malabsorption problems due to celiac disease or glutlen sensitivity or other food sensitivities can be a causative factor. The fetus needs a lot of folate for growth of those fast dividing cells, so the mom can become folate deficient. Lactating women also loose folate in their milk and need more during lactation. A person can also have genetic variations that can cause them to have trouble making activated forms of folate that are needed. They might be getting enough folate orally, but they might not turn enough of it into 5-10MTHF due to lack of key enzymes such as MTHFR. Luckily folate deficiency can be diagnosed with a blood test and genetic lack of enzymes can also be tested for. Let's take a closer look at the bodies response to folate deficiency.

Bodies Response to Folate Deficiency

The body adapts to folate deficiency in its relation to 1) folate uptake, 2) intracellular folate retention , 3) folate-dependent metabolism , and 4) active folate efflux as follows:

Up - or down regulation of various folate-dependent enzymes like dihydrofolate reductase ( DHFR ) and thymidylate synthase ( TS )
Cellular retention of folates via polyglutamylation by the enzyme folylpoly-gamma-glutamate synthetase ( FPGS )
Over expression of folate influx systems including the reduced folate carrier ( RFC ), folate receptor ( FR ) and the proton-coupled folate transporter ( PCFT)

One of the most common reasons for folate deficiency symtpoms is actually due to an enzyme that is commonly deficient in people. This is the MTHFR enzyme previously mentioned. Variants(mutations) if this enzyme can cause a deficiency in 5,10-MTHF. These variants are called single nucleotide polymorphisms or SNPs.

There are two specific MTHFR enzyme SNPs I would like to tell you about and one of them really disrupts the creation of MTHF. The other one was thought to cause a problem with MTHFR but now seems to add to decreased tetrahydrobiopterin (BH4) activity. These two common and well known SNPs are C677T variant and A1298C variant.

The C677T variant and A1298C variant SNPs are really common
White: European and north American  25-45% have one C677T variant
8-18% have two C677T variants
15-20% have one C677T and One A1298C variant
4-12% have two A1298C variants.

Hispanic –US 42% have one C677T variant
21% have two C677T variants
4-5% have two A1298C variants

Black –US 14% have one C677T variant
1% have two C677T variants
2-4% have two A1298C variants

Asian- Japanese 35% have one C677 Variants
12% have two C677 variants
1-4% have two A1298C variants

Some people think they can simply test homocsysteine levels and if high they have a methylation problem and if normal, they don't. However, it is not that simple. You can have MTHFR variants without having high homocysteine and it can still be a problem.

Lets look closer at these two common variants

MTHFR C677T (A222V, rs1801133)

Wild type = 677CC (natural from generation to generation)

677 denotes the 677th position on dna/enzyme. At the 677th position on the DNA strand for the MTHFR gene there is a switch of  cytosine to thymine.

1 copy= heterozygous = 40% loss of function
2 copies= homozygous = 70% loss of function

People who have a defect in MTHFR 677 are thought to be at risk for dysregulation in these areas:
Cardiovascular issues
Elevated homocysteine
DNA regulation
Glutathione production
Low methylfolate levels

MTHFR A1298C (E429A, rs1801131)

Wild type= 1298AA (natural from generation to generation)

1298 denotes the 1298 position on dna/enzyme. At the 1298th position on the DNA strand for the MTHFR gene
Controversial links – hard to find biochemical reasons for how it is working. Seems to be linked to biopterin. Methyl folate feeds into biopterin – BH4 – With the variant you see lower BH4 (this is what causes most of the issues with A1298C variation), pain, neurological issues, problems making neurotransmitters,  nitric oxide elevations and  peroxynitrate elevations. Should be producing methyl folate ok though although I have seen some research that looks like it might effect it. More will be known as additional research comes fourth.


Health Conditions Related to Inadequate Folate (I will fill this in with the details soon.)

The impaired folate-dependent intracellular metabolism can lead to several key pathologies including, megaloblastic anemia , homocysteinemia , cardiovascular disease , embryonic defects; in particular neural tube defects ( NTDs ) , congenital heart defects , and possibly cancer. A long list of conditions or diseases follow that are thought to be associated with folate deficiency.


