Folate Deficiency Symptoms: How It Differs From B12, and the Test

Folate deficiency shows as tiredness and weakness, breathlessness, a pale complexion, a sore red tongue and mouth ulcers, irritability, poor concentration and low mood, with sometimes diarrhoea, loss of appetite and a reduced sense of taste; it looks almost identical to vitamin B12 deficiency because both block the making of red blood cells in the same way.¹ Two things usually tell them apart. Folate deficiency rarely causes the pins and needles, numbness and unsteadiness of B12 deficiency, and it develops in months rather than years, because the body holds only a few months' folate against several years' B12. The commonest cause in the UK is simply not eating enough green vegetables, pulses and fortified foods, followed by heavy drinking, pregnancy, gut disease and a handful of medicines.^{1, 2} A blood test settles it, and the one rule that matters is to have B12 checked at the same time, because folic acid taken for a folate deficiency can hide a B12 deficiency while nerve damage goes on.³

• Symptoms: tiredness, breathlessness, pallor, sore red tongue, mouth ulcers, irritability, low mood, poor concentration, diarrhoea, poor appetite
• Not usually: pins and needles, numbness, unsteadiness, which point to B12
• Causes: low intake of greens, pulses and fortified foods; alcohol; pregnancy; coeliac and Crohn's disease; methotrexate, some anti-epileptics, sulfasalazine
• Test: serum folate with B12 and a full blood count; below about 3 micrograms per litre is deficient
• Treatment: folic acid 5 mg a day for about four months, prescribed, after B12 is checked

What folate does and why its lack shows quickly

Folate, vitamin B9, is needed wherever cells divide: in bone marrow making red blood cells, in the gut lining, in an embryo. It works with vitamin B12 to supply the building blocks of DNA, so a shortage of either produces the same large, fragile, scarce red blood cells, megaloblastic anaemia, and the same tiredness and breathlessness.¹ The body stores folate in the liver, but only enough for two to four months, so a diet that drops vegetables, or a demand that rises as in pregnancy, shows in a season. B12 stores last years, which is one reason the two deficiencies behave differently. Folate contributes to normal blood formation, normal psychological function, normal immune function, the reduction of tiredness and fatigue and maternal tissue growth in pregnancy; those are its authorised roles and they match the symptoms of running short. What folic acid does for a woman covers the pregnancy side.

The symptoms, and the first two people notice

The first two are almost always tiredness and breathlessness: a flat fatigue that sleep does not fix and finding stairs harder than they were, both from anaemia. Then pallor, sometimes a racing heart, headaches and feeling faint. The mouth follows: a smooth, sore, red tongue, mouth ulcers and a dulled sense of taste. Appetite falls, weight may drop, and diarrhoea is more common than with B12 deficiency because the gut lining itself divides fast and suffers. Mood and mind: irritability, poor concentration, forgetfulness and low mood, which in older adults can be marked.^{1, 2} Severe deficiency in pregnancy raises the risk of neural tube defects in the baby, which is the reason for the 400 microgram advice. Nerve symptoms, if present, should prompt a hard look at B12.

Folate or B12 deficiency: how to tell

You cannot reliably tell from symptoms, which is why both are tested together. The pointers: pins and needles, numbness, unsteadiness, blurred vision and memory change favour B12; diarrhoea and a very poor diet favour folate; a vegan diet, age over 65, metformin or acid suppressants favour B12; heavy drinking, pregnancy, coeliac disease and the medicines below favour folate; and both are common in people with eating disorders or restrictive diets. Many people are short of both. The signs of B12 deficiency sets out the other half.

What causes folate deficiency?

Diet. The commonest cause: too few green vegetables, pulses, oranges, wholegrains and fortified cereals, and overcooking what there is, since folate leaches into water and breaks down with heat. Older adults eating little, people on very restrictive diets and heavy drinkers who eat poorly are the typical cases.

Alcohol. Reduces folate absorption and increases its loss, on top of displacing food.

Pregnancy and breastfeeding. Demand rises sharply; the 400 microgram supplement exists for this reason, and women carrying twins or with closely spaced pregnancies are at higher risk.

