Folate (Vitamin B9)

Folate is the natural form of vitamin B9, found in leafy greens, legumes, eggs and liver. Folic acid is the synthetic form added to fortified flour and supplements. Both are required for one-carbon transfers — most critically for DNA synthesis. The body holds only modest folate reserves (months, not years like B12), so dietary insufficiency manifests faster. The most consequential deficiency is in early pregnancy: inadequate folate at conception substantially raises the risk of neural-tube defects in the fetus, which is why pre-conception supplementation is universally recommended.

• Recent supplementation — almost always the cause.
• Excessive intake from fortified foods plus supplements — generally benign, but very high folate can mask B12 deficiency on routine labs.
• High values are usually not clinically actionable.

• Poor diet, alcoholism — most common.
• Malabsorption — coeliac disease, Crohn's, bariatric surgery.
• Methotrexate, trimethoprim, phenytoin, sulfasalazine — drugs that interfere with folate metabolism.
• Increased need — pregnancy, lactation, chronic haemolysis.
• Always check B12 alongside folate — pure B12 deficiency can drive folate appearance into similar tissue patterns; treating folate alone in a B12-deficient patient can precipitate irreversible neurological injury.