Lab result explainedVitamins and mineralsLast updated November 8, 2026

Folate blood test: what low and high folate levels mean

Folate (serum and red cell folate) (Folate) · Folate (usually ordered with vitamin B12 and a CBC) · reported in ng/mL (some labs report nmol/L — multiply ng/mL by 2.266)

Folate is vitamin B9, the nutrient your cells need to copy DNA and make new red blood cells, and a folate blood test measures how much of it you have. There are two versions: serum folate, which reflects what you have eaten over the past few days, and red cell (RBC) folate, which reflects your stores over the past three to four months. On most US reports a serum folate above about 4 ng/mL is normal, below 3 ng/mL is deficient, and an RBC folate between roughly 140 and 628 ng/mL is normal.

Since 1998, when the US began adding folic acid to enriched flour, bread, pasta and rice, outright folate deficiency has become rare: under 1 percent of the population, down from around 16 percent before fortification. Today a low folate usually points to something specific: heavy alcohol use, a very poor diet, a bowel condition that blocks absorption such as celiac or Crohn's disease, a medicine that interferes with folate (methotrexate, phenytoin, sulfasalazine, trimethoprim), or a higher demand from pregnancy or rapid cell turnover.

The more common surprise on a modern report is a high folate, usually reported as above 20 ng/mL. Most of the time this simply reflects a supplement or fortified foods and does not matter. It becomes important in one situation: when folate is high and vitamin B12 is low. Folic acid can correct the anemia of B12 deficiency while nerve damage from the B12 shortage continues, and in older adults the high-folate, low-B12 combination has been linked to worse anemia and poorer cognition than low B12 alone.

Folate at a glance

  • What it is: vitamin B9, needed for DNA synthesis and red cell production; stored in the liver for only 3 to 4 months, so levels fall quickly on a poor diet.
  • Normal serum folate: above about 4 ng/mL on most US reports (labs quote 3–17 or above 5.4 ng/mL); 3–4 ng/mL is borderline and below 3 ng/mL is deficient.
  • Normal red cell folate: roughly 140–628 ng/mL; below 140 ng/mL confirms long-standing deficiency. Red cell folate is less affected by what you ate yesterday.
  • Low folate causes large red cells (MCV over 100 fL) and anemia, raises homocysteine, and in early pregnancy increases the risk of neural tube defects.
  • High folate (above 20 ng/mL) nearly always means supplements or fortified food and is harmless on its own; it matters only when B12 is also low, which it can mask.
  • Next step: check B12 at the same time, review alcohol, diet and medicines; folic acid 400 to 1,000 mcg daily corrects deficiency within weeks once the cause is addressed.

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What Folate measures

Serum folate measures the folate circulating in the liquid part of your blood, mostly as 5-methyltetrahydrofolate, the form cells use. Because it responds to intake within a day or two, it is a good test for current supply and a poor test for stores: a single folate-rich meal or a supplement taken the morning of the test can push a genuinely depleted person into the normal range, and a few days of poor eating or heavy drinking can push a well-stocked person below it. For this reason the test is ideally drawn fasting and before any supplement.

Red cell folate measures the folate locked inside red blood cells. Folate is taken up while the cell is being built in the marrow and stays there for the cell's 120-day life, so the result averages your folate status over the preceding three to four months, much as A1C does for glucose. It is the better test when you need to know about stores, for example in suspected malabsorption or when serum folate is borderline, but it is more expensive, less standardised between labs, and can read falsely low in B12 deficiency, because B12 is needed to trap folate inside cells.

Both tests are run by immunoassay, and reference intervals differ between manufacturers. Results may be reported in ng/mL or in nmol/L (multiply ng/mL by 2.266). Homocysteine is the functional check: it rises when folate is short, falling within two weeks of replacement, though it also rises with B12 or B6 deficiency, kidney disease and hypothyroidism. Hemolysis of the sample falsely raises serum folate, since red cells contain 20 to 30 times the serum concentration.

Normal range for Folate

Reference ranges vary between labs and by age, sex and pregnancy. Use the range printed on your own report.

