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.
- 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).