Vitamin B12

What it is

Vitamin B12 is not a peptide. It is a vitamin, a small molecule your body needs for nerve function, red blood cell production and DNA synthesis. You cannot make it yourself and get it from animal foods, so vegans and older adults are at higher risk of low levels.

Injectable B12 is a standard medicine for people with a proven deficiency, particularly when the problem is absorption (such as pernicious anaemia) rather than diet. In the UK the NHS uses hydroxocobalamin injections; in the US, cyanocobalamin is common. Methylcobalamin is the form most often sold in research and wellness vials.

It is popular as an energy shot. If you are not deficient, there is no good evidence it boosts energy.

History

Pernicious anaemia was fatal until the 1920s, when George Whipple, George Minot and William Murphy showed that eating liver could treat it. The vitamin itself was isolated in 1948, and Dorothy Hodgkin solved its structure in 1955.

How it works

B12 is needed as a helper (cofactor) for two enzymes: one involved in making DNA and red blood cells, and one that protects nerve coating (myelin). Without it, you can develop anaemia and nerve damage. Injection bypasses the gut, which matters when the problem is that the body cannot absorb B12 from food.

Dosage

• NHS practice for diagnosed deficiency without nerve involvement: 1 mg hydroxocobalamin IM, six times over two weeks, then every three months. With neurological symptoms, a more intensive course is used. This is guided by a clinician.
• Typical wellness doses of methylcobalamin are 1 mg (1,000 mcg), once weekly to monthly. Daily is not necessary: stores last a long time.
• If your blood level is normal, extra B12 is usually just passed in urine.
• A blood test (serum B12, with holotranscobalamin or methylmalonic acid if borderline) tells you whether you actually need it.

How it is taken

• Intramuscular injection (upper outer buttock or thigh) with a 23-25G needle is the standard medical route.
• Subcutaneous injection with a fine insulin needle also works, and many people prefer it.
• Oral and sublingual B12 can be effective even in people with poor absorption, if the dose is high enough, so injections are not always necessary.

How to reconstitute

• 10 mg vial: adding 2 ml of bacteriostatic water gives 5 mg/ml, which is 50 mcg per unit on a 1 ml syringe. A 1,000 mcg (1 mg) dose is 20 units.
• Adding 5 ml gives 2 mg/ml, or 20 mcg per unit, so 1,000 mcg is 50 units. A more dilute mix is easier to measure.
• The solution is deep red/pink. Add water gently and swirl. Keep out of light.

How it should arrive

Sealed vial with an intact cap. The powder should be a rich dark red or pink. Some products arrive as a ready-made red liquid. Pale or colourless product in a B12 vial is wrong.

How it should look once reconstituted

A clear red to pink solution with no particles or cloudiness. If it has turned brown or is cloudy, it may have degraded or become contaminated.

What to expect, and when

• In true deficiency: energy and mood may improve within days to a few weeks. Blood counts recover over weeks and nerve symptoms can take months and may not fully reverse.
• If you are not deficient, do not expect a noticeable change.
• Retest after treatment: that tells you much more than how you feel.

Side effects

• Injection-site soreness or redness.
• Mild headache, nausea, dizziness.
• Rare: itching or rash, and allergic reactions (anaphylaxis is very rare).
• Acne-like skin eruptions have been reported with high doses in some people.
• Pink or red urine is harmless and is the vitamin itself.

Risks

• The real risk is missing the cause of a deficiency. Low B12 can be due to pernicious anaemia, gut disease, or medicines such as metformin and acid blockers. It needs a diagnosis, not just a top-up.
• In people with the rare hereditary optic neuropathy (Leber's), cyanocobalamin is avoided.
• Very high levels in blood sometimes point to other conditions (liver or kidney disease, some blood disorders), so unexplained high results deserve follow-up.
• Because injections can hide anaemia from folate/B12 without fixing the cause, get tested rather than self-treating blind.
• Non-prescribed vials are unlicensed, with unknown sterility.

Potential gains

• Reversing anaemia and nerve damage caused by B12 deficiency, which is well established.
• No convincing evidence of energy, mood, weight-loss or athletic performance benefit in people with normal B12.
• Many fatigue complaints have other causes (iron, thyroid, sleep, depression), so check these as well.

Other useful information

If you think you are low, ask your GP for a blood test. The NHS provides injections for diagnosed deficiency, and if you are diagnosed, that is usually the safest and cheapest route. Vegans can usually keep levels up with regular oral supplements.