Vitamin B12 and Folic Acid — MCQs
Which vitamin is required for transfer of 1-carbon unit?
Which vitamin deficiency leads to megaloblastic anemia?
Methyl-tetrahydrofolate (5-methyl-THF) gets accumulated in deficiency of which of the following?
Leucovorin is used for side effect reduction in which anticancer drug?
In cobalamin deficiency which is not seen
Megaloblastic anemia should be treated with both folic acid and vitamin B12 because -
What is the appropriate treatment for megaloblastic anemia with neurological symptoms?
Following complete ileal and partial jejunal resection, the patient is most likely to have-
Vitamin B12 is found maximum in:
Which of the following is the richest source of vitamin B12?
Vitamin B12 and Folic Acid Indian Medical PG Practice Questions and MCQs
Question 1: Which vitamin is required for transfer of 1-carbon unit?
- A. Niacin
- B. Vitamin B12
- C. Vitamin A
- D. Folic acid (Correct Answer)
Explanation: ***Folic acid*** - **Folic acid** (vitamin B9) is essential for the transfer of **one-carbon units**, particularly as **tetrahydrofolate (THF)**. - These one-carbon units are critical in metabolic processes such as **DNA synthesis**, **amino acid metabolism**, and **neurotransmitter synthesis**. *Vitamin A* - **Vitamin A** (retinol) is primarily involved in **vision**, **immune function**, and **cell differentiation**. - It does not play a direct role in the transfer of one-carbon units. *Vitamin B12* - **Vitamin B12** (cobalamin) is involved in two main reactions: the conversion of **methylmalonyl-CoA to succinyl-CoA** and the transfer of a **methyl group from N5-methyl THF to homocysteine** to form methionine. - While it works with folate, it does not directly transfer one-carbon units in the same way as folic acid. *Niacin* - **Niacin** (vitamin B3) is a precursor to **NAD+ and NADP+**, which are crucial coenzymes in **redox reactions** and energy metabolism. - It is not involved in the transfer of one-carbon units.
Question 2: Which vitamin deficiency leads to megaloblastic anemia?
- A. Riboflavin
- B. Folate (Correct Answer)
- C. Vitamin C
- D. Niacin
Explanation: ***Folate*** - **Folate** is essential for DNA synthesis; a deficiency impairs erythrocyte maturation, leading to the production of **large, immature red blood cells** (megaloblasts) [3]. - This vitamin deficiency also presents with symptoms like **fatigue, glossitis**, and neurologic manifestations are absent unlike vitamin B12 deficiency [1]. *Riboflavin* - **Riboflavin (Vitamin B2)** deficiency can cause **normocytic anemia**, but generally not megaloblastic anemia. - Its deficiency is mainly associated with **angular stomatitis, cheilosis**, and ocular symptoms. *Vitamin C* - **Vitamin C** deficiency (scurvy) is associated with impaired collagen synthesis, leading to **gingival bleeding, petechiae**, and poor wound healing. - While it can cause some anemia, it is typically **microcytic** due to impaired iron absorption if it affects iron metabolism, not megaloblastic [2]. *Niacin* - **Niacin (Vitamin B3)** deficiency causes **pellagra**, characterized by the "3 D's": **dermatitis, diarrhea, and dementia**. - It does not directly lead to megaloblastic anemia, as it is not involved in a critical step of DNA synthesis in the same way folate is.
Question 3: Methyl-tetrahydrofolate (5-methyl-THF) gets accumulated in deficiency of which of the following?
- A. Vitamin B12 (Cobalamin) (Correct Answer)
- B. Vitamin B2 (Riboflavin)
- C. Vitamin B1 (Thiamine)
- D. Vitamin B6 (Pyridoxine)
Explanation: ***Vitamin B12 (Cobalamin)*** - A deficiency in **Vitamin B12** (cobalamin) leads to the accumulation of **5-methyl-tetrahydrofolate (5-methyl-THF)** due to the **"folate trap"** hypothesis. - This occurs because B12 is a cofactor for **methionine synthase**, which converts 5-methyl-THF back to tetrahydrofolate (THF), a necessary step for DNA synthesis and other one-carbon metabolism reactions. - Without B12, folate remains trapped in the methyl form and cannot be utilized for other essential reactions. *Vitamin B2 (Riboflavin)* - **Vitamin B2** (riboflavin) is a precursor for **FAD** and **FMN**, essential coenzymes in various redox reactions in the electron transport chain and other metabolic pathways. - Its deficiency typically presents as **cheilosis**, glossitis, and angular stomatitis, but does not cause methyl-THF accumulation. *Vitamin B1 (Thiamine)* - **Vitamin B1** (thiamine) is a cofactor for enzymes like **pyruvate dehydrogenase** and **alpha-ketoglutarate dehydrogenase** in carbohydrate metabolism. - Its deficiency causes **Beriberi** (wet, dry, or Wernicke-Korsakoff syndrome), affecting the cardiovascular and nervous systems, but does not affect folate metabolism. *Vitamin B6 (Pyridoxine)* - **Vitamin B6** (pyridoxine) is a coenzyme for many metabolic reactions, particularly in amino acid metabolism and neurotransmitter synthesis. - Deficiency can lead to **sideroblastic anemia**, neurological symptoms, and dermatitis, but does not cause methyl-THF accumulation.
