Vitamin B12 Deficiency Symptoms Can Range Far Beyond Fatigue

Vitamin B12 plays crucial roles in maintaining the health of your blood cells, digestive system, brain, and nervous system.

Woman taking supplements for her vitamin b12 deficiency symptoms

Vitamin B12 supplements may contain a few different forms of the vitamin.

© Alex Kalmbach |

Vitamin B12 is best known—and most promoted—as a cure for fatigue, but this vitamin is important for much more than keeping energy levels up. Vitamin B12 deficiency symptoms include everything from depression, fatigue, and memory loss to canker sores and dizziness.

Vitamin B12 plays crucial roles in maintaining the health of your blood cells, digestive system, brain, and nervous system. And while fatigue due to anemia is sometimes a symptom, recent research shows that many people have vitamin B12 deficiency without anemia or significant fatigue. Instead, they have vitamin B12 deficiency symptoms that are more related to impairments in the nervous system.

Low Vitamin B12 Symptoms: Most Often Caused by an Impaired Nervous System

In the nervous system, vitamin B12 is necessary for the formation of myelin, a whitish insulating sheath around nerve fibers that increases the speed at which impulses are conducted. It is also needed for the production of some neurotransmitters.

Vitamin B12 deficiency, therefore, results in defective myelin synthesis and neurotransmitter imbalances, leading to a host of mental, emotional, and physical symptoms related to the nervous system.

The most common symptoms of low vitamin B12 include:

  • Abnormal sensation, typically numbness, tingling or pricking (“pins and needles”) of the lower legs and feet (both sides)
  • Weakness in the legs
  • Increased risk of falling
  • Dizziness
  • Memory loss
  • Attention deficits
  • Irritability
  • Depression
  • Mania
  • Psychosis (suspiciousness, persecutory or religious delusions, auditory and visual hallucinations and disorganized thought processes)
  • Sore, swollen, beefy red tongue
  • Sores at the corners of the mouth
  • Recurrent canker sores
  • Burning sensation of the mouth
  • Fatigue
  • Shortness of breath on exertion
  • Decreased bone health and increased risk of fracture
  • Mild diarrhea or constipation
  • Impaired vision
  • Possible increased risk of cardiovascular disease
  • Possible increased risk of cancer
  • Lightheadedness or fainting, possibly accompanied by a rapid increase in heartbeat, after standing up from a lying down position

Causes of Low B12

What causes vitamin B12 deficiency? Not eating animal products, not making enough stomach acid (hypochlorhydria, common with aging), an autoimmune disorder called pernicious anemia, and certain medications, especially acid-blocking medications (proton pump inhibitors and H2 blockers) for GERD and acid reflux, and metformin for diabetes.

Treating Vitamin B12 Deficiency Symptoms

Treatment for vitamin B12 deficiency usually starts with B12 injections. Some patients need regular injections for life, depending on the cause of the deficiency. After vitamin B12 shots have returned the body’s levels to normal, it’s possible to switch to oral vitamin B12 supplements.

A Vitamin B12 supplement may contain a few different forms of the vitamin, including cyanocobalamin, methylcobalamin, hydroxocobalamin, and adenosylcobalamin. While all these forms are capable of treating vitamin B2 deficiency, methylcobalamin is superior for oral use. The typical recommended dose for treating vitamin B12 deficiency is 2,000 micrograms per day.

For information on food sources of vitamin B12, see “The Top B12 Foods for Every Diet,” where you’ll find information on the best dietary sources of vitamin B12 for meat-eaters, vegetarians, and vegans alike. See also our posts “Vitamin B12 Shots May Provide Benefits for Chronic Fatigue” and “B Vitamins for Memory: Niacin Benefits for Alzheimer’s Disease.”

If you’re on a gluten-free diet, see Defend Against Deficiency: Celiacs’ Guide to Vitamins and Minerals at Gluten Free & More‘s website.

Share Your Experience with Vitamin B12 Deficiencies

Do you have a vitamin B12 deficiency? Or have you treated it in the past? What strategies work best for you?


Does following a vegan diet leave you with vitamin B12 deficiency symptoms? It’s something to consider, experts say. After all, fish, meat, poultry, eggs, and dairy products—all foods not included in a vegan diet—are classic sources of vitamin B12. So it’s a good idea to have your B12 levels checked when you have your annual blood work done. Very low levels may suggest you need monthly or bi-weekly B12 injections to restore and maintain healthy levels.

Vitamin B12 is essential for healthy functioning of your brain, nervous system, and metabolism. Vitamin B12 deficiency symptoms may include:

    • Fatigue and muscle weakness and even such alarming symptoms as heart palpitations and shortness of breath.
    • Nerve problems such as numbness and tingling, especially in your hands and feet. These symptoms may even affect your ability to walk properly.
    • Changes in the way your tongue looks. It may become smoother but swollen.
    • Changes in your skin’s appearance; it may become pale or jaundiced.
    • Emotions and your thinking. People with low B12 levels often complain of memory problems and depressive symptoms. If left untreated, B12 deficiency can lead to serious brain issues and other neurological problems.

Without a blood test to confirm the problem, you may not even know that you have vitamin B12 deficiency, according to the March 2017 issue of Women’s Nutrition Connection. A doctor may recognize the possibility of B12 deficiency based on a physical exam and a review of your symptoms, and a simple blood test can reveal your actual B12 levels.

This post originally appeared in 2014 and has been updated.

Nutrients. Nov 2013; 5(11): 4521–4539.


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