Alzheimer's: Folate deficiency induces several Alzheimer pathomechanisms like oxidative stress, Ca(++) influx, accumulation of hyperphosphorylated tau and β-amyloid. There is some research to support this. For example Proceedings of the National Academy of Sciences, found that vitamins B6, B12, and folic acid may help slow the progression of Alzheimer's.



Addictive behaviors



Alcoholic induced pancreatitis is often associated with folate deficiency and is a major cause of acute and chronic pancreatitis. Chronic alcohol feeding of rats (4 wk; 36% of calories from ethanol) led to a significant decrease in folate uptake by freshly isolated primary pancreatic acinar cells compared with cells from pair-fed controls; this effect was associated with a parallel decrease in the level of expression of reduced folate carrier (RFC) and proton-coupled folate transporter (PCFT). These studies reveal that folate uptake by pancreatic acinar cells is via a regulated carrier-mediated process which may involve RFC and PCFT. In addition, chronic alcohol feeding leads to a marked inhibition in folate uptake by pancreatic acinar cells, an effect that is associated with reduction in level of expression of RFC and PCFT.

Anemia - megaloblastic


Autism: A study of low-functioning autistic children showed a link between autism and low cerebral folate levels.They had normal serum folate but low cerebral folate. The researchers found folate receptor antibodies in many of the children. There were no genetic mutations. Stephanie Seneff, who is a researcher who has been studying autism for years has theorized that "irreversible binding of folic acid to the folate receptors could induce an autoimmune response to the receptor-folic acid complex that leads to the development of antibodies to the folate receptors." She is a smart cookie and this sounds plausible to me. In support of ther theory, she notes that mothers with antibodies to human placental folate receptors have been shown to be more likely to have neural tube defects.

Cancer: Convincing evidence links folate deficiency with colorectal cancer incidence. Colorectal cancer incidence is inversely associated with both dietary folate intake and blood cell folate concentrations. Supplementation of folate to prevent colon cancer has had varied results due to folic acid being used in the research rather than active folate. More research is needed with folate, not folic acid.

Folic acid has been shown to increase mammary tumors in rats. Folic acid promoted an increase in weight and volume of the tumors compared to rats not given the folica acid.

How folate deficiency is thought to lead to cancer is by preventing DNA mutations. Folate deficiency affects DNA stability. This happens through two potential pathways. 5,10-Methylenetetrahydrofolate donates a methyl group to uracil, converting it to thymine, which is used for DNA synthesis and repair. If folate is limited, imbalances in the DNA precursor pool occur, and uracil may be misincorporated into DNA. Subsequent misincorporation and repair may lead to double strand breaks, chromosomal damage and cancer. Moreover, folate affects gene expression by regulating cellular S-adenosylmethionine (SAM) levels. 5-Methyltetrahydrofolate serves as methyl donor in the remethylation of homocysteine to methionine, which in turn is converted to SAM. SAM methylates specific cytosines in DNA, and this regulates gene transcription. As a consequence of folate deficiency, cellular SAM is depleted, which in turn induces DNA hypomethylation and potentially induces proto-oncogene expression leading to cancer. Data from several model systems supporting these mechanisms are reviewed here. There is convincing evidence that folate modulates both DNA synthesis and repair and DNA hypomethylation with altered gene expression in vitro.

Cardiovascular risk

Cervical dysplasia

Chemical sensitivity

Chronic fatigue syndrome

Chronic viral infection

Chronic pain

Cleft palette

Colon Effects: Chronic alchohol ingestion appears to effect folate transport across the colon membranes. Chronic alcoholism decreased the proton-coupled folate transporter (PCFT) and the reduced folate carrier (RFC) protein levels in the CAM LR in accordance with the decreased synthesis. The researchers proposed that downregulation in the expression of the PCFT and the RFC in colon results in reduced levels of these transporters in colon apical membrane lipid rafts as a mechanism of folate malabsorption during chronic alcoholism. (Wani and Kaur 2011)

