Vitamin B12: why it can take years to show up

Vitamin B12 is needed to produce DNA, and so affects most bodily processes — particularly the production of red blood cells, and maintaining a healthy nervous system by contributing to the myelin sheath that insulates nerves. What follows is drawn from a piece by Carol Katté, a stoma nurse with the Ileostomy & Internal Pouch Association.

It is absorbed by the last section of the small intestine, the terminal ileum. That places people who have had surgery on that area — including formation of an ileostomy — and people with Crohn’s disease, which particularly affects it, at risk of low levels.

What deficiency feels like

• weakness, fatigue, lack of energy
• heart palpitations, shortness of breath, dizziness
• pale or yellowish skin
• a sore tongue — smooth, red or swollen
• mouth ulcers
• numbness, pins and needles, muscle pain
• changes to balance and co-ordination of movement
• blurred or disturbed vision
• problems with memory — “brain fog” — and confusion
• mood changes, depression

Other risk factors listed are age, some diabetes medication such as metformin, and some antacids taken for heartburn — the PPIs, such as omeprazole. These symptoms may be present in conditions other than B12 deficiency, which is worth saying plainly.

Why the test may not settle it

This is where it gets unusually frank: there is no ideal test, and blood tests to screen for deficiency are notoriously unreliable. The most commonly performed ones can be affected by how long blood remains in the tube before testing, and are not specific enough to separate inactive from active forms — so they may show a “normal” level the body cannot actually use. More specific tests exist in endocrinology centres, but even these are open to debate.

The conclusion is to look at symptoms alongside risk factors: if clinical features suggest deficiency, replacement therapy is important to avoid neurological impairment even if blood tests are not definitive. Intramuscular or subcutaneous injections of cyanocobalamin are described as the quickest and most efficient route, and tablets taken by mouth as not a reliable way to raise levels, because absorption is variable for the reasons above.

The routes that bypass the gut

The reason swallowed tablets disappoint is the same reason the deficiency happened: they have to be absorbed by a part of bowel that has been shortened, removed or inflamed. Two forms get around that — a spray taken under the tongue, which allows direct absorption into the bloodstream bypassing the gastrointestinal tract altogether, and a nasal spray.

Where these fit matters. It may be possible to maintain normal levels this way once the deficiency has been corrected with injections, but symptoms should be monitored carefully. The ordering is the point: the sprays are maintenance, not a way to correct a deficiency in the first place.

Food, and its limits

B12 is usually obtained from a diet containing animal products — eggs, fish, meat, dairy and poultry. People eating a vegan diet, or a vegetarian one without enough of those foods, have to get it from fortified foods or supplements.

It may also be beneficial to eat foods known to contain B12 — dairy, eggs, meat, fish, liver, poultry, fortified cereals, yeast — with the caveat that gives this whole subject its shape: for the reasons above, absorption of these is not always optimum.