The burning starts at night — what's actually happening to the nerves in your feet

Pins and needles by the afternoon. A burning that shows up the moment the house goes quiet. Socks you can't feel. It is one of the most common reasons people over 55 end up at the doctor, and the explanation is more specific than "getting older."

Why the feet, and why at night

The nerves running to your feet are the longest in the body — a single fiber travels from the base of the spine to the tip of a toe, and has to be supplied the whole way. When anything interferes with that supply, the far end goes first. That is why symptoms start in the toes and work upward, almost always in both feet.

The night part is not your imagination. During the day, movement and ordinary noise from other senses crowd the signal out. In bed there is nothing competing, and the misfiring nerve has the floor to itself.

The most common cause by far is diabetes, including blood sugar that has been creeping up for years without a diagnosis. But it is not the only one — and some of the other causes are correctable.

The deficiency that hides behind the diagnosis

Metformin, the most widely prescribed drug for type 2 diabetes, interferes with the absorption of vitamin B12. Over years of use, levels can fall far enough to cause a deficiency — and B12 deficiency causes peripheral neuropathy on its own, with symptoms that are close to identical.¹

So it is entirely possible to have both at once: nerve damage from diabetes, plus nerve damage from a deficiency caused by the drug treating it — with the second written off as more of the first. B12 deficiency is described in the medical literature as underdiagnosed, partly because nobody thinks to check.²

If you take metformin and have symptoms in your feet, ask your doctor for a B12 test. It is a simple blood test, and if that is what is going on, it is treatable.

What the evidence says about the nutrients — honestly

Several nutrients get sold for nerve health. Some have been studied properly, and the results are more mixed than the marketing suggests. What follows is about the nutrients themselves — always check the label of any product you are considering to see what it actually contains, and in what amounts.

• Alpha-lipoic acid The most studied of the group, including a Cochrane systematic review.^3,4 Reviewers have been cautious: trials vary in quality and the effect is modest where it is found. It is not a cure and no serious source presents it as one. Also occurs naturally in spinach, broccoli and organ meat.
• Benfotiamine A fat-soluble form of vitamin B1.⁴ The mechanistic rationale is better established than the clinical proof. Thiamine comes mainly from whole grains, pork and legumes.
• Vitamin B12 The clearest case, but only for people who are actually low. If you are not deficient, extra B12 does not do anything for nerve pain.^1,2 The only vitamin built around a metal atom — cobalt, at the centre.
• Acetyl-L-carnitine Assessed in a meta-analysis of randomized trials in peripheral neuropathic pain.⁵ Studied, some signal, not conclusive. Carnitine's known job is carrying fatty acids into the mitochondria.