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How do you feel if your vitamin B12 is low?

Vitamin B12 is an essential nutrient that plays many critical roles in the body. It is involved in red blood cell formation, cell metabolism, nerve function, and DNA synthesis and regulation. Low levels of vitamin B12 can cause a variety of symptoms that range from mild to severe. In this article, we will explore the importance of vitamin B12, the causes and risk factors for deficiency, the signs and symptoms associated with low B12 levels, and how to prevent and treat a deficiency.

What is Vitamin B12?

Vitamin B12, also known as cobalamin, is a water-soluble vitamin that is naturally present in some foods and available as a dietary supplement. It helps keep the body’s nerve and blood cells healthy and helps make DNA. Vitamin B12 is bound to protein in the food we eat. Hydrochloric acid in the stomach releases B12 from proteins during digestion. Once released, vitamin B12 combines with a protein made by the stomach called intrinsic factor and is absorbed by the body.

Some key facts about vitamin B12:

  • It helps make red blood cells and keeps the nervous system working properly
  • It plays a role in metabolizing every cell in the human body
  • It may boost mood, energy, concentration and memory
  • It may help prevent megaloblastic anemia
  • It helps recycle and synthesize DNA
  • It supports a healthy pregnancy

The recommended daily intake of B12 is 2.4 mcg for ages 14 and over. The body is able to store B12 for years, so deficiency is rare in adults unless absorption is inhibited or intake is inadequate.

Causes of Vitamin B12 Deficiency

There are several reasons why someone may become deficient in vitamin B12:

Inadequate Intake

Since B12 is only found naturally in animal foods, vegetarians and vegans are at a higher risk of deficiency if they do not properly supplement. The elderly are also prone to inadequate intake due to reduced appetite.


Even if one is consuming enough B12, certain conditions can affect the body’s ability to absorb the vitamin. These include:

  • Pernicious anemia: An autoimmune disease that destroys stomach cells that produce intrinsic factor needed for B12 absorption.
  • Surgery affecting the stomach or intestines: Such as gastric bypass, which reduce the stomach’s surface area.
  • Medications: Including antacids, metformin and proton pump inhibitors.
  • Pancreatic insufficiency: Reduced pancreatic enzymes also impede absorption.
  • Alcohol abuse: Long-term heavy drinking can damage the lining of the stomach and small intestine.
  • GI disorders: conditions like Crohn’s disease or celiac disease that affect nutrient absorption.

Other Causes

In rare cases, an inherited condition can reduce B12 absorption. Infection with certain parasites can also contribute to vitamin B12 deficiency.

Risk Factors

The following groups are at an increased risk of developing a vitamin B12 deficiency:

  • Older adults: Around 10-30% of adults over age 50 have low B12 levels from reduced intake and absorption.
  • Vegetarians and vegans: Plant foods have no vitamin B12 unless fortified. Vegans are at highest risk.
  • Those with stomach/intestinal disorders: e.g. celiac disease, Crohn’s disease, surgery removing parts of the stomach.
  • People taking heartburn medications: Medicines like proton pump inhibitors inhibit absorption.
  • People with pernicious anemia: Autoimmune disease prevents proper absorption.
  • Those with pancreatic insufficiency: Reduced pancreatic enzymes also impede absorption.
  • Those who abuse alcohol: Impairs the body’s ability to absorb several nutrients.

Being aware of these risk factors and mitigating them through proper dietary intake, supplementation if needed, and having blood levels checked routinely can help prevent deficiency.

Signs and Symptoms

Mild vitamin B12 deficiency may have no obvious symptoms initially. As the deficiency worsens, various symptoms can result. Potential signs of low vitamin B12 include:

Fatigue and Weakness

One of the most common complaints is fatigue, tiredness and weakness. Since vitamin B12 plays a role in producing red blood cells and transporting oxygen throughout the body, low levels can manifest as reduced energy and shortness of breath. Weakness in muscles may also occur.

Neurological Problems

Given vitamin B12’s importance for nerves and neurotransmitter signaling, deficiency can lead to:

  • Numbness and tingling in hands and feet
  • Difficulty walking or moving
  • Dizziness or vertigo
  • Vision problems or blurred vision
  • Dementia or memory loss
  • Poor concentration, focus and “brain fog”

Psychiatric Disturbances

Neuropsychiatric disturbances associated with B12 deficiency may include:

  • Depression, mood swings and irritability
  • Paranoia or mania
  • Hallucinations

Gastrointestinal Effects

Some people with pernicious anemia, a cause of B12 deficiency, may have signs like:

  • Glossitis – swollen red tongue
  • Diarrhea or constipation
  • Loss of appetite and weight loss
  • Nausea and vomiting

Pale Skin, Shortness of Breath

With severe vitamin B12 deficiency, anemia can result. This manifests as pale skin, trouble catching breath, rapid heartbeat, and lightheadedness.

