Flashcards in 31 - Vitamins Deck (44)
What should you focus on
Folate and methylation
What are vitamins?
Heterogeneous group of organic compounds required in small amounts for cellular functions; cannot be synthesized in adequate amounts
What are the biological roles of vitamins?
- Essential cofactors in enzymatic reactions
- Biological regulatory molecules
Describe the solubility of vitamins
Water soluble vitamins
- Vitamin B
- Vitamin C
- Circulate free (not stored)
Fat soluble vitamins
- Vitamin A
- Vitamin D
- Vitamin E
- Vitamin K
- Absorbed with bile salts
- Require carriers and stored in body fat
What are the daily recommendations for vitamins?
Recommended by Food and Nutrition Board of the Institute of Medicine – based on optimal nutritional intakes for large populations of healthy individuals
- Dietary Reference Intake (DRI)
- Recommended Dietary Allowance (RDA)
- Adequate Intake (AI)
- Estimated Average Requirement (EAR)
Just different recommendation systems
Describe the DRI
Dietary reference intake
Used to plan and assess
nutrient intakes of healthy people; vary by gender/life stage
Recommended dietary allowance
Average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%-98%) healthy people
Established when evidence is insufficient to develop an RDA and is set at a level assumed to ensure nutritional adequacy
Estimated average requirement
Expected to satisfy the needs of 50% of the people in that age group based on a review of the scientific literature.
What are the functions of vitamin B?
- Energy releasing quality
- Hematopoietic quality
What is the joint role of folate and cobalamin (B12)?
- Joint role in one-carbon transfer pathway
- Necessary for production and maintenance of new cells, DNA/RNA synthesis
Describe the relationship between folate and cobalamin
Folate works as a substrate for cobalamin
Describe the effects a deficiency of coabalamin
- Deficiency of cobalamin can lead to a “methyl trap” in methylation pathway
- Cobalmin deficiency – pernicious anemia
Describe the effects of folate deficiency
- Megaloblastic anemia
- Neural tube defects (during pregnancy)
Describe the clinical effects of nutritional anemia
- Pale skin
Describe the methylation pathway
- Homocystine needs to be converted back to cysteine so it can contribute to cell proliferation, RNA synthesis, etc.
- The other side of the pathway uses dietary folate to form purine and pyrimidine synthesis
- In about 10-15% of the population, there is a deformity in the methyltetrahydrofolate
- The defect means you need more folate in your diet to keep the pathway going
What are the sources of B12 (cobalamin)?
Animal sources only
Describe the absorption of B12 (cobalamin)
- Absorbed via intrinsic factor
- Any interruption along pathway (absorption, transport, excretion) can result in deficiency of B12
What does cobalamin deficiency lead to?
- Most common B12 deficiency
- Parietal cells fail to secrete intrinsic factor
What people is cobalamin deficiency is common in?
- Risk increases with age (occurring in up to 15% of elderly)
- Gastrointestinal conditions/surgeries
- Atrophic gastritis
- Autoimmune destruction of gastric mucosa
- Gastric bypass
- Diphyllobothrium latum – tapeworm from eating raw fish
How do you diagnose cobalamin deficiency?
Macrocytosis on CBC, peripheral blood smear, cobalamin levels, elevated methylmalonic acid and homocysteine levels, Schilling test (measures B12 and IF deficiency)
What is the overall outcome of coabalamin deficeincy?
Neurologic abnormalities due to demyelination of nerves
What is the result of folate deficiency?
- Maturation of hematopoietic precursor cells is disrupted due to defect in DNA synthesis
- White and red blood cells are enlarged
- Many cells die in bone marrow which leads to anemia
Describe the symptoms of megaloblastic anemia
- Symptoms are largely indistinguishable from pernicious anemia
- More often malnourished than those with cobalamin deficiency
- Diarrhea is often present
Neurologic abnormalities do not occur
What are the stages of folate deficiency?
- Negative folate balance (decreased serum folate)
- Decreased RBC folate levels and hypersegmented neutrophils
- Macroovalocytes, increased MCV, and decreased hemoglobin
Describe the effect of folate deficiency on the cellular level
- Requirement of THF for synthesis of purine and pyrimidines is likely the basis of the development of megaloblastic anemia (hematopoiesis requires DNA synthesis for continuing cell production)
- B12 not used for methyl donor for reactions involving DNA synthesis
- “Methyl Trap”
- Hypersegmented neutrophils
Describe the neural tube defects associated with folate deficiency
- Folate deficiency in first trimester leads to an increased risk of neural tube defects (e.g. spina bifida)
- Possibly due to increased DNA synthesis and/or increased homocysteine concentrations
- Supplementation before and during pregnancy dramatically decreases incidence of neural tube defects
- 1998 US decided to supplement all cereal grain products
- Serum folate increased 2.5 fold in US population
Describe the relationship between serum B12 and folate
- When B12 is low and folate is normal, macrocytosis anemia and cognitive impairment occur
- When B12 is normal and folate is high, there is no cognitive impairment
- When B12 is low and folate is high, there is a 5x increase in the occurrence of cognitive impairment because high folate can mask a B12 deficiency***
Describe reactive species and antioxidants
Reactive oxygen/nitrogen species – highly reactive free radicals due to imbalance of electrons
Formed with exposure to chemicals, drugs, ionizing radiation, normal physiological processes (e.g. electron transport chain), etc.
“Antioxidant” refers to any molecule capable of stabilizing or deactivating free radicals before they attack cells - act as electron donors to stabilize the reactive species – different types based on solubility