The pattern with a few signature signs

B12 shares some symptoms with iron deficiency. Extreme tiredness, a lack of energy, breathlessness. On those two alone, there is no reliable way to tell them apart without a blood test. But B12 has a handful of signs that iron deficiency does not reliably produce.

According to the NHS, symptoms of B12 or folate deficiency anaemia include:

Symptoms to watch for Pins and needles in the hands or feet. A sore and red tongue, sometimes noticeably smoother than usual. Mouth ulcers. Muscle weakness. Psychological changes ranging from mild low mood or anxiety through to problems with memory and concentration. Less commonly: changes to vision.

If most of that list is familiar and the neurological side is where it lands for you, specifically the tingling, the tongue, or the mood shifts that don't have a reason, B12 is worth looking at. Tiredness alone is not enough to point here.

"The tingling and the sore tongue are B12's signature. Iron deficiency doesn't reliably produce either."

Why B12 specifically

B12 travels almost exclusively through animal foods. Meat, fish, eggs, dairy. For most people who eat those across a week, dietary B12 is rarely the gap. A 140g salmon fillet, two medium eggs, or a 150g pot of yoghurt each contribute meaningfully to the adult target of 1.5µg a day.

The dietary risk concentrates in vegans and strict vegetarians who aren't using fortified foods or a B12 supplement. If this is you, fortified plant milks, nutritional yeast, and fortified breakfast cereals carry most of the load, and a B12 supplement fills the gap when they don't.

For people who do eat meat, fish, or dairy regularly, a dietary shortfall is less likely. When B12 is low in someone with a mixed diet, the more probable explanation is an absorption problem, not a food gap. Pernicious anaemia is the most important of these.

What B12 does in the body

Think of B12 as the ingredient your nervous system relies on to pass messages cleanly. It maintains the protective sheath around nerve fibres. Without enough of it, signals start to misfire, which is why the neurological symptoms, the pins and needles, the memory fog, the mood changes, tend to show up before or alongside the anaemia itself.

B12 also plays a role in making red blood cells. When supply is low, the body produces large, malformed red blood cells that cannot carry oxygen efficiently. The tiredness and breathlessness follow from there, the same mechanism as iron deficiency anaemia but via a different route.

The numbers

The NHS puts the adult target at 1.5µg a day. Most food labels display the EU nutrient reference value of 2.5µg, which is the figure you'll see on packaging. Both are very small targets in absolute terms. Any diet that includes meat, fish, eggs, or dairy in some quantity is likely to clear the 1.5µg bar without planning for it.

The challenge is exclusively for those who don't eat those foods, and for anyone whose gut cannot absorb B12 normally regardless of how much arrives via diet.

Animal-food sources Salmon, 140g fillet. Tinned sardines or tuna. Two medium eggs. Plain yoghurt, a 150g pot. Any meat or poultry in a typical portion.

Vegan and fortified sources Fortified plant milks (check the label, not all are). Nutritional yeast (the fortified kind). Fortified breakfast cereals. A B12 supplement if the above aren't regularly in your week.

Two distinct causes, two different routes

This is the part that matters most, and that most symptom articles skip past.

Low B12 has two meaningfully different causes, and they need different responses.

Cause and appropriate route

Dietary shortfall Not enough B12 arriving through food. Concentrated in vegans and strict vegetarians without fortified foods. Fix: fortified foods, oral supplement, or reintroducing animal foods. A blood test can confirm the level; the dietary route resolves it.

Pernicious anaemia An autoimmune condition where the immune system attacks stomach cells, blocking B12 absorption entirely. Food does not fix this. The NHS describes pernicious anaemia as the most common cause of B12 deficiency in the UK. Treatment is B12 injections, prescribed by a GP after a blood test.

If you eat animal foods regularly and the symptom pattern fits, pernicious anaemia is the more likely explanation than a dietary gap. The treatment is different: no amount of salmon or supplements will correct an absorption problem. It needs a blood test, a diagnosis, and injections.

When to see your GP

If the pattern above fits, the right next step depends on your diet.

If you eat meat, fish, eggs, or dairy most weeks and the symptoms persist, see your GP. A serum B12 blood test takes minutes and will confirm whether levels are low. If pernicious anaemia is the cause, treatment with B12 injections is straightforward and effective.

If you're vegan or strictly vegetarian and the pattern fits, start with fortified foods and a B12 supplement. If the symptoms don't ease within four to six weeks, or if they're affecting your daily life now, see your GP. A blood test is worth having at least once to establish a baseline level.

Either way, a blood test is the only way to know with certainty, and the NHS can run one. There is no reliable way to diagnose low B12 from symptoms alone.

A short, honest note

This page describes a symptom pattern. It is not a diagnosis and is not a substitute for medical advice. If what you've read here keeps fitting after a few weeks of paying attention, take it to your GP. They will run the right test and read it properly, which is the part a blog cannot do.