Hi Sally
In response to your question on Vegans and vitamin B12 measurements;
Many vegans (and others) are very confused on this subject. A few understand it, but most mix a little fact with a lot of misinformation
and come up with info like what is contained in your E-mail…
I will respond to each point raised:
A blood B12 level measurement is a very unreliable test for vegans,
Not true.
Cobalamin is either present in the patient’s serum or not. The current
immuno assay methods are very reliable and are specific for human active vitamin B12. There is no difference in nB12 assay based on your dietary preference.
particularly
for vegans using any form of algae. Algae and some other plant foods contain B12-analogues (false B12) that can imitate true B12 in blood tests while actually interfering with B12 metabolism.
A little bit of fact and a lot of misunderstanding. Some
algae, notably Spirulina
does contain a biologically inactive form of vitamin
B12. The problem is NOT that it imitates true B12 in blood tests, but rather it is selectively absorbed from the gut. Vegans often use
Spirulina as their vegetarian source of vitamin B12. This means that any active forms of B12 from other dietary sources have reduced absorption if the
Spirulina-sourced B12 is blocking the absorption binding sites. The
Spirulina analogue of B12 does not interfere with B12 metabolism – it prevents the absorption of bioactive analogues.
Blood counts are also unreliable as high
folate intakes suppress the anaemia symptoms of B12 deficiency that can be detected by blood counts.
Again a little fact and a lot of misunderstanding.
Vegans should have high Folate levels as a result of a plant diet…
Folate has NO impact on the measurement of B12 in serum.
Folate does mask some of the symptoms of B12 deficiency – notably neurological signs, and may mask
macrocytic (Megaloblastic) changes in the blood film. Doctors should NOT be relying on
megaloblastic changes to diagnose B12 deficiency. There is a large literature showing that as many as 80% of patients with a low enough serum B12 to result in neurological deficits show NO haematological changes at all. So this is
not an issue. If there are megaloblastic changes in the film, there is probably a B12 and/or
folate deficiency. A normal MCV and the absence of
hypersegmented neutrophils
does NOT rule out B12 deficiency.
Blood
homocysteine testing is more reliable, with levels less than
10 micromol/litre being desirable.
TRUE.
Homocysteine should be measured along with a serum B12.
Homocysteine gives a measure of BODY RESERVES of B12. The body can store 3 to 5 years worth. Reserves are adequate until
homocysteine rises above about 10
umol/L. Limitation: Renal failure,
hyperhomocysteinaemia, very high protein diet, can also elevate
homocysteine levels.
The most specific test for B12 status is
methylmalonic acid (MMA) testing. If this is in the normal range in blood (<370
nmol/L) or urine (less than 4 mcg /mg
creatinine) then your body has enough B12. Mostly
true. MMA is another very good measure of body stores of vitamin B12. It will miss problems with B12 transport protein deficiencies. Note that it is a measure of reserves not what is actively circulating in the blood stream and available to the cells.
Many doctors still rely on blood B12 levels and blood counts.
True. Serum B12 levels along wit MMA or
Homocysteine give reliable data. I prefer
homocysteine over MMA simply because the test is simple,
reliable , reproducible and cheap.
These are not adequate, especially in vegans.
Not true….vegans are no different from anyone else as far
as testing is concerned. See answer above .
I hope this helps
Regards
Dr Bevan Hokin PhD
DIRECTOR OF PATHOLOGY
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