GroupTypical range (ng/mL (some labs report nmol/L — multiply ng/mL by 2.266))Notes
Serum folate, deficientBelow 3 ng/mLMegaloblastic changes are likely; this is also the WHO cut-off (below 10 nmol/L) for population surveys.
Serum folate, borderline3–4 ng/mL (some labs to 5.9)Indeterminate; red cell folate or homocysteine helps decide. A level this low in early pregnancy is a reason to supplement at once.
Serum folate, normalAbove about 4 ng/mL (typical intervals 3–17, 4.6–18.7 or above 5.4 ng/mL)Labs differ; use the interval printed on your report. Most US adults eating fortified grains run 10 to 20 ng/mL.
Serum folate, highAbove 20–24 ng/mL (often reported as 'greater than 20')Almost always from folic acid supplements or heavily fortified foods. Harmless alone; check B12.
Red cell folate, deficientBelow 140 ng/mL (below about 305 nmol/L)Confirms depletion of stores over the previous 3 to 4 months.
Red cell folate, normalAbout 140–628 ng/mLIntervals vary widely between labs. For neural tube defect prevention, an RBC folate above about 400 ng/mL (906 nmol/L) is the WHO target in women who may become pregnant.
PregnancySerum folate falls by about a third by the third trimesterDilution and fetal demand; the RDA rises from 400 to 600 mcg DFE a day.
Daily requirement (RDA)400 mcg DFE adults; 600 mcg pregnancy; 500 mcg breastfeeding; upper limit 1,000 mcg from folic acidDFE = dietary folate equivalents; folic acid from supplements counts for 1.7 times its weight because it is better absorbed than food folate.

High folate

A folate above the lab's upper limit, usually reported as above 20 or 24 ng/mL, almost always means you are getting folic acid from a supplement, a prenatal vitamin, a B-complex or a diet heavy in fortified cereals and breads. Folate is water-soluble and the excess is cleared in urine; there is no toxicity from food folate and no action is needed for a high result in someone whose B12 is normal. It can also appear after a recent folate-rich meal if the test was not fasting, and in a hemolysed sample.

The one combination that matters is high folate with low B12. Folic acid repairs the DNA-synthesis defect that both deficiencies cause in the bone marrow, so it corrects the anemia and shrinks the MCV back to normal, removing the warning signs while B12 deficiency continues to damage nerves. In the US NHANES survey of adults over 60, those with low B12 and high folate were around two to five times more likely to have anemia and cognitive impairment than those with low B12 and normal folate, and some studies find the combination worsens the biochemical signs of B12 deficiency itself. This is why the two are always measured together and why B12 is checked before anyone starts folic acid above 400 mcg.

Doses above the 1,000 mcg upper limit also leave unmetabolised folic acid circulating in the blood, because the liver enzyme that converts it is easily saturated at intakes above about 200 to 400 mcg at one time. Unmetabolised folic acid is detectable in most Americans and its long-term meaning is uncertain: it has been linked in some studies to lower natural killer cell activity and, in one trial of 1,000 mcg a day for people with a history of colorectal polyps, to a higher rate of advanced polyps rather than a lower one. These findings are not settled, but they are the reason high-dose folic acid is reserved for people with a defined need.

Common causes

  1. Folic acid supplements, prenatal vitamins and B-complex

    A standard 400 mcg supplement raises serum folate into the upper teens; 800 to 1,000 mcg or more commonly produces values above the 20 ng/mL reporting limit.

  2. Fortified foods

    Enriched flour products, breakfast cereals (some carry 400 mcg a serving), energy drinks and meal-replacement shakes contribute folic acid with every serving; heavy cereal eaters often test high.

  3. Recent folate-rich meal or non-fasting sample

    Serum folate responds within hours to intake; a large salad, lentils or liver before the draw can lift the result several ng/mL.

  4. Vitamin B12 deficiency

    Without B12, folate cannot be converted to the form cells trap, so it accumulates in serum as methylfolate while red cell folate falls; a high serum folate with a low RBC folate is a classic B12-deficiency pattern.

  5. Small intestinal bacterial overgrowth

    Bacteria in the small bowel synthesise folate, so people with SIBO can show a high folate alongside a low B12, which the same bacteria consume.

  6. Hemolysed sample

    Red cells contain 20 to 30 times the folate concentration of serum, so a difficult draw that breaks red cells falsely raises the serum result.

  7. Liver disease

    Acute liver injury releases stored folate; chronic liver disease more often lowers it, so the direction depends on the stage.

