B12: THE COMPLEX VITAMIN
Vitamin B12, or cobalamin, is the
largest and most structurally complex of all of the vitamins. It’s
essential for the development of red blood cells, normal growth, and
nervous system maintenance. Our primary sources are animal products
(meats, dairy, poultry, eggs and seafood) because it is only synthesized
by microorganisms (bacteria and archaea), some of which are found in
the soil around the grasses/weeds animals eat.
How much do we need? The Recommended Dietary Intake
(Recommended Dietary Allowance in North America) of 2.4 micrograms per
day for women and men is relatively small, as B12 is concentrated and
stored in the liver (3000–5000 micrograms in the average liver),
secreted in bile and reabsorbed in the terminal ileum (small intestine).
To put this into perspective, if you don’t consume any B12, the
supplies in the liver will typically last a healthy adult several years.
Vitamin B12 deficiency
Symptoms can be gradual, non-specific and subtle, so deficiency is hard
to recognise. Milder symptoms such as weakness, tiredness, and memory
loss can occur before true deficiency develops. True deficiency leads to
serious health problems including megaloblastic anaemia (unusually
large, structurally abnormal, immature red blood cells), paralysis,
dementia, fatigue, and mood disturbances. If left untreated, serious
neurological and neuropsychiatric complications can occur. Vitamin B12
deficiency has also been linked with an increased risk of heart attack
and stroke.
True vegans, who are at risk of developing
B12 deficiency because animal foods are off the menu, should make sure
they consume B12-fortified foods such as some soy milks, or
yeast-products where the yeast has been grown in a B12-fortified medium.
Alternatively, they should take a B12 supplement (preferably chewable).
But
they are not the only group of people at risk. In fact, the most common
cause of B12 deficiency is autoimmune pernicious anaemia, where
absorption is impaired due to intrinsic factor deficiency arising from
autoimmune destruction of parietal cells in the stomach. Other common
causes of B12 deficiency include gastrectomy (gastric surgery), ileal
(small intestine) resection, pancreatic insufficiency, and malabsorption
syndromes including Crohn’s disease and coeliac disease. Other less
common causes of B12 deficiency include use of drugs such as biguanides
(metformin), antacids, antibiotics and colchicines (used to treat gout),
and rarely, malabsorption due to gastrointestinal bacterial overgrowth,
congenital defects (e.g. birth transcobalamin deficiency), and
infestation. Pure nutritional deficiency is rare and usually occurs only
in strict vegans.
The incidence of vitamin B12
deficiency increases with age, probably due to the fact that elderly
people are more likely to suffer from malabsorption. This malabsorption
is caused primarily by gastric atrophy but also by chronic carriage of
Helicobacter pylori (the bacteria that causes stomach ulcers), long-term
ingestion of metformin and certain antacids, and increased chances of
having gastric surgery. As well as varying with age, prevalence also
varies with gender: elderly men are more likely to have low B12 levels
than elderly women.
People with type 2 diabetes or
polycystic ovarian syndrome who are treated with biguanides (metformin)
may become deficient in B12. Metformin-induced B12 malabsorption may be
due to digestive changes, which leads to the binding of B12-intrinsic
factor complex. If you have been taking metformin for a prolonged period
of time, ask your doctor to check your B12 status.
Commonly
used antacid medications for gastrointestinal problems relating to
excessive acid production include proton pump inhibitors and histamine
2-receptor antagonists. Common conditions that may require the use of
antacids include peptic ulcer diseases, oesophagitis, gastro-oesophageal
reflux diseases and Zollinger-Ellison syndrome. Antacid use is related
to vitamin B12 deficiency in two ways. First, by lowering gastric
acidity, it interferes with vitamin B12 absorption as vitamin B12 cannot
be unbound from dietary protein in the stomach. Second, a higher pH
creates an environment that promotes bacterial overgrowth in the
intestine impairing the absorption process.
If you think you might be deficient in B12, consult your doctor.
Read more:
- NHMRC. Vitamin B12
- Association between metformin and vitamin B12 deficiency in patients with type 2 diabetes: A systematic review and meta-analysis
- Association between vitamin B12 deficiency and long-term use of acid-lowering agents: a systematic review and meta-analysis
Alan Barclay, PhD is a consultant dietitian and chef (Cert III). He worked for Diabetes Australia (NSW) from 1998–2014 . He is author/co-author of more than 30 scientific publications, and author/co-author of The good Carbs Cookbook (Murdoch Books), Reversing Diabetes (Murdoch Books), The Low GI Diet: Managing Type 2 Diabetes (Hachette Australia) and The Ultimate Guide to Sugars and Sweeteners (The Experiment, New York).
Contact: You can follow him on Twitter or check out his website.
