You probably know the feeling of running on empty for weeks on end. Most people put it down to a busy stretch or a bad night's sleep. For some, something smaller is behind it.
Vitamin B12 deficiency affects roughly 6 percent of adults under 60 and nearly 20 percent of those over 60 in the United States, according to the American Academy of Family Physicians.
Many people go undiagnosed for months. The symptoms look so much like aging, stress or ordinary tiredness that few think to check.
Vitamin B12 keeps red blood cells healthy and the nervous system working. When it runs low, the body cuts corners. The clues appear in slow, scattered ways.
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Eight signs the body may be running low on B12
1. Lasting fatigue and weakness. B12 is needed to build the red blood cells that carry oxygen. When those cells are too few or oversized, muscles and brain run short of fuel. Being tired for weeks even after rest is a classic early sign.
2. Pins and needles in the hands or feet. B12 helps keep the protective coating around nerves intact. Low levels can thin it, which the NHS lists among the common signs. The feeling is often described as tingling, numbness or a dull burn.
3. Unsteady walking or trouble with balance. The nerves running down the spinal cord slowly break down when B12 is low. The result is a wobbly, cautious gait that is easy to blame on age.
4. A sore, red or swollen tongue. Tongue cells turn over quickly and need B12 to renew. A shortage can leave the surface smooth, inflamed and painful. Doctors call this glossitis.
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5. Recurring mouth ulcers. The same cell renewal problem hits the inside of the cheeks and lips. Painful sores keep coming back for no obvious reason.
6. Low mood, anxiety or irritability. B12 helps the body make brain chemicals that regulate mood. Low levels have been linked with depression and anxiety, and in severe cases confusion.
7. Memory lapses and brain fog. Thinking feels slower, and simple tasks take more effort. In older adults the picture can look like early dementia, which is why guidelines flag it as a reason to test.
8. Pale skin and breathlessness on mild effort. Fewer and larger red blood cells deliver less oxygen. Climbing a flight of stairs leaves you winded, and the skin can look pale or faintly yellow.
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Who is most at risk
Older adults carry the highest risk. After about age 50 the stomach makes less acid, and acid is needed to free B12 from food. That alone can slowly tip the balance.
People on a strict plant-based diet are another core group. Vitamin B12 sits almost only in animal foods, so vegans and strict vegetarians who skip fortified foods or a supplement often fall short.
Metformin, the standard first-line drug for type 2 diabetes, lowers B12 absorption over time. A 2025 scoping review in BMJ Open reports that up to 10 percent of patients taking metformin develop B12 deficiency through malabsorption.
Long-term users of acid-blocking medicines are also at risk. Proton pump inhibitors and H2 blockers reduce stomach acid, and that can quietly lower B12 levels, especially in older users.
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Pernicious anemia, an autoimmune condition that destroys a protein the gut needs to absorb B12, and stomach or bowel surgery can leave people short regardless of what they eat.
A simple blood test gives a clear answer
Vitamin B12 is measured with a standard blood test. If the result sits in a gray zone, doctors can add a methylmalonic acid test, which rises when B12 is truly running low.
Treatment usually works. High-dose B12 tablets or injections restore levels, and oral replacement at 1 to 2 milligrams a day has matched injections in trials for correcting anemia and nerve symptoms.
People with pernicious anemia or severe nerve damage are typically started on injections. Anyone with ongoing symptoms and one of these risk factors can ask their doctor for a B12 blood test.
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This article is made and published by Mie Hermansen, who may have used AI in the preparation.