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Flashcards in Folate and B12 Deck (16):
1

Folate RDA

400 mcg/day adults
600 mcg/day in pregnancy (up to 1 mg)

5-methyltetrahydrofolate = most active form

2

Folate absorption/availability

destroyed by heat, oxidation, light, processing
approx 50% absorbed
- hydrolyzed to monoglutamate by carboxypeptidase on brush border (zinc dependent)
absorption inhibited by
- alcohol
- legumes, lentils
- cabbage
- oranges

3

Folate functions

coenzyme for transfer of one-carbon units
- nucleic acid (DNA) and AA (met, his, gly, ser) metabolism
- methylation rxns

4

Functions of folate-dependent methylation

gene regulation
detox
neurotransmitter synthesis and metabolism (DA and EPI)
- NE --> EPI and serotonin ---> melatonin
immune cell maturation (T and NK cells)
DNA synthesis (purine ring, RBC production)
energy production (CoQ10, carnitine, creatine, ATP)
myelin production
cell membrane synthesis/maintenance (phosphatidylcholine)

5

Folate deficiency

incr homocysteine levels
megaloblastic anemia: fatigue, weakness, SOB
neural tube defects during pregnancy
cognitive impairment: dementia
peripheral neuropathy

6

Folate toxicity

none known
may mask B12 deficiency in megaloblastic anemia

7

MTHFR SNPs

677C>T
heterozygous = 20-50% of population
homozygous = 3-32% of pop; 65% reduction in enzyme activity
---> lower folate status, diminished methylation, incr homocysteine levels

8

Folate food sources

leafy greens
mushrooms
brassicas
citrus
nuts/seeds
legumes
enriched cereals

9

Cobalamin RDA

2.4 mcg/day
forms =
*adenosylcobalamin - methylmalonyl-CoA mutase
*methylcobalamin - homocysteine methyltransferase
aquocobalamin
cyanocobalamin (inactive, often supplemented, conversion to active form questionable)

10

Cobalamin/B12 absorption

absorb 40-89%
heat/light/oxidation stable
binds to R-protein in stomach; cleaved in SI by pancreatic enzymes
binds to IF and absorbed in the ileum via cubilin
bound to transcobalamin II in the blood
** to assess test methylmalonic acid in serum or urine**

11

Cobalamin/B12 storage

mostly adenosylcobalamin
approx 50% in the liver (2-4 mg)
may take 3-5 years to develop a deficiency

12

Methylcobalamin

Homocysteine metabolism (methionine synthase)
RBC metabolism

13

Adenosylcobalamin

needed to convert methylmalonyl-CoA to succinyl-CoA
- methylmalonyl CoA mutase
{succinyl-CoA ===> TCA cycle/hemoglobin synthesis}

14

Cobalamin/B12 deficiency

megaloblastic anemia
pernicious anemia
memory loss/dementia
peripheral neuropathy

15

Cobalamin/B12 deficiency causes

reduced intake
hypochlorhydria/atrophic gastritis/H.pylori infx
malabsorption conditions/intestinal resection
medications: PPIs, H2 blockers, cholestryramine, metformin??

16

Cobalamin/B12 food sources

meat - esp seafood (clams, mussels, mackerel)
nutritional yeast
fortified foods
purple laver - porphyra spp
shiitake