Folic acid deficiency can be caused by a wide range of factors:

1. Increased physiological requirements like pregnancy have increased demand for folate which may lead to a deficiency
2. Dietary insufficiency of folate-rich foods
3. Malabsorption of folate due to gastrointestinal conditions, alcoholism, and inhibition from drugs like methotrexate and phenytoin
4. Mutations of the methylenetetrahydrofolate reductase gene, or MTHFR, may contribute to deficiency