Question 4: Leucovorin is used for side effect reduction in which anticancer drug?
- A. Cisplatin
- B. 5-FU
- C. Adriamycin
- D. Methotrexate (Correct Answer)
Explanation: ***Methotrexate*** - **Leucovorin rescue** is a critical adjunct therapy for **methotrexate** to prevent severe toxicity. - Methotrexate is a **folate antagonist**, and leucovorin (folinic acid) provides a reduced folate form that bypasses the blocked enzyme, restoring normal cellular function and protecting healthy cells. - This is true **"rescue therapy"** - leucovorin protects normal cells from methotrexate toxicity. *Cisplatin* - **Cisplatin** is a platinum-based chemotherapy drug primarily associated with **nephrotoxicity** and **ototoxicity**. - Its side effects are managed with **hydration, amifostine**, and antiemetics, not leucovorin. *5-FU* - **5-FU (5-fluorouracil)** is a pyrimidine analog that can cause severe **myelosuppression** and **gastrointestinal toxicity**. - While leucovorin is used WITH 5-FU (e.g., in colorectal cancer regimens), it serves to **enhance/potentiate** 5-FU's cytotoxic effect through biochemical modulation, NOT to rescue from toxicity. - This is the key distinction: leucovorin + 5-FU = **potentiation**; leucovorin + methotrexate = **rescue**. *Adriamycin* - **Adriamycin (doxorubicin)** is an **anthracycline antibiotic** known for causing **cardiotoxicity** and **myelosuppression**. - **Dexrazoxane** is used to prevent Adriamycin-induced cardiotoxicity, not leucovorin.
Question 5: In cobalamin deficiency which is not seen
- A. Loss of proprioception
- B. Rhomberg sign
- C. Microcytic anemia (Correct Answer)
- D. Long tract signs
Explanation: Microcytic anemia - Cobalamin deficiency typically leads to macrocytic anemia due to impaired DNA synthesis, not microcytic anemia [1]. - Microcytic anemia is usually associated with iron deficiency, thalassemia, or anemia of chronic disease [1]. Long tract signs - Long tract signs are common in cobalamin deficiency due to posterior column and corticospinal tract involvement leading to symptoms like spasticity. - They indicate involvement of pathways that are affected by vitamin B12 deficiency. Loss of proprioception - Loss of proprioception can occur in cobalamin deficiency due to damage to the dorsal columns of the spinal cord. - It is a common clinical finding indicating the involvement of sensory pathways. Rhomberg sign - A positive Rhomberg sign indicates impaired proprioception, which can happen in cobalamin deficiency. - It reflects difficulty maintaining balance, emphasizing sensory dysfunction associated with the deficiency.
Question 6: Megaloblastic anemia should be treated with both folic acid and vitamin B12 because -
- A. It is an enzyme
- B. It is a cofactor
- C. Folic acid alone causes improvement of hematologic symptoms but worsening of neurological symptoms (Correct Answer)
- D. None of the above
Explanation: ***Folic acid alone causes improvement of hematologic symptoms but worsening of neurological symptoms*** - Treating **B12 deficiency** with **folic acid alone** can normalize hematologic parameters, which can mask the underlying B12 deficiency. - This can lead to the progression of **irreversible neurological damage** because folic acid does not address the metabolic pathways dependent on B12 for myelin maintenance. *It is an enzyme* - **Folic acid** and **vitamin B12** are not enzymes; they function as **coenzymes** or **cofactors** in metabolic reactions. - Enzymes are proteins that catalyze biochemical reactions, a role not played by these vitamins themselves. *It is a cofactor* - While both **folic acid** and **vitamin B12** are cofactors, this statement alone does not explain why both are needed to treat megaloblastic anemia. - The critical reason for co-administration lies in the potential for **neurological deterioration** if B12 deficiency is missed and only folate is given. *None of the above* - This option is incorrect because there is a valid and specific reason (the neurological consequences mentioned above) for treating megaloblastic anemia with both supplements. - The interaction between **folate** and **B12 metabolism** is crucial in understanding the treatment approach.
Question 7: What is the appropriate treatment for megaloblastic anemia with neurological symptoms?