Symptoms that can go with it

  • None; a high folate from supplements or diet causes no symptoms
  • If B12 is also low: numbness, tingling, unsteady walking, memory problems or low mood, which the folate has not corrected
  • High-dose folic acid (above 1,000 mcg) occasionally causes nausea, bloating, a bitter taste, sleep disturbance or irritability
  • Very rarely, allergic reactions to folic acid tablets with rash or itching
  • A high serum folate with a low red cell folate and a raised MCV points to B12 deficiency rather than folate excess

Low folate

A serum folate below 3 ng/mL, or a red cell folate below about 140 ng/mL, means your supply of folate is not keeping up with demand. Because the body stores only three to four months' worth, folate deficiency develops faster than B12 deficiency and shows up first in the fastest-dividing cells: the bone marrow, producing large red cells (MCV over 100 fL), a raised RDW and eventually anemia, and the lining of the mouth and gut, producing a sore tongue and mouth ulcers. Homocysteine rises, and in early pregnancy the fetus's developing spinal cord is at risk.

In the US, with grain fortification in place, the question behind a low result is almost always why. Heavy alcohol use is the leading cause: alcohol both displaces food and blocks folate absorption and recycling. Malabsorption from celiac disease, Crohn's disease, bariatric surgery or chronic diarrhoea is next, followed by medicines that antagonise folate (methotrexate, phenytoin, carbamazepine, valproate, sulfasalazine, trimethoprim) and states of high demand such as pregnancy, breastfeeding, hemolytic anemias including sickle cell disease, widespread psoriasis and dialysis. A diet of almost no vegetables, fruit, legumes or fortified grains, common in frailty, eating disorders and food insecurity, still causes deficiency.

Because B12 deficiency produces an identical blood picture and can itself lower red cell folate, B12 is always checked before or alongside folate, and if there is any doubt both are replaced together. Treating with folic acid alone when B12 is also low will correct the anemia and leave the nerves unprotected. With the cause addressed, folic acid 400 to 1,000 mcg a day (prescription doses of 1 to 5 mg are used for malabsorption and in pregnancy with a prior neural tube defect) restores levels within weeks: reticulocytes rise in a week, hemoglobin normalises in about two months.

Common causes

  1. Alcohol use disorder

    The commonest cause in fortified countries. Alcohol reduces intake, blocks absorption in the jejunum, impairs the liver's release of folate into bile and increases urinary loss; folate falls within days of heavy drinking and MCV is often raised from the alcohol itself.

  2. Poor diet

    Few vegetables, fruit, legumes or enriched grains, as seen in frail older adults, eating disorders, restrictive fad diets and food insecurity. Overcooking matters too: boiling leaches 50 to 80 percent of folate out of vegetables.

  3. Celiac disease, Crohn's disease and other malabsorption

    Folate is absorbed in the first part of the small bowel (the duodenum and jejunum), exactly where celiac disease does its damage; a low folate with low iron is a classic celiac combination. Tropical sprue, extensive Crohn's and chronic diarrhoea also lower it.

  4. Methotrexate, trimethoprim and other folate antagonists

    Methotrexate (for rheumatoid arthritis, psoriasis, cancer) and trimethoprim (in co-trimoxazole) block the enzyme that activates folate; pyrimethamine does the same. Folic acid 1 mg daily is routinely co-prescribed with methotrexate to prevent deficiency without blunting its effect.

  5. Anticonvulsants and sulfasalazine

    Phenytoin, carbamazepine, phenobarbital, primidone and valproate lower folate by 20 to 50 percent through faster breakdown and reduced absorption; sulfasalazine blocks absorption directly. Metformin and oral contraceptives have a smaller effect.

  6. Pregnancy and breastfeeding

    Demand rises by 50 percent to supply the growing fetus and placenta; without supplementation, serum folate falls steadily through pregnancy, and deficiency in the first 28 days raises neural tube defect risk.

  7. Rapid cell turnover

    Hemolytic anemias (sickle cell disease, thalassemia, hereditary spherocytosis), extensive psoriasis or exfoliative skin disease, and some leukemias consume folate quickly; sickle cell disease patients are commonly prescribed daily folic acid.

  8. Dialysis

    Folate is water-soluble and removed by hemodialysis; most dialysis patients receive a daily supplement.

  9. Gastric bypass and sleeve gastrectomy

    Reduced intake and bypass of the duodenum lower folate in up to a third of patients without supplements; lifelong multivitamins are standard.

  10. MTHFR gene variants

    People who carry two copies of the common C677T variant (about 10 percent of white and Hispanic Americans) have modestly lower folate and higher homocysteine, particularly when intake is low. Routine MTHFR testing is not recommended by professional bodies, because adequate folate intake corrects the effect and the standard dose of folic acid works.

