Vitamin B12 keeps red blood cells forming and nerves firing. When levels drop, the body sends signals that are easy to blame on a busy week or getting older.
The NIH Office of Dietary Supplements reports the deficiency affects between 1.5 and 15 percent of the general population, with older adults over-represented.
A September 2025 review in American Family Physician puts the overall US rate at roughly 2 to 3 percent, but the figure climbs sharply in specific groups. Here are the seven warning signs doctors flag most often, plus the four groups that should pay particular attention.
The seven warning signs
1. Unusual fatigue and weakness. Low B12 disrupts red blood cell production, which cuts oxygen delivery to tissues. Persistent tiredness that rest does not fix is one of the earliest symptoms the NIH lists.
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2. Tingling or numbness in the hands and feet. Neurological changes such as pins-and-needles sensations can appear before any anemia shows up on a blood test, and can become permanent if left untreated.
3. Brain fog. Trouble concentrating, forgetfulness and slower thinking are among the cognitive changes health authorities associate with low B12.
4. Mood changes. Depression, irritability and confusion count among the psychological symptoms linked to long-standing deficiency.
5. A sore, red or glossy tongue. Soreness of the mouth or tongue, sometimes called glossitis, is a well-documented sign that your mouth can reveal missing vitamins.
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6. Pale skin. Because B12 deficiency can trigger megaloblastic anemia, Cleveland Clinic lists pale skin among the physical warning signs.
7. Trouble with balance or walking. Damage to nerves in the spinal cord can affect coordination and gait, an ataxia that emerges as deficiency progresses.
Anyone noticing several of these together should ask their doctor for a blood test. A serum B12 level below 180 pg/mL is considered diagnostic in the American Family Physician review, and a methylmalonic acid test can catch borderline cases.
Who is most at risk
Adults over 60. Absorption declines with age. Atrophic gastritis, a condition affecting 10 to 30 percent of older adults, cuts the stomach acid needed to release B12 from food, the NIH notes. The Institute of Medicine recommends that adults over 50 get most of their B12 from supplements or fortified foods.
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Vegans and strict vegetarians. B12 is found almost exclusively in animal products, so those avoiding meat, fish, dairy and eggs need fortified foods or a supplement to reach the 2.4 mcg daily amount set for adults.
Metformin users. The widely prescribed diabetes drug can interfere with B12 uptake in the small intestine. Small studies suggest 10 to 30 percent of people on long-term metformin have reduced absorption, and the American Family Physician review cites a trial in which 19.1 percent of metformin-treated patients had low or borderline B12, compared with 9.5 percent on placebo.
Long-term users of acid-suppressing drugs. Proton pump inhibitors like omeprazole (Prilosec) and lansoprazole (Prevacid), plus H2 blockers such as famotidine (Pepcid), cut the stomach acid that releases B12 from food. The NIH advises monitoring B12 status in patients on these drugs for prolonged periods.
Correcting a deficiency
Once deficiency is confirmed, treatment is usually simple. High-dose oral supplements often work as well as B12 injections in most patients, according to the American Family Physician review.
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Anyone with symptoms should still speak with a doctor before starting a supplement on their own. Neurologic damage from prolonged deficiency can become permanent if the underlying cause is not addressed.
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This article is made and published by Jesper Bengtson, who may have used AI in the preparation.