Signs and Side Effects of Vitamin B12 Deficiency

Exhausted woman at desk

Vitamin B12 plays important roles in your body's metabolism (converting food to energy), nervous system function, and red blood cell formation. You can meet your daily dose of B12 by eating a variety of vitamin B12-rich foods, taking supplements, or receiving injections. Doing so helps you avoid the unpleasant symptoms of deficiency.

1. Weakness and Fatigue

One of the most common B12 deficiency signs is muscle weakness and generalized fatigue. This happens because vitamin B12 deficiency causes anemia, a condition that occurs when you have too few red blood cells to carry oxygen throughout your body effectively. While there are other causes of anemia (iron, folate, and vitamin B6 deficiencies), if muscle weakness and extreme fatigue are happening to you, it's time to see a doctor to get your B12 levels checked.

2. Tingling or Numbness in Limbs

B12 deficiency can also cause your limbs (fingers, toes, hands, feet, or legs) to tingle and feel numb. This happens because of vitamin B12's role in maintaining proper nervous system function. Without sufficient vitamin B12, over time nerve damage can occur, which causes the numbness and tingling. This side effect generally happens when you've been deficient in B12 for a long time, MedlinePlus notes. Diabetes can also cause nerve disorders, so if tingling and numbness in your hands and feet happens regularly, see a doctor to determine the cause and seek appropriate treatment.

3. Shaky Movements

Are parts of your body shaky or moving without your control? Mayo Clinic suggests vitamin B12 deficiency can cause shakiness due to B12's effects on the nervous system. Shakiness is a common symptom of vitamin B12 deficiency but may not occur until you've been deficient for a while. Any time you experience uncontrolled movements or shakiness, see a doctor because other health conditions (like Parkinson's disease) can cause also this symptom.

4. Dizziness/Loss of Balance

Are you feeling dizzy or lightheaded every time you stand up? Or, do you feel unbalanced when you try to walk? This could be the result of anemia caused by vitamin B12 deficiency (due to decreases in oxygen-carrying red blood cells), and it's is a fairly common symptom of anemia. B12 injections or supplements can improve this problem, according to the American Hearing Research Foundation. Unsteadiness can be related to nerve damage in the brain's balance center.

5. Shortness of Breath

Shortness of breath, especially during physical activity, is another symptom of anemia, says the University of Maryland Medical Center. This again has to do with vitamin B12's role in oxygen-carrying red blood cell production. The Pernicious Anemia Society says shortness of breath is one of the more common symptoms of pernicious anemia (caused by B12 deficiency). However, it's also a symptom of heart disease and anemia caused by iron, B6, or folate, so have your doctor check blood levels to figure out the exact cause when experiencing shortness of breath.

6. Memory Loss, Confusion, or Difficulty Concentrating


Are you forgetful or confused, have trouble concentrating, or always feel like you're in a fog? The Pernicious Anemia Society says having "the fogs" is a common problem when you have pernicious anemia due to B12 deficiency. This has to do with vitamin B12's role in maintaining neurological brain function. However, memory problems generally only occur in cases of severe B12 deficiency, says MedlinePlus.

7. Altered Mood and Depression

Because you know B12 is necessary for proper brain function, it's probably no surprise B12 deficiency can alter your mood. You may feel depressed or irritable, says the Office of Dietary Supplements, or you may just want to be left alone often. MedlinePlus says depression generally occurs when you've had B12 deficiency anemia for quite a while. So if you're experiencing mood swings suddenly, a vitamin deficiency could be the culprit. Your mood should improve after you get your B12 (and other essential nutrient) levels back to normal.

8. Pale or Yellow Skin

Is your skin turning pale or yellowish? B12 deficiency could be the culprit, according to Harvard Health Publications. Yellowing of the skin is a B12 deficiency symptom that can often be overlooked. The Pernicious Anemia Society says pale yellow skin from B12 deficiency is usually related to abnormal liver function and isn't as common of a symptom as once thought.

9. Swollen, Red, Sore Mouth or Tongue

John Hopkins Medicine says getting too little B12 can cause your tongue to feel sore and tender. Your tongue or mouth may also become swollen or inflamed as a result of B12 deficiency. This can happen when sensory nerve damage related to B2 deficiency occurs. While a swollen, sore tongue is often thought of as a common symptom of B12 deficiency anemia, only about 10 percent of pernicious anemia sufferers experience it, says the Pernicious Anemia Society.

10. Other Potential Side Effects

Other possible side effects may occur when your body lacks sufficient vitamin B12. These include:

  • Paranoia -- A mental condition caused by neurological changes in the brain
  • Hallucinations -- Seeing things that aren't really there, caused by neurological changes
  • Low Blood Pressure -- Related to B12 deficiency anemia, says Mayo Clinic
  • Bleeding gums -- MedlinePlus says bleeding gums can happen from B12 deficiency
  • Lack of bladder or bowel control -- Mayo Clinic says this can occur during B12 deficiency
  • Vision problems -- This is related to sensory neurological changes
  • Nervousness -- This symptom can occur with mood changes
  • Constipation or diarrhea -- The University of Maryland Medical Center says this can occur during B12 deficiency
  • Loss of appetite -- John Hopkins Medicine says this can happen from B12 deficiency
  • Weight loss -- This symptom is related to loss of appetite
  • Fast heart rate -- John Hopkins Medicine reports this is a B12 deficiency symptom
  • Feeling bloated -- The Pernicious Anemia Society says this results from stomach swelling related to pernicious anemia
  • Loss of sex drive -- This symptom is related to fatigue caused by B12 deficiency anemia
  • Brittle nails -- Can occur with B12 deficiency, says the Pernicious Anemia Society
  • Burning of feet or legs -- This symptom is related to nerve damage caused by B12 deficiency
  • Pica (unusual cravings for non-food items) -- Ice cravings are common, says the Pernicious Anemia Society

How to Remedy B12 Deficiency

Most vitamin B12 deficiency symptoms can be reversed by getting B12 levels back up to normal. However, MedlinePlus says nerve damage caused by B12 deficiency can be permanent if you don't remedy the problem within 6 months after symptoms first appear. B12 deficiency treatment often includes high doses of B12 supplements or injections, depending on the cause of B12 deficiency and what your doctor recommends. If your body doesn't properly absorb vitamin B12, B12 injections may be a good fit. You should experience symptom relief within a few months of treatment (sooner in some cases).

How Much Is Enough?

The recommended dietary allowance (RDA) for vitamin B12 is 2.4 micrograms daily for adult men and women. However, if you're deficient in B12, your doctor may recommend higher doses. If your body doesn't absorb B12 properly, and high-dose vitamin B12 supplements aren't working, you might require B12 injections.

Check With Your Doctor

If you have symptoms of vitamin B12 deficiency, it's time to check in with your doctor. Since many B12 symptoms are also symptoms of other nutrient deficiencies or medical conditions, have your B12 blood levels checked to be sure.

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Signs and Side Effects of Vitamin B12 Deficiency