Symptoms that can go with it

  • Fatigue, weakness, breathlessness on exertion and pale skin from anemia
  • A sore, smooth, red tongue, mouth ulcers and cracks at the corners of the mouth
  • Loss of appetite, weight loss and diarrhoea
  • Irritability, low mood, poor concentration and forgetfulness
  • Headache and palpitations as the anemia deepens
  • Unlike B12 deficiency, folate deficiency does not usually cause numbness, tingling or unsteadiness; if those are present, B12 needs checking
  • In pregnancy, no symptoms in the mother, but a higher risk of neural tube defects, placental abruption and low birth weight

Read it alongside

  • Vitamin B12 — always measured together; the deficiencies look alike on a blood count, and folic acid alone can mask B12 deficiency while nerve damage continues.
  • MCV and RDW — both deficiencies enlarge red cells (MCV over 100 fL) and widen the RDW; a normal MCV with coexisting iron deficiency does not rule folate deficiency out.
  • Hemoglobin and reticulocyte count — show whether anemia has developed and, after treatment starts, whether the marrow is responding (reticulocytes peak around day 7).
  • Homocysteine — rises with folate deficiency and falls within two weeks of replacement; also a check that the result is functionally real.
  • Methylmalonic acid — normal in pure folate deficiency and raised in B12 deficiency, so it separates the two when both vitamins are borderline.
  • Ferritin and celiac antibodies (tissue transglutaminase IgA) — low folate with low iron is a strong pointer to celiac disease or another duodenal problem.
  • Liver enzymes (GGT, AST) — support a picture of alcohol-related deficiency when folate is low and MCV is high.
  • Red cell folate — ordered when serum folate is borderline or a recent meal or supplement may have distorted it; reflects the previous 3 to 4 months.

What usually happens next

  1. A low folate is paired with a B12 result before treatment; if B12 is low or borderline, both are replaced, with B12 started first or at the same time.
  2. Expect a CBC with MCV and reticulocytes, homocysteine, ferritin, and often celiac antibodies and liver tests; a review of alcohol intake, diet and medicines (methotrexate, anticonvulsants, sulfasalazine, trimethoprim) usually finds the cause.
  3. Folic acid 400 to 1,000 mcg a day for about four months rebuilds stores; prescription doses of 1 to 5 mg are used for malabsorption, on dialysis, with hemolytic anemia and in pregnancy after a previous neural tube defect. Methylfolate is an alternative that works equally well at equivalent doses.
  4. Recheck a CBC and folate after 8 to 12 weeks; hemoglobin should be normal and MCV returning to normal. If anemia persists, iron deficiency, B12 deficiency, hypothyroidism or a marrow problem is looked for.
  5. If you could become pregnant, the standard advice regardless of your result is 400 mcg of folic acid a day starting at least a month before conception; a low folate makes this more pressing.
  6. For a high folate with a normal B12, no action is needed; if you take more than 1,000 mcg a day without a specific reason, discuss whether the dose is still needed.

Diet, lifestyle and natural levers with evidence

What can move Folate once the cause is known. Nothing here replaces finding the cause.

Folate-rich foods

Strong evidence

Cooked lentils (about 360 mcg a cup), chickpeas and black beans (250 to 280 mcg), spinach (260 mcg a cup cooked), asparagus (270 mcg a cup), avocado (120 mcg each), broccoli, romaine, oranges and beef liver (210 mcg per 3 oz) are the richest natural sources, and enriched bread, pasta, rice and breakfast cereals supply 50 to 400 mcg a serving of folic acid. Controlled feeding studies show that raising intake to 400 mcg DFE a day normalises serum and red cell folate within 8 to 12 weeks and lowers homocysteine by 10 to 20 percent in people who started low. Steaming, microwaving or eating vegetables raw preserves folate; boiling and discarding the water removes up to half or more.

Folic acid or methylfolate supplement (400–1,000 mcg a day)

Strong evidence

Folic acid is about 85 percent absorbed from a supplement against roughly 50 percent for food folate, and 400 mcg a day restores levels in most people with dietary deficiency within a few weeks. The Medical Research Council trial in 1991 found 4 mg a day cut the recurrence of neural tube defects by 72 percent, and population fortification has reduced neural tube defects by about 28 percent in the US. The US Preventive Services Task Force recommends 400 to 800 mcg daily for anyone planning or able to become pregnant. 5-methyltetrahydrofolate (methylfolate) raises folate status as effectively as folic acid in head-to-head trials and does not produce unmetabolised folic acid, though its advantage for people with MTHFR variants is unproven.

