B12 and Nerve Symptoms: Tingling, Numbness and Balance

Early neurological symptoms — tingling, mild numbness, early unsteadiness — usually resolve with treatment, though it can take months. Symptoms that have been present for a long time, or that have progressed to weakness and marked balance loss, may improve only partly, and some do not improve at all: myelin can regenerate, but nerve fibers that have died do not.

The practical consequence is that B12 deficiency with nerve symptoms is treated as urgent in a way that B12 deficiency with tiredness is not. The evidence for treating promptly and adequately is strong; the evidence for what is lost by delay is stronger still. It is also why a B12 level in the "low-normal" range, in a person with nerve symptoms and a risk factor, is not reassuring: the blood level is an imperfect measure, and the main page explains why methylmalonic acid and homocysteine are checked alongside it.

The same groups as for any B12 deficiency, set out on the absorption page: people over sixty, long-term users of acid-suppressing medication or metformin, anyone who has had stomach or intestinal surgery, vegans and near-vegans, and people with autoimmune conditions of the stomach or thyroid. Two additions specific to nerves.

Nitrous oxide — "laughing gas," used in dentistry and anesthesia and increasingly recreationally — inactivates B12 directly and can produce a severe neurological deficiency within weeks in someone whose stores were already marginal. It is a recognized cause of spinal cord damage in young adults and it is worth asking about.

And a person taking large amounts of folic acid without B12 — in a fortified diet, a prenatal, or a "methylation" supplement — can have the anemia of B12 deficiency masked by the folate while the nerve damage continues. The methylation panel page covers why folate and B12 are always assessed together.

Serum B12, together with methylmalonic acid — which rises when B12 is functionally short even if the serum level looks adequate — and homocysteine. A full blood count with red-cell size. Folate. Thyroid function, blood sugar and, depending on the history, tests for the autoimmune cause of pernicious anemia. All of these are on or available through the lab-testing panel.

The point of testing before treating is that the injection would otherwise erase the evidence. A B12 shot normalizes the level within days, and a person treated blind for tingling can never afterwards find out whether B12 was the cause — or, more importantly, whether something else is.

Tingling and numbness in the feet have many causes, and B12 is one of them. Diabetes is the commonest by far. Alcohol, thyroid disease, kidney disease, some medications, spinal problems, inherited neuropathies and — rarely — conditions that need urgent treatment all produce a similar picture. A person with nerve symptoms and a low B12 has an explanation; a person with nerve symptoms and a normal B12 does not, and needs one.

We refer, before treating, when: symptoms are progressing quickly; there is weakness, not just sensation change; the symptoms are on one side or in a pattern that does not fit a length-dependent neuropathy; there are bladder or bowel changes; there is any sign of spinal cord involvement — stiffness, brisk reflexes, a marked loss of position sense; or the B12 is normal and the cause is unexplained. Those are a neurologist's assessment, and an injection given first would delay it while appearing to address it.