- A. Iron supplementation
- B. Folic acid with Hydroxycobalamin (Correct Answer)
- C. Vitamin B1 supplementation
- D. Folic Acid only
Explanation: Folic acid with Hydroxycobalamin - Neurological symptoms in megaloblastic anemia strongly suggest vitamin B12 deficiency, as folic acid alone can mask this deficiency and worsen neurological sequelae [3]. - Hydroxycobalamin is the preferred treatment for vitamin B12 deficiency, while folic acid addresses the megaloblastic hematopoiesis. Iron supplementation - This is used to treat iron deficiency anemia, which presents with microcytic or normocytic red blood cells, not megaloblastic changes [1]. - Iron supplementation would not address the neurological symptoms or the underlying B12 or folate deficiency. Vitamin B1 supplementation - Vitamin B1 (thiamine) deficiency is associated with conditions like beriberi and Wernicke-Korsakoff syndrome, characterized by neurological symptoms, but not megaloblastic anemia [4]. - Supplementation would not correct the underlying hematological abnormality or the specific neurological symptoms of B12 deficiency [4]. Folic Acid only - While folic acid is essential for DNA synthesis and would improve the hematological parameters of megaloblastic anemia, it does not treat vitamin B12 deficiency [2]. - Giving folic acid alone in the presence of B12 deficiency can lead to a worsening of neurological symptoms as it can correct the anemia but allow the neurological damage to progress [3].
Question 8: Following complete ileal and partial jejunal resection, the patient is most likely to have-
- A. Constipation
- B. Gastric ulcer
- C. Folic acid deficiency
- D. Vitamin B12 Deficiency (Correct Answer)
Explanation: ***Vitamin B12 Deficiency*** - The **terminal ileum** is the primary site for **vitamin B12 absorption**, complexed with intrinsic factor [3]. Resection of this segment significantly impairs this process. - Patients with **ileal resection** are highly susceptible to developing **megaloblastic anemia** and neurological complications due to **vitamin B12 deficiency** [3]. *Constipation* - Complete ileal and partial jejunal resection is **more likely to cause diarrhea** rather than constipation, particularly due to malabsorption of bile salts and fats [2]. - **Bile salt malabsorption** in the colon often leads to secretory diarrhea [1]. *Gastric ulcer* - Gastric ulcers are typically associated with *Helicobacter pylori* infection or NSAID use, and are **not a direct consequence** of ileal and jejunal resection. - While short bowel syndrome can sometimes lead to increased gastric acid secretion, peptic ulcer formation is not the most likely or direct complication. *Folic acid deficiency* - **Folic acid** is primarily absorbed in the **jejunum**, and while partial jejunal resection occurred, complete ileal resection is less directly implicated in folate deficiency. - Other sections of the small intestine can often compensate for partial jejunal loss in folate absorption, making B12 deficiency a more immediate and severe concern after complete ileal resection.
Question 9: Vitamin B12 is found maximum in:
- A. Sunlight
- B. Green leafy vegetables
- C. Animal products (Correct Answer)
- D. Roots and tubers
Explanation: ***Animal products*** - **Vitamin B12**, or cobalamin, is primarily synthesized by bacteria and accumulates in animal tissues, making **meat, fish, poultry, eggs, and dairy** the richest dietary sources. - Humans generally cannot synthesize vitamin B12 and must obtain it from dietary sources, with **animal-derived foods** being the most concentrated and bioavailable forms. *Sunlight* - **Sunlight** is primarily critical for the synthesis of **Vitamin D** in the skin, not Vitamin B12. - Exposure to sunlight has no direct role in the production or absorption of **Vitamin B12**. *Green leafy vegetables* - **Green leafy vegetables** are excellent sources of nutrients like **folate, Vitamin K, and iron**, but they are generally devoid of naturally occurring **Vitamin B12**. - While some fortified plant-based foods may contain Vitamin B12, naturally, these vegetables do not provide it. *Roots and tubers* - **Roots and tubers** like potatoes, carrots, and sweet potatoes are good sources of carbohydrates, fiber, and various vitamins and minerals such as **Vitamin C and potassium**. - They do not contain significant amounts of **Vitamin B12**, as they are plant-based foods.
Question 10: Which of the following is the richest source of vitamin B12?
- A. Meat (Correct Answer)
- B. Green leafy vegetables
- C. Corn oil
- D. Sunflower oil
Explanation: ***Meat*** - **Meat** and other animal products are the primary natural dietary sources of **vitamin B12** (cobalamin). - This is because vitamin B12 is synthesized by bacteria and accumulates in animal tissues. *Green leafy vegetables* - **Green leafy vegetables** are excellent sources of many vitamins and minerals, such as **folate** and **vitamin K**, but they do not contain vitamin B12. - Vitamin B12 is essentially absent in plant-based foods unless they are fortified or contaminated. *Corn oil* - **Corn oil** is a vegetable oil primarily composed of fats and is a source of **vitamin E** and fatty acids, but it does not contain vitamin B12. - Oils derived from plants lack intrinsic vitamin B12 content. *Sunflower oil* - Similar to corn oil, **sunflower oil** is a plant-based oil rich in **vitamin E** and unsaturated fatty acids, but it contains **no vitamin B12**. - Plant oils are not a source of vitamin B12, which is almost exclusively found in animal products.
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