Have B12 checked before taking more than 400 mcg a day: folic acid corrects the anemia of B12 deficiency and can let nerve damage progress unnoticed. Keep total folic acid under the 1,000 mcg upper limit unless prescribed. Folic acid can lower blood levels of phenytoin and some other anticonvulsants, so people on them should discuss the dose.

Reducing alcohol

Moderate evidence

Alcohol is the leading cause of folate deficiency in fortified countries, acting on intake, absorption, liver handling and urinary loss at once. In people with alcohol use disorder, folate and MCV improve measurably within 2 to 4 weeks of abstinence when diet is adequate, and observational studies show each additional daily drink is associated with lower serum folate and higher homocysteine. Keeping within one drink a day for women and two for men limits the effect.

Diagnosing and treating celiac disease

Moderate evidence

Folate deficiency is present in 20 to 40 percent of newly diagnosed adults with celiac disease, and a gluten-free diet restores absorption as the duodenal lining heals, with folate, iron and zinc typically normalising within 6 to 12 months in follow-up studies. Anyone with a low folate and low iron without an obvious dietary or alcohol explanation should be tested with tissue transglutaminase IgA (while still eating gluten).

Folic acid alongside methotrexate

Strong evidence

A Cochrane review of six trials in rheumatoid arthritis found folic acid (usually 1 mg daily or 5 mg weekly) cut methotrexate-related nausea and abdominal pain by about 26 percent, abnormal liver enzymes by 77 percent and treatment discontinuation by 61 percent, with no loss of methotrexate's effect on the arthritis. It also prevents the macrocytosis and low folate methotrexate otherwise causes.

Timing and dose are set by the prescriber; folic acid is not taken on the same day as methotrexate in some regimens and never replaces the folinic acid used for methotrexate overdose.

Vitamin C with meals

Preliminary evidence

Vitamin C protects food folate from oxidation during digestion and may modestly improve its absorption; small feeding studies show higher serum folate responses when folate-rich foods are eaten with vitamin C-rich foods, and people with low vitamin C status tend to have lower folate. The effect is small compared with eating more folate, and it has not been tested as a treatment for deficiency.

When to see a clinician promptly

  • A low folate with any numbness, tingling, unsteadiness or memory change, which points to B12 deficiency as well and needs B12 treatment before or alongside folic acid.
  • Severe anemia (hemoglobin below about 8 g/dL) with breathlessness, chest pain, palpitations or fainting: same-day assessment.
  • A low folate in early pregnancy or when trying to conceive, since the neural tube closes by day 28 and supplementation should start at once.
  • Low folate with weight loss, chronic diarrhoea, greasy stools or abdominal pain, which suggests celiac disease, Crohn's disease or another malabsorption problem.
  • Low folate alongside heavy drinking, to address the alcohol as well as the vitamin; thiamine deficiency often accompanies it and is dangerous if missed.
  • A persistently low folate despite supplements, which raises the question of malabsorption, a medicine interaction or an increased-turnover condition that needs its own treatment.

Frequently asked questions

What is a normal folate level?

Most US labs regard a serum folate above about 4 ng/mL as normal, with deficiency below 3 ng/mL and 3 to 4 borderline; typical reference intervals are 3–17, 4.6–18.7 or 'above 5.4' ng/mL, so check the interval on your report. Red cell folate is normal between roughly 140 and 628 ng/mL. Most Americans eating fortified grains run 10 to 20 ng/mL, and values above 20 are common in anyone taking a supplement.

What are the symptoms of folic acid deficiency?

Fatigue, breathlessness and pallor from anemia; a sore, smooth red tongue, mouth ulcers and cracked lips; poor appetite, diarrhoea and weight loss; and irritability, low mood and poor concentration. Folate deficiency does not usually cause numbness, tingling or unsteadiness; if those are present, vitamin B12 deficiency is the more likely cause and must be checked, because folic acid alone will not protect the nerves.

What is the difference between serum folate and red cell folate?

Serum folate measures what is in your blood plasma right now and changes within a day or two of eating or taking a supplement, so it reflects recent intake. Red cell folate measures folate trapped inside red cells when they were made and averages your status over the previous three to four months, like A1C does for sugar. Serum folate is cheaper and usually sufficient; red cell folate is used when the serum result is borderline, a recent meal or tablet may have distorted it, or long-term stores matter, such as in pregnancy planning.

