Vitamin B12

Question 1

True/False: Animal products are the only reliable source of Vit B12?

Answer 1

True.

Question 2

What affect does vit C has on vit B12?

Answer 2

An excess intake of Vit C (500mg) can impair the Vit B12 bioavailability from foods and destroy the vitamin.

Question 3

Briefly describe the process of B12 absorption.

Answer 3

Thru the action of HCL and pepsin in the stomach, vit B12 is released from the ingested PRO. It then binds to a glycoprotein and travels to the SI where the complex is hydrolyzed by pancreatic proteases freeing B12 in the duodenum to bind w/ another glycoprotein Intrinsic factor (IF), which moves to ileum where it is absorbed.

Question 4

Vitamin B12 can be stored in which organs?

1. Bone marrow, liver and erythrocytes.
2. Liver
3. Bone marrow
4. Vit B12 like other water soluble vitamins is not stored.

Answer 4

2. Liver. NB: after absorption, vit B12 is transported in the plasma attached to a transport protein transcobalamin II (TC II) where it is taken up by the liver, bone marrow and erythrocytes.

Question 5

What conditions can affect Vit B12 absorption?

Answer 5

1. Pancreatic insufficiency could interfere w/ the release of B12 from IF–> decreased the amt absorbed.
2. People w/ impaired HCL production like elderly and those taking histamine antagonists or proton pump inhibitors.
3. Patients with partial or all of ileum or stomach.
4. Patients with chronic malabsorption syndromes.

Question 6

What are some function of B12?

Answer 6

1. In one of its coenzyme form, methylcobalamin, it is a cofactor for the enzyme methionine synthetase which coverts homocysteine to methionine.
2. It help converts folate into its active form. NB. when vit B12 is lacking, folate becomes trapped in its methyl, inactive form, hence the commonly misdiagnosis of folate deficiency for vit B12 deficiency.
3. In its coenzyme form, deoxyadenosylcobalamin form, it is required for the conversion of methylmalonyl conenzyme A ro succinyl coenzyme and
4. for the degradation of certain a.a and LCFA.

Question 7

List some effects of Vit B12?

Answer 7

1. Hematological: megaloblastic anemia, leukopenia (decreased in WBC), and thrombopenia.
2. GI defects: rapidly dividing and megaloblastic changes of the GI cells resulting in diarrhea, constipation and glossitis (inflammation of the tongue).
3. Neurological defects: peripheral nerve, spinal cord, or cerebral damage w/ paresthesia (stinging/burning feeling) of the hands and feet.

Question 8

What measures are used to assess Vit B12 status?

Answer 8

1. Measurement of serum level of methyl-malonic and homocysteine. Both levels are elevated in 90% of individuals w/ vit B12 deficiency.
2. Most accurate is to measure Vit B12 concentration to determine status.
3. Note, homocysteine levels may also be elevated in folic acid deficiency so its not a specific indicator for Vit B12 def.

Question 9

What is the common dose/treatment for Vit B12 deficiency?

Answer 9

1. 100 - 1000mcg IM injections at month intervals until corrected.
2. Other alternatives are sublingual, nasal spray, and gel B12 preparations.

Question 10

Because of the close interrelationship between Vit B12 and folic acid, should the status of each vitamin assess simultaneously or separate?

Answer 10

Simultaneously especially in the presence of megaloblastic anemia.