Other Symptoms

Less common signs that may occur include:

  • Mouth sores
  • Hair loss
  • Menstrual problems
  • Impotence
  • Infertility

If left untreated, nerve damage can become permanent and anemia can potentially be life threatening. That’s why it’s critical to be aware of the signs of vitamin B12 deficiency and seek medical care if you are experiencing any of these symptoms.

Diagnosing Vitamin B12 Deficiency

If a vitamin B12 deficiency is suspected, a physician can check blood levels of vitamin B12. Normal blood levels are between 200-900 picograms/mL (pg/mL). The lab report will specify the exact normal range.

Levels below 200 pg/mL indicate a definite B12 deficiency. Borderline deficiency is between 200-300 pg/mL.

Doctors may also check blood levels of homocysteine and methylmalonic acid. These may be elevated when vitamin B12 levels are too low.

Other blood tests can help determine if deficiency is caused by pernicious anemia, an intestinal disorder, thyroid problems or other factors that can aid treatment.

Preventing Vitamin B12 Deficiency

Many cases of B12 deficiency can be prevented through proper daily intake from foods and/or supplements. The recommended daily amount of B12 for adults is 2.4 mcg.

You can help ensure adequate intake by:

  • Eating B12 fortified foods like cereal, milk, and nutritional yeast
  • Taking a multivitamin containing B12
  • Taking a dedicated B12 supplement
  • Getting adequate animal products if not vegetarian/vegan
  • Opting for a B12 spray for better absorption if concerned about absorption issues

Vegans have to rely on fortified foods and supplements for their vitamin B12 needs. Those with absorption conditions like pernicious anemia may need a higher dose taken sublingually or via injection to bypass the absorbed defect.

Routine screening of B12 levels is also recommended, especially in those over 50 years old. This allows detection of deficiencies before symptoms occur.

Treating Vitamin B12 Deficiency

Treatment for a vitamin B12 deficiency will depend on the severity and cause:

Mild Deficiency

If deficiency is caught early, the first line of treatment is changing dietary habits and/or B12 supplementation. Increased intake through foods high in B12, fortified foods or supplements is often adequate for correcting a mild deficiency.

Moderate/Severe Deficiency

For more significant deficiency causing neurological symptoms and/or anemia, B12 injections are usually required. An initial loading dose series will be given to get levels up quickly, followed by periodic maintenance injections.

Typical injection regimen:

  • 1,000 mcg intramuscular injection per day for one week
  • Followed by 1,000 mcg per week for one month
  • Then 1,000 mcg injections every 1-3 months for maintenance

Absorption disorders may require lifelong injections, while dietary deficiencies can be managed through diet and oral supplements once levels improve.

Other Treatments

If an underlying condition is causing deficiency, treatment will target that as well:

  • Medication changes if drugs are interfering with absorption
  • Blood transfusions for severe anemia
  • Iron supplements if iron-deficiency anemia is also present
  • Changes to pancreas enzyme or antacid medications
  • Treatment of Helicobacter pylori bacterial overgrowth if present

Proper treatment can reverse most symptoms of vitamin B12 deficiency within weeks to months. Early detection and management are key to avoid long-term complications.

The Takeaway

Vitamin B12 is an essential nutrient needed for red blood cell production, neurological function, DNA synthesis, and more. Low levels can lead to tiredness, weakness, psychiatric issues, neurological problems, anemia and other symptoms.

Risk factors for B12 deficiency include older age, gastric disorders, medications, vegetarian/vegan diets, alcohol abuse and pernicious anemia. Preventing deficiency means getting adequate B12 of 2.4 mcg/day through food and/or supplements.

Mild cases can be corrected through improved diet and supplementation. More significant deficiency requires B12 injections and sometimes additional treatment to manage an underlying absorption disorder. With proper treatment, most symptoms can be reversed.

Knowing the causes, symptoms and treatment for vitamin B12 deficiency allows quick intervention to correct this condition and avoid complications. Be alert to your individual risk and seek medical advice if any signs of deficiency arise.