Folic acid (Folate)

Vitamin (water-soluble)

• UK RNI 200 mcg
• US RDA 200 mcg

Functions

• Blood formation
• Protein, RNA and DNA synthesis
• Synthesis of purines and pyrimidines
• Synthesis of the amino acids glycine and methionine

Good food sources

• Leafy green vegetables, especially raw spinach
• Liver
• Freshly squeezed orange juice
• Soya flour
• Whole grains
• Yeast extract

Deficiency signs and symptoms

• Anaemia
• Anorexia
• Apathy
• Birth defects in children
• Breathlessness
• Constipation and digestive disturbances
• Fatigue
• Growth impairment
• Habitual miscarriage
• Increased risk of cancer
• Increased risk of heart disease (by causing raised homocysteine levels)
• Insomnia
• Memory impairment
• Mental confusion
• Reduced immunity
• Sore tongue
• Weakness

Low levels of several B vitamins have been found in psychiatric patients and in senile dementia.

Preventing deficiency

Folic acid is one of the vitamins most easily destroyed by heat, therefore vegetables should be cooked for as short a time as possible. Whole grains rather than their refined counterparts should be eaten as regularly as possible. The cumulative losses of folic acid which occur during food processing often amount to 65 per cent, leaving many foods with only one third of their original folic acid content. Prolonged boiling alone can cause losses of up to 50 per cent. Like vitamin B2, folic acid is sensitive to light. The bioavailability of folic acid is reduced by alcohol intake, the contraceptive pill, aspirin, cimetidine (Zantac), antacids, zinc deficiency, vitamin B12 deficiency, and the ageing process. Folic acid deficiency is relatively common in malnourished hospitalized patients. Certain tissues can be more folate-deficient than others: for instance precancerous changes can occur in the cervix, lung or colon which are reversible with folic acid supplementation (Heimburger DC: Localized deficiencies of folic acid in aerodigestive tissues. Ann NY Acad Sci 669:87-95, 1992).

Vitamin B12 deficiency causes folate deficiency by causing folic acid to be trapped as methylfolate, which is unavailable to the body. A deficiency of the amino acid methionine has a similar effect. Oral contraceptives also prevent adequate utilization.

Comments

Folic acid itself does not occur in food or human tissue unless taken as a dietary supplement, and it is physiologically inactive until it has been reduced to dihydrofolic acid. Folic acid is in fact the parent molecule for a number of derivatives known collectively as folates. The main circulating folate is known as 5-methyl tetrahydrofolate, but the active forms inside cells are known as polyglutamates.

SUPPLEMENTATION

In research studies, folic acid supplements have been found to:

• Prevent spina bifida in the unborn
• Treat megaloblastic, aplastic and sickle cell anaemias (if folic acid is deficient)
• Reduce levels of harmful homocysteine (which is linked with heart disease and osteoporosis)
• Reverse cervical dysplasia (pre-cancerous condition of the cervix)
• Treat depression and schizophrenia

Preferred form and suggested intake

B vitamins should not normally be taken singly, since they work together as a team and good nutrition is about avoiding imbalances. A B complex supplement providing 200-400 mcg of folic acid is enough for most purposes.

Cautions

Megadoses of folic acid as given by many doctors to pregnant women (often 4,000 mcg or more) are unnecessary and may reduce zinc absorption.

Folic acid supplements given to patients who may be developing a vitamin B12 deficiency may obscure a correct diagnosis and delay the appropriate treatment.