Am I B12 Deficient? Take the 2-Minute Symptom Quiz

Based on NIH Office of Dietary Supplements guidance · Last reviewed: July 15, 2026 · How we source our content

B12 deficiency is a slow-motion problem. Your liver holds a two-to-five-year reserve, so you can stop absorbing the vitamin today and feel perfectly normal for a very long time — right up until you don't. That long fuse is exactly what makes it worth checking before symptoms become serious, because the late ones involve your nerves, and nerve damage doesn't always undo.

How a B12 deficiency typically unfolds

Most deficiencies follow a recognizable progression. Where you are on this timeline matters a lot for how urgent testing is:

1. Nothing at all. Stores are dropping but still sufficient. This stage can last years — it's where many long-term vegans and metformin users sit without knowing it.
2. The vague stage. Persistent fatigue and weakness, paler skin, feeling winded on stairs, low mood or irritability. Easily blamed on work, age or sleep.
3. The distinctive stage. Signs that point more specifically at B12: a sore, smooth, beefy-red tongue (glossitis), mouth ulcers, and tingling or pins-and-needles in the hands and feet.
4. The neurological stage. Numbness, balance problems and unsteady walking, memory trouble and confusion. At this point treatment is urgent — some of these changes can become permanent if the deficiency continues.

One important wrinkle: the neurological symptoms can arrive before any anemia shows up on a routine blood count. Feeling "off" with a normal hemoglobin result doesn't rule B12 out.

The five groups who should actively check

B12 is only found naturally in animal foods, and absorbing it requires stomach acid and a protein called intrinsic factor. Almost everyone who becomes deficient has a problem with one of those two things — supply or absorption:

• Vegans and vegetarians — no animal foods means no natural B12 supply. Fortified foods or a supplement aren't optional long-term; they're essential.
• Adults over 65 — up to a third of older adults produce too little stomach acid to free B12 from food, even while absorbing supplement B12 just fine.
• People on metformin — the common diabetes drug measurably lowers B12 absorption over time.
• Long-term users of acid reducers — daily PPIs (omeprazole, esomeprazole) or H2 blockers reduce the stomach acid B12 absorption depends on.
• Anyone with a gut or stomach condition — pernicious anemia, Crohn's disease, celiac disease, or previous stomach/intestinal surgery.

Testing, and where a symptom quiz fits

If you see a doctor, the usual first step is a serum B12 blood test, sometimes followed by methylmalonic acid (MMA) or homocysteine tests when the first result sits in the ambiguous middle zone. Treatment is refreshingly simple: high-dose oral B12 or injections, and the supplement form is absorbed even by most people whose problem is food-bound absorption.

Our free assessment sits one step before the blood draw. It cross-references your symptoms with your diet, age and medication profile — and just as importantly, it checks whether your symptoms actually fit a different deficiency better. Fatigue plus pale skin could be B12, but it's more often iron; tiredness with low winter mood points more toward vitamin D. Two minutes of questions is a cheap way to aim the right test at the right problem.

Frequently asked questions