Congenital heart defects

Depression: Substantial evidence from population, case-control and cross-sectional studies suggest poor dietary folate intake and correspondingly low folate status is associated with depression after controlling for confounding factors (Gilbody et al 2007). This evidence comes mainly from Western countries but in a cross-sectional study of the Japanese population aged 21-67 years researchers looked at associations between folate, other B vitamin and essential fatty acid (EFA) intakes and found only low folate to be associated with increased prevalence of depressive symptoms, at least in men. In a recent cross-sectional study of older Chinese serum folate concentrations were lower in individuals with depression compared to those without (Ng et al 2009); a linear relationship between serum folate concentration and depressive symptoms independent of homocysteine levels suggests the role of folate as a cofactor in neurotransmitter synthesis is an important mediator in depression. However, a large population study found it was elevated homocysteine (≥15.0 μmol/L or 2.02 mg/dL) along with a single nucleotide polymorphism (SNP) associated with impaired methylation that were significantly related to depression rather than folate status alone (Bjelland et al 2003). Measurement of plasma rather than serum folate concentrations in the latter study may account for the contrary findings but in practice the biochemical mechanisms are likely to be less important than therapeutic outcomes. Given the quantity and quality of the evidence base linking low folate intakes and status to depression it would seem remiss of Nutritional Therapists not to recommend consumption of a diet high in folate rich foods including legumes, nuts and seeds, okra and asparagus (Whitney et al 2002:327).

Folate is converted to monoglutamate entities by the enzyme alpha-L-glutamyl transferase in the intestinal wall as they are absorbed. Once absorbed, monoglutamate entities are converted to methylenetetrahydrofolate (MTHF), the fat soluble form of folate that passes into the brain and is utilized by trimonoamine neurons to facilitate neurotransmitter synthesis or dopamine, epinephrine and norepinephrine. Normally, ingesting folate from dihydrofolate in the diet will result in adequate delivery of MTHF levels to the brain, especially in those individuals with the more efficient methylation genotype (C677C) producing up to 100% of the enzyme methylene tetrahydrofolate reductase and who do not have depression.

In patients with methylation deficiencies, the level of MTHF produced is limited, therefore limiting dopamine production. Thus, administration of folinic acid or MTHF, has significant advantages over administration of folic acid as a trimonoamine modulator to depressed or anxious patients or depressed patients who do not respond adequately to their antidepressant treatment. These patients may not be folate deficient on standard blood work.


Down’s syndrome

Drug sensitivities

Elevated histamine

Elevated cobalamin


Immune deficiency



Neural tube defects: Folate deficiency during the first trimester is a significant risk factor for neural tube defects.

Neurological disorders


Multiple sclerosis

Pancreatic cancer: All mammalian cells, including those of the pancreatic acini, are unable to synthesize folate and thus must obtain the vitamin from the extracellular environment via transport across the plasma membrane. The pancreas maintains the second highest level of folate after the liver, and folate is essential for its normal exocrine function and health. Studies have suggested that disturbances in the folate-dependent methyl group metabolism in the pancreas contribute to the pathogenesis of several pancreatic disorders and that an inverse relationship exists between serum folate level and the risk of human pancreatic cancer.



Pulmonary embolism

Recurrent miscarriages


Spina bifida

Supplement sensitivities

Thyroid dysfunction


Drug or Supplement Interactionswith Folate absorption of Activity

Folic acid inhibits dihydrofolate reduction to tetrahydrofolate competitively. (Zakrzewski, 1960)

Methotrexate inhibits dihydrofolate reductase which is necessary to convert folic acid to dihydrofolate and also necessary to convert dihydrofolate to tetrahydrofolate.

Antacids should be avoided because they deplete B12. Nitrous Oxide inactivates MS (methionine synthase - b12 dependent enzyme changes homocysteine into methionine. So introus oxide needs to be avoided. This can be dangerous, and even fatal. Oral contraceptives deplete folate. Metformin decreases B12 absorption. Bactrim reduces the function of important enzymes.

Folate deficiency may cause:

Gray hair
Mouth sores (ulcers)
Poor growth
Swollen tongue

Forms of folate Supplements

Folinic acid = a reduced form with the chemical name of 5-formyl tetrahydrofolate.

L-5 methyl tetrahydrofolate (5-MTHF) = fully active folate. The end product of the folate cycle. This will be in short supply if a person does not have adequate B2(riboflavin) or is lacking enough MTHFR enzyme.

If you found this information helpful, I would appreciate your support in keeping the site going. If you would like to donate to my work, I thank you in advance and send you my deep felt gratitude.

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