• Weakness, tiredness, or light-headedness
  • Rapid heartbeat or difficulty breathing
  • Poor memory or difficulty concentrating
  • Depression, anxiety, mania
  • Numbness and tingling of hands or feet
  • Difficulty with balance, poor coordination
  • Pale skin
  • Sore tongue
  • Easy bruising or bleeding gums
  • Upset stomach or weight loss
  • Diarrhea or constipation
  • Depression, irritability, paranoia, mania, hallucinations


If you answered “yes” to any of the above, it may be time to get tested for B12 deficiency.

Vitamin B12 is a water-soluble vitamin that is crucial to normal neurologic function, red blood cell production, and DNA synthesis. It cannot be manufactured in human beings must be regularly obtained from the ingestion of animal proteins or fortified food products.  Hydrochloric acid in the stomach liberates vitamin B12 from animal proteins.  It then combines with intrinsic factor produced by gastric parietal cells and is absorbed in the terminal ileum.

Vitamin B12 is essential to several enzymatic processes:

  1. Conversion of homocysteine to methionine
  2. Conversion of methylmalonic acid to succinyl coenzyme
  3. Conversion of 5-MTHF (methyltetrahydrofolat) to tetrahydrofolate (required for DNA Synthesis and RBC production)

How common is vitamin B12 deficiency?

B12 deficiency is common and reported to affect up to 25% of the U.S. population. Up to 20% of people over the age of 60 years old show marginal B12 status. The CDC reports, one out of every 31 Americans over 50 are B12 deficient. Sadly the current lab values of serum B12 grossly underestimate the incidence by using a cut-off range far too low. The current ranges for a common commercial laboratory, which I use are 211-946 pg/ml. Many researchers propose that we raise the lower limit of normal to 550pg/ml, which is what I use for optimal levels. In my clinical practice, I have seen many patients who have significant symptoms of low intracellular B12 and they still show “within normal range” on serum lab values. Serum homocysteine and methylmalonic acid are much more sensitive markers as they may show a deficiency earlier than serum B12.

So what causes B12 deficiency?

The main causes of B12 deficiency include inadequate dietary intake and malabsorption issues. Vitamin B12 deficiency may occur if you have certain conditions, such as:

  • Pernicious anemia, which makes it hard for your body to absorb vitamin B12 (characterized by a lack of intrinsic factor – individuals cannot properly absorb vitamin B12 in the gastrointestinal tract)
  • Atrophic gastritis or inadequate production of stomach acid (occurs in 10-30% of older adults!)
  • Helicobacter pylori infection in the stomach
  • Surgery that removed part of your stomach or small intestine including bariatric surgery (Surgical procedures in the gastrointestinal tract, such as weight loss surgery often result in a loss of cells that secrete hydrochloric acid and intrinsic factor)
  • Conditions that affect the small bowel, such as
    • Crohn’s disease
    • Celiac disease (11-41% of patients with celiac will have B12 deficiency)
    • Small intestinal bacterial overgrowth (SIBO)
    • Parasite infections, such as giardia, tapeworm
    • Chronic pancreatitis
  • Heavy alcohol use or advanced liver disease
  • Autoimmune conditions, such as Grave’s disease, Lupus
  • Malnutrition or eating disorders
  • Long term use of medications
    • Proton pump inhibitors
    • H2 blockers
    • Metformin
    • Certain antibiotics

Who should be tested for B12 deficiency?

  • Anemia with elevated MCV (mean corpuscular volume)
  • Neurological symptoms, such as numbness, tingling, difficulty with walking or balance issues
  • Changes in mental status, confusion, or disorientation
  • Dementia or Alzheimer’s disease
  • Bipolar, mania, or schizophrenia
  • Gastrointestinal disorders with malabsorption, like pancreatic insufficieny
  • Patients who have had gastrointestinal surgeries or gastric bypass
  • Anyone over age 60 years old
  • Restricted diets: vegans, vegetarians, macrobiotic diets
  • Autoimmune disorders
  • Children with autism spectrum disorders or developmental delay
  • Breast fed infants of mothers at risk
  • Eating disorders
  • Family history of pernicious anemia
  • Chronic use of PPI medications (Nexium, Prilosec, prevacid, etc) or Metformin
  • Occlusive vascular disorders (heart attack, stroke, blood clots)

Children may present differently from adults and should be tested if any of the following symptoms occur

  • Developmental delay or regression
  • Apathy or irritability
  • Weakness
  • Tremor
  • Seizures
  • Lack of coordination
  • Lack of appetite or failure to thrive
  • Poor socialization or poor motor skills
  • Speech problems or language delay
  • Anemia

You can request following blood tests from your doctor to determine if you are deficient:

  1. Serum B12
  2. Methylmalonic acid
  3. Homocysteine
  4. Complete blood counts

So what if I do have a B12 deficiency?

B12 is nontoxic and water soluble so if you are deficient the good news is it is easy to replace! Traditionally B12 has been given in the form of intramuscular injections to ensure absorption but studies have shown that sublingual forms may be equally effective. B12 may come in the form of cyanocobalamin, methylcobalamin, hydroxycobalamin, and adenoxylcobalamin. You can discuss with your doctor which form is best for you. I typically start patients with sublingual methylcobalamin in lozengers or drops at 1000-5000mcg daily. Some patients require subcutaneous or intramuscular injections, which can be taught in the office and given by the patient at home. Depending on how severe the deficiency, I will typically prescribe 5000mcg from once per month to 2-3X per week initially. Liver stores of B12 are usually repleted with a half a dozen or so doses but full repletion may take up to 20 doses. Once a patient’s symptoms are improving, maintenance of B12 may occur with as little as one injection every 2-4 weeks. There are now forms of B12 available in oral, sublingual, intranasal, transdermal and injectable forms.

Vitamin B12 can be found in large quantities in animal products, including meat, poultry, fish, seafood, eggs, and dairy products; and the consumption of these products is the most longstanding method by which human beings have taken vitamin B12 into their systems.   However, if you wish to avoid the pollutants and chemicals contained in animal food, simply take the supplements.



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