Lecture 3 - Vitamin B12 Flashcards
what food group is a rich source of vitamin B12
animal products
why is vitamin B12 fortification very important for vegans
they do not consume animal products
why is marmite not a very good source of vitamin B12
although there is a lot of B12 in marmite per 100 grams, we don’t consume enough for this to be an adequate source of B12
what is another issue with marmite and why it isnt a very good source of vitamin B12
very high in sodium, so if over consumed have negative health effects
where does vitamin B12 actually come from
bacteria
how does B12 get into the foods we eat
bacteria produce B12 in the cow (has to do with their rumen) this goes into our meat and milk
also fish and chicken have B12
commercial production of vitamin B12 happens how
large scale production via microbial fermentation
commercial production of vitamin B12 predominantly uses how many strains of bacteria
three strains
Vitamin B12 is the term used for what
the term used for all corrinoids that have biological activity of “cyancobalamin”
what is the molecular weight if B12 like compared to other vitamins
Big molecular weight
what is the chemical structure of vitamin B12
corrin ring (4 pyrrole rings) with a colbalt in centre and dimethylbezimidazole nucleotide
what determines what type of corrinoid it is
whatever is bound to the colbalt in the centre of the corrin ring
what are three examples of corrinoids and what can be bound to the colbalt
cyanocobalamin
methylcobalamin
deoxyadenosylcobalamin
what are the active forms of B12
methylcobalamin
deoxyadenosylcobalamin
what is the stable form of B12 and what is this used for
cyanocobalamin
most common form used for supplements
what is cobalamin very sensitive to
very sensitive to acid
what must happen to cobalamin and protein before it can be digested
cobalamin must be removed from protein for the body to use it
why is the removal of cobalamin from a protein problematic
because this is done by an acid and cobalamin is very sensitive to acid
cobalamin from the diet is bound to what
protein
as cobalamin is swallowed what is released at the same time
haptocorrin
what happens in the stomach to cobalamin and why is it volunerable
HCL is released and this breaks off the protein from cobalamin (vulnerable to attack by the acid)
what will haptocorrin do and what does this mean
will bind to B12
- binding to the cobalamin as soon as it released from the protein, protects it from acid attack
what happens to cobalamin in the duodenum
proteases will split haptocorrin from the cobalamin
why is it fine for cobalamin to be unbound in the duodenum
more alkaline space
what does your body need in order to absorb cobalamin
transporter that will enable it to bind to a receptor
what is the role of intrinsic factor regarding cobalamin
intrinsic factor is released from the stomach, will bind to cobalamin in the duodenum and can transport it into the ileal cell through the receptor
is B12 water soluble or water insoluble
water soluble
absorbed cobalamin is later what
later recycled after excreted in bile
what are two enzymes that are B12 dependent
methylmalonyl-CoA mutase
methionine synthase
what is the role of methylmalonyl-CoA mutase enzyme
conversion of methylmalonyl CoA > succinyl CoA
what is the role of methionine synthase
transfer methyl group from 5MTHF to homocysteine, to form methionine
if you do not have enough vitamin B12, you will not have enough adenosylcobalamine and what does this mean
you will not have enough 1-Methylmalonyl-CoA mutase
if you have insufficient 1-Methylmalonyl-CoA mutase then what will you not be producing enough of and why is this important
succinyl-CoA = important in the citric acid cycle
if you have insufficient 1-Methylmalonyl-CoA mutase then you will have a build up of what and what will this produce more of
methylmalonyl-CoA, so more methylmalonic aicd will be produced
a build up of methylmalonyl-CoA also leads to a build up of propinoyl-CoA and what does this cause
propionic acid from gut flora
odd chain fatty acids
what is the enzyme that converts a methyl group onto homocysteine to form methionine and when can this be inhibited
methionine synthase - when there is not enough B12 to support methionine synthase activity
in the methylfolate trap what will happen to the levels of 5MTHF and why
there will be higher levels, because can not go through the pathway due to methionine synthase problems
in the methylfolate trap what will happen to the levels of THF and why
there will be lower levels, the pathway is getting jammed up at 5MTHF, it can not get converted back to THF
in the methylfolate trap what will happen to the levels of 5,10-methylene THF and why
there will be lower levels, less THF so less being converted to 5,10-methylene THF
in the methylfolate trap what will happen to DNA synthesis
DNA synthesis will decrease
in history of viramin B12 in 1849 what were the complications described, was there treatment and was it fatal ?
clinical symptoms of pernicious (harmful in a gradual way) anaemia described
- no treatment (vitamin B12 not discovered yet)
- fatal
in history of viramin B12 in 1926 it was found eating what helped patients with pernicious anaemia
eating raw liver
when was vitamin B12 named
1948
what is pernicious anaemia
lack of intrinsic factor
lack of intrinsic factor is a what and what does this do
autoimmune disease = attacks parietal cells which limits or eliminates production of intrinsic factor
how is a vitamin B12 deficiency due to lack of intrinsic factor treated and why
treated with B12 intramuscular injection (because it will only be absorbed if there is intrinsic factor so have to inject B12)
how is B12 deficiency caused by lack of stomach acid (limited and absent) and what does this do
limited (hypochlorhydria) or absent (achlorhydria) production of HCL
lessens B12 release from animal protein
lack of stomach acid related to vitamin B12 deficiency most commonly affects who
elderly
what are the two types of gastrointestinal damage that can lead to vitamin B12 deficiency
Crohn’s disease
Gastric bypass
what is crohn’s disease
a type of inflammatory bowel disease which may inflame the small intestine and reduce B12 absorption
what is gastric bypass
procedures that reduce the stomach area secreting stomach acid which can lead to reduced B12 absorption
there are 12 inherited errors of metabolism that have been identified and these affect : (4) (are they manageable)
- intestinal absorption
- transport in the blood
- cellular uptake
- intracellular metabolism
some are manageable, some are incompatible with life
what infants are particularly susceptible to vitamin B12 deficiency
breastfed infants with vegan mothers
megaloblastic anaemia has to do with vitamin B12 because of whay
methylfolate trap
what is vitamin B12 neuropathy
“subacute combined degeneration of the cord”
- demyelination of motor neurons
what are the symptoms of vitamin B12 neuropathy
- loss of position sense
- spasms and weakness of lower limbs
- cognitive changes - memory loss due to dementia
- may be irreversible
what is the biochemistry to vitamin B12 neuropathy
impaired methylation of myelin basic protein due to deficient methionine synthase activity
what is the upper limit of vitamin B12
not possible to set
- no evidence of harm from several hundred times the requirement
what is the EAR and RDI of vitamin B12 in adult men and women
EAR : 2.0μg/day
RDI: 2.4μg/day
what is the eating and activity guidelines around plant based milk alternatives linked to B12, vitamin D and calcium
if choosing plant based milks choose products fortified with calcium, vitamin D and vitamin B12
what products are permitted to be fortified with B12 in NZ
- extracts of meat, vegetables or yeast
- analogues of meat
- legume protein containing foods
