Private Medicine · Women’s Health

Vitamin B12 Deficiency — Symptoms, Causes, and Testing

Fatigue, tingling, poor concentration: vitamin B12 plays a role in many complaints, but it’s often measured the wrong way. What Holo-transcobalamin and MMA actually tell you — and when supplementation makes sense.

Reading time3 minClinical overview with references.
BasisMedical literatureGuidelines and consensus papers.
Last updatedAugust 2026Revised as new evidence emerges.

Knowledge Base · Nutrients

Symptoms, Causes, Testing

Vitamin B12 is involved in blood formation, nerve function, and energy metabolism. A deficiency often develops gradually and first shows up as something nonspecific — fatigue, poor concentration, or tingling. This overview shows who is affected, which values are meaningful, and when supplementation is really worthwhile.

Medical overview · Dr. med. Thomas Ackermann · Specialist in Anesthesiology

What vitamin B12 does in the body

Vitamin B12 contributes to normal energy metabolism, normal function of the nervous system, and normal formation of red blood cells — and it contributes to the reduction of tiredness and fatigue. The body cannot make B12 itself and can only store limited amounts; it is absorbed from food through a specialized mechanism in the gastrointestinal tract. If something goes wrong at any point — intake or absorption — a deficiency develops over months to years.

Typical signs

Symptoms are nonspecific and overlap with other causes of persistent fatigue:

  • Fatigue, exhaustion, and reduced stamina
  • Concentration and memory problems
  • Tingling, numbness, or a “fuzzy” feeling in hands and feet
  • Paleness as a possible sign of anemia
  • Burning tongue or changes to the mucous membranes

Who is particularly at risk

Vegan and vegetarian diets

Vitamin B12 occurs almost exclusively in animal foods. On a fully plant-based diet, taking a supplement is generally necessary.

Older age

Absorption capacity in the stomach declines with age — a deficiency can then develop even with adequate intake.

Gastrointestinal conditions

Atrophic gastritis, pernicious anemia, inflammatory bowel disease, or stomach surgery can impair absorption.

Certain medications

Metformin and acid-reducing medications (proton pump inhibitors) can reduce B12 absorption over time.

Which blood values are meaningful

A single total value is often not enough — especially in the early stage, it can still be within the normal range. It’s best to assess the values in context:

Value What it shows
Total vitamin B12 Screening test; can still be within the normal range in an early deficiency.
Holo-transcobalamin The “active” form of B12 — drops earlier than the total value.
Methylmalonic acid (MMA) A functional marker; rises when too little B12 is actually reaching the cells.
Blood count (MCV) Enlarged red blood cells can point to a macrocytic anemia.

Folate is often measured alongside B12, since deficiencies in both look similar and influence one another.

More is not better. High-dose B12 without a proven deficiency doesn’t give you an extra energy boost. The blood value normalizes — a benefit beyond that is not supported by evidence. Supplementation makes sense with a proven or anticipated deficiency, not as a blanket “energy remedy.”

When supplementation makes sense

With a proven deficiency, B12 is replaced — usually as a tablet, which is sufficient for most people. An injection makes particular sense when absorption through the gut is impaired (for example with pernicious anemia or after stomach surgery), or with a severe deficiency. On a fully plant-based diet, ongoing preventive supplementation makes sense. Which form, dose, and duration suit you depends on your results.

Always tired? An overview of the causesIron calculatorIron deficiency overview

Get your B12 and fatigue checked

Whether a B12 deficiency is behind your fatigue — or something else is — can only be clarified through history-taking, examination, and targeted diagnostics. That is exactly what the Exhaustion and Nutrient Check covers.

To the Exhaustion and Nutrient Check

This article is for general information and to help you prepare for a medical consultation. It does not replace individual advice, an examination, a diagnosis, or treatment. Whether, and in what form, supplementation makes sense can only be judged after your results are known. Medical disclosure under German law (§630e BGB) takes place exclusively in a personal consultation.

Dr. med. Thomas Ackermann

Dr. med. Thomas Ackermann
Specialist in Anesthesiology · Harmonie der Ästhetik, Herzogenaurach. Evidence, not promises.

Based in part on EFSA health claims for vitamin B12 (Regulation (EU) No. 432/2012) and assessments by the German Nutrition Society (DGE). Information provided without claim to completeness.

Next step

Questions about this topic?

What applies to you is best discussed in person — with your results, without time pressure. Herzogenaurach, twelve minutes by car from Erlangen.