Vitamin B12 Deficiency Guide: Symptoms, Causes, and Treatment

Overview

Vitamin B12, also called cobalamin, is a water-soluble nutrient your body needs to make healthy red blood cells, maintain nerve function, and produce DNA. Your body cannot make B12 on its own, so you get it from animal-based foods like meat, fish, eggs, and dairy, or fortified foods and supplements. Deficiency happens when your body doesn’t get enough B12, or can’t absorb it properly, and can lead to serious health problems if not treated early.

Signs & Symptoms

Symptoms of B12 deficiency often develop slowly, so you may not notice them at first. Early signs are often related to low red blood cell count (anemia), while later symptoms affect your nerves and brain if the deficiency goes untreated.

• Fatigue, weakness, or shortness of breath with mild activity
• Pale or yellowish skin
• Numbness, tingling, or burning in your hands and feet
• Difficulty walking, balance problems, or muscle weakness
• Memory issues, confusion, or mood changes like depression
• Smooth, sore tongue or mouth ulcers
• Digestive issues like nausea, diarrhea, or loss of appetite

Causes & Risk Factors

B12 deficiency is almost always caused by either not getting enough B12 in your diet, or your body being unable to absorb the B12 you consume. Certain groups are at much higher risk of developing a deficiency:

• Older adults, who produce less stomach acid needed to release B12 from food
• People who follow vegan or strict vegetarian diets, since B12 is naturally found only in animal products
• People with gut conditions like Crohn’s disease, celiac disease, or who have had part of their stomach or small intestine removed
• People who take long-term proton pump inhibitors (PPIs) or metformin, which can reduce B12 absorption
• People with pernicious anemia, an autoimmune condition that stops your body from making intrinsic factor, a protein needed to absorb B12

Diagnosis

If your provider suspects B12 deficiency, they will start with a blood test to check your B12 levels, as well as tests for related markers like methylmalonic acid (MMA) and homocysteine, which rise when B12 is low. They may also check for anemia with a complete blood count (CBC), and test for intrinsic factor antibodies if they suspect pernicious anemia. In some cases, a bone marrow biopsy may be done to confirm megaloblastic anemia, a type of anemia caused by B12 deficiency.

Treatment & Management

Treatment depends on the cause and severity of your deficiency. For mild dietary deficiency, increasing your intake of B12-rich foods or taking over-the-counter oral supplements may be enough. For moderate to severe deficiency, or deficiency caused by malabsorption, your provider may prescribe high-dose oral supplements, or B12 injections given weekly or monthly. Most people start to feel better within a few weeks of starting treatment, though neurological symptoms may take longer to improve.

Living With B12 Deficiency

For many people, B12 deficiency requires long-term management, especially if it’s caused by an autoimmune condition or permanent gut damage. You can reduce your risk of deficiency by eating B12-rich foods if you eat animal products, or choosing fortified plant-based milks, cereals, and nutritional yeast if you follow a vegan diet. If you take medications that affect B12 absorption, talk to your provider about regular B12 level checks.