Folic acid (also called folate or vitamin B9) is a water-soluble vitamin essential for DNA synthesis, red blood cell formation, and fetal development. It is extremely high-yield for exams, especially questions related to megaloblastic anemia, pregnancy, and homocysteine metabolism.
What Is Folic Acid?
Folic acid is the synthetic form of folate, a B-complex vitamin required for one-carbon transfer reactions in the body.
One-Line Definition
Folic acid is a vitamin required for DNA synthesis and red blood cell maturation
Natural Folate vs Folic Acid
| Feature | Folate | Folic Acid |
|---|---|---|
| Source | Green vegetables, legumes | Supplements, fortified foods |
| Stability | Less stable | More stable |
| Use | Dietary | Therapeutic |
Why Folic Acid Is Essential
Folic acid is crucial for:
1. DNA synthesisRapidly dividing cells (bone marrow, fetus) are most affected by deficiency.
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Mechanism of Action (Very High-Yield)
Folic acid is converted into its active form tetrahydrofolate (THF).
Step-by-Step Mechanism
1. Folic acid → Dihydrofolate (DHF)3. THF participates in one-carbon transfer reactions
4. Required for:
- Purine synthesis
- Thymidylate (dTMP) synthesis
One-Line Exam Answer
Folic acid supports DNA synthesis by providing tetrahydrofolate for one-carbon transfer reactions
Role in Homocysteine Metabolism (Exam Favorite)
Folic acid:
- Converts homocysteine → methionine
- Works with vitamin B12
Deficiency → ↑ homocysteine → ↑ cardiovascular risk
Clinical Uses of Folic Acid
1. Megaloblastic Anemia (Very High-Yield)
1. Due to folate deficiency- Macrocytosis
- Hypersegmented neutrophils
2. Pregnancy & Pre-Conception Care (Must-Know)
Folic acid prevents:
Neural tube defects (NTDs):
- Spina bifida
- Anencephaly
Given before conception and during early pregnancy
3. Hyperhomocysteinemia
- Reduces homocysteine levels
- Used with B6 and B12
4. Drug-Induced Folate Deficiency
Used with:
- Methotrexate (low-dose rescue)
- Phenytoin
- Trimethoprim
Causes of Folic Acid Deficiency
Dietary
- Poor nutrition
- Alcoholism
Increased Demand
- Pregnancy
- Hemolytic anemia
Malabsorption
- Celiac disease
- Tropical sprue
Drugs
- Methotrexate
- Phenytoin
- Trimethoprim
Clinical Features of Folic Acid Deficiency
Hematologic
- Megaloblastic anemia
- Fatigue
- Pallor
GI
- Glossitis
- Diarrhea
Neurologic
No neurological symptoms(important distinction from vitamin B12 deficiency)
Folic Acid vs Vitamin B12 (Classic Exam Comparison)
| Feature | Folic Acid | Vitamin B12 |
|---|---|---|
| Anemia | Megaloblastic | Megaloblastic |
| Neuropathy | ❌ No | ✔ Yes |
| Homocysteine | ↑ | ↑ |
| MMA | Normal | ↑ |
Folic acid corrects anemia but not neuropathy of B12 deficiency
Adverse Effects
Folic acid is very safe.
Rare
- GI upset
- Allergic reactions (very rare)
High doses may mask vitamin B12 deficiency
Contraindications & Cautions
Always rule out vitamin B12 deficiency before treating anemia with folic acid alone.Important Exam-Oriented Pearls
- Folic acid deficiency → megaloblastic anemia without neuropathy
- Essential in pregnancy
- ↓ Homocysteine
- Methotrexate is a folic acid antagonist
- Water-soluble → excess excreted in urine
Easy Memory Tricks
- “FOLIC = For DNA & Fetus”
- “No Folate → No Nucleotides”
- “B12 = Brain, Folate = Blood”
FAQs
1. What is the main function of folic acid?
It is required for DNA synthesis and red blood cell formation.
2. Which anemia is caused by folic acid deficiency?
Megaloblastic anemia.
3. Does folic acid cause neurological symptoms when deficient?
No.
4. Why is folic acid given in pregnancy?
To prevent neural tube defects.
5. Can folic acid lower homocysteine levels?
Yes.
6. Which drugs cause folate deficiency?
Methotrexate, phenytoin, trimethoprim.
7. Is folic acid water-soluble?
Yes.
8. Can folic acid mask vitamin B12 deficiency?
Yes, especially hematologic signs.
9. Is folic acid safe?
Yes, it has an excellent safety profile.
10. When should folic acid be started in pregnancy?
Before conception and during early pregnancy.