Gut conditions. Coeliac disease, Crohn's disease and bowel surgery reduce absorption; folate deficiency is sometimes the clue that leads to a coeliac diagnosis.

Medicines. Methotrexate, used for arthritis, psoriasis and Crohn's, works by blocking folate and is prescribed with folic acid for that reason; some anti-epileptics (phenytoin, carbamazepine, valproate), sulfasalazine and trimethoprim lower folate too.² Prescribers manage this; do not add folic acid to these without asking.

Higher turnover. Conditions where cells divide fast, such as sickle cell disease and some skin and blood disorders, use more folate.

The blood test

Serum folate, with a full blood count, B12 and usually ferritin. A serum folate below about 3 micrograms per litre is deficient; red cell folate is sometimes used as a longer-term measure.¹ Serum folate rises quickly after eating folate-rich food or taking folic acid, so a test taken after a week of effort can look normal when stores are not; tell the GP what you have been eating or taking. If B12 is also low or borderline, it is treated first or at the same time, never left while folic acid is started alone.³

Treatment and recovery

Dietary deficiency is treated with folic acid 5 mg a day for about four months, on prescription, alongside fixing the diet; the dose then drops or stops unless the cause continues.¹ Energy improves within a couple of weeks, the blood count recovers over four to eight weeks, mouth symptoms settle in a few weeks, and mood and concentration follow. Where a medicine or a gut condition is the cause, folic acid continues as long as the cause does. The UK guidance level for folic acid from supplements without prescription is 1 mg a day, and the reason is exactly the B12 rule: higher doses can correct the anaemia of an undiagnosed B12 deficiency while nerve damage continues.³

Preventing it

The adult reference intake is 200 micrograms a day, met by a diet that includes green vegetables most days, pulses a few times a week, oranges or orange juice, wholegrains and fortified breakfast cereals; foods high in folate has the UK portions. Steam or microwave vegetables rather than boiling them. Drink within the low-risk guidelines. Take 400 micrograms of folic acid if you could become pregnant. And if you take methotrexate or an anti-epileptic, follow the prescriber's folic acid plan. UK fortification of non-wholemeal flour with folic acid, due from late 2026, will raise baseline intakes for everyone. Our guide to what B complex is for places folate among the other B vitamins; a complex at 100 to 200% of the reference intake is a reasonable hedge for a narrow diet, below the 1 mg guidance.

What we don't know

• Whether folate deficiency alone causes nerve damage. Occasional reports; usually B12 is involved.
• The best threshold for serum folate. Laboratories vary; around 3 micrograms per litre is typical.¹

Frequently asked questions

What are the signs of folic acid deficiency?

Tiredness, breathlessness, pallor, a sore red tongue, mouth ulcers, irritability, low mood and poor concentration, sometimes with diarrhoea and poor appetite.¹

What is the most common cause of folate deficiency?

Not eating enough green vegetables, pulses and fortified foods, often combined with heavy drinking. Pregnancy, gut disease and some medicines follow.²

Is vitamin B12 the same thing as folate?

No. They are different vitamins that work together to make red blood cells, so a shortage of either causes the same anaemia. B12 deficiency also damages nerves; folate deficiency usually does not.

Can folate deficiency cause memory loss?

It can cause poor concentration and forgetfulness that improve with treatment; marked memory change is more typical of B12 deficiency and should prompt that test.

How do you fix folate deficiency?

Prescribed folic acid, usually 5 mg a day for about four months, plus a diet with greens, pulses and fortified foods, after B12 has been checked.^{1, 3}

Sources

1. NHS. Vitamin B12 or folate deficiency anaemia. nhs.uk.
2. Green R, et al. Vitamin B12 deficiency. Nature Reviews Disease Primers, 2017. PubMed 28660890.
3. Miller JW, et al. Excess folic acid and vitamin B12 deficiency: clinical implications? Food and Nutrition Bulletin, 2024. PubMed 38987872.
4. Viswanathan M, et al. Folic acid supplementation to prevent neural tube defects: updated evidence report and systematic review for the US Preventive Services Task Force. JAMA, 2023. PubMed 37526714.

This article is general information, not medical advice. Symptoms of anaemia need a GP blood test for folate, B12 and iron together; do not start folic acid for a suspected deficiency before B12 has been checked.