Is high folate bad?

On its own, no. Folate above 20 ng/mL almost always reflects supplements or fortified food and causes no harm; there is no toxicity from food folate. It matters when vitamin B12 is also low, because folic acid corrects the anemia of B12 deficiency while nerve damage continues, and in older adults the high-folate, low-B12 combination is linked to worse anemia and cognition. Taking more than the 1,000 mcg daily upper limit of folic acid without a specific reason is not advised, since the long-term effects of unmetabolised folic acid are uncertain.

Why is my folate high and B12 low?

Three reasons are common. Taking a multivitamin or eating a lot of fortified cereal raises folate while a separate absorption problem, such as atrophic gastritis, metformin or acid suppressants, lowers B12. B12 deficiency itself traps folate in the blood because cells cannot convert it to the storable form. And small intestinal bacterial overgrowth produces folate while consuming B12. Whatever the reason, the B12 needs treating, and folic acid should not be taken alone until it is.

How long does it take to correct folate deficiency?

Serum folate rises within days of starting a supplement or improving your diet. New red cells (reticulocytes) increase within a week, hemoglobin returns to normal in about 8 weeks and the MCV in 2 to 3 months. Stores take about 4 months of 400 to 1,000 mcg a day to rebuild fully, and longer if alcohol, malabsorption or a folate-blocking medicine continues.

Does folic acid help with MTHFR?

Yes. People with two copies of the MTHFR C677T variant convert folate to its active form about 30 percent less efficiently, which shows up as slightly lower folate and higher homocysteine when intake is low. Trials show that standard folic acid, at ordinary doses, corrects both, and methylfolate works equally well without clearly working better. The American College of Medical Genetics and the American College of Obstetricians and Gynecologists do not recommend routine MTHFR testing, because the result does not change the advice: 400 mcg a day, or 600 mcg in pregnancy.

Can you have folate deficiency with a normal MCV?

Yes. Folate deficiency enlarges red cells, but if iron deficiency or thalassemia trait is also present, which shrinks them, the MCV can land in the normal range while the RDW is wide and the blood film shows a mix of large and small cells. About a quarter of people with low folate have a normal MCV. The folate level, not the cell size, makes the diagnosis.

References

  1. Folic acid test. MedlinePlus, US National Library of Medicine (2023)View source
  2. Folate: fact sheet for health professionals. National Institutes of Health, Office of Dietary Supplements (2022)View source
  3. Folate deficiency. Merck Manual Professional Version (2024)
  4. Devalia V, Hamilton MS, Molloy AM; British Committee for Standards in Haematology. Guidelines for the diagnosis and treatment of cobalamin and folate disorders. British Journal of Haematology (2014)
  5. Bailey LB, Stover PJ, McNulty H, et al.. Biomarkers of nutrition for development: folate review. Journal of Nutrition (2015)
  6. Pfeiffer CM, Sternberg MR, Zhang M, et al.. Folate status in the US population 20 y after the introduction of folic acid fortification. American Journal of Clinical Nutrition (2019)
  7. Morris MS, Jacques PF, Rosenberg IH, Selhub J. Folate and vitamin B-12 status in relation to anemia, macrocytosis, and cognitive impairment in older Americans in the age of folic acid fortification. American Journal of Clinical Nutrition (2007)
  8. MRC Vitamin Study Research Group. Prevention of neural tube defects: results of the Medical Research Council Vitamin Study. Lancet (1991)
  9. US Preventive Services Task Force. Folic acid supplementation for the prevention of neural tube defects: US Preventive Services Task Force reaffirmation recommendation statement. JAMA (2023)
  10. Cole BF, Baron JA, Sandler RS, et al.. Folic acid for the prevention of colorectal adenomas: a randomized clinical trial. JAMA (2007)
  11. Shea B, Swinden MV, Tanjong Ghogomu E, et al.. Folic acid and folinic acid for reducing side effects in patients receiving methotrexate for rheumatoid arthritis. Cochrane Database of Systematic Reviews (2013)
  12. Green R, Allen LH, Bjørke-Monsen AL, et al.. Vitamin B12 deficiency. Nature Reviews Disease Primers (2017)

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This page is educational and is not medical advice or a diagnosis. Lab results have to be interpreted together with your history, symptoms and other results by a clinician who knows you. Do not start or stop a supplement to change a lab value before the cause is known.