Vitamin B12: why it matters and when to check your levels

Feeling tired, clumsier than usual, or dealing with pins-and-needles in your feet? Low vitamin B12 can cause those exact things. B12 helps make red blood cells, keeps nerves working, and supports energy. Most people get enough from food, but some groups don’t absorb it well or don’t eat B12-rich foods at all.

Who’s at risk and common signs

Risk factors are easy to spot: if you’re vegan or strict vegetarian, over 60, had stomach surgery, take metformin or acid blockers (PPIs), or have autoimmune gastritis (pernicious anemia), you might be low on B12. Watch for persistent fatigue, memory fog, balance problems, tingling in hands or feet, pale or inflamed tongue, and shortness of breath. Low B12 can also cause a specific type of anemia (macrocytic) and nerve damage if left untreated.

Not everyone with low B12 has obvious symptoms. That’s why testing helps. A basic serum B12 test is common, but if results are borderline your doctor may order methylmalonic acid (MMA) or homocysteine — those pick up tissue-level deficiency better.

Foods, supplements, and what actually works

Food sources: beef, liver, shellfish, fish (salmon, tuna), eggs, dairy, and fortified cereals or nutritional yeast. If you don’t eat animal products, rely on fortified foods or supplements.

Supplement forms: cyanocobalamin and methylcobalamin are the usual options. Cyanocobalamin is stable and inexpensive; methylcobalamin is often chosen when nerve support is the goal. Both raise levels. Tablets and sublinguals work for most people. Many OTC tablets contain 500–2,000 mcg because only a small fraction is absorbed by passive diffusion; even high-dose oral supplements can fix deficiency in many cases.

When to consider injections: if you have severe deficiency, neurological signs, or absorption problems (like pernicious anemia), doctors often use 1,000 mcg B12 injections to restore levels quickly, then switch to maintenance dosing.

Practical tips: get a baseline test if you’re in a risk group or have unexplained symptoms. If you take metformin or PPIs long-term, ask about periodic checks. For daily prevention, a low-dose supplement can help, but if you have symptoms choose a higher dose or follow medical advice for injections. Look for products from trusted brands and check labels for the active form.

Safety note: B12 is water-soluble and has low toxicity — overdoses are rare. Still, do a test first rather than guessing. If your energy or nerve symptoms are getting worse, see a healthcare provider promptly.

Want help picking a supplement or figuring out if you need a test? Bookmark this page and talk with your clinician — a simple blood test often clears up the mystery fast.