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B12, Diet & health, Vitamins & minerals

What is Vitamin B12?  The Uses, Benefits, and Side Effects 

Vitamin B12 is the most complex of all vitamins and one of eight B vitamins.  It is also known as cobalamin.  It is only made by some archaea and bacteria that is either eaten or produced in some animals.  It is not produced within the human body so must be eaten, supplemented, or injected.  There are some animals that eat or produce vitamin B12 and store it in their livers and/or pass it on through their eggs or milk.  Animal food sources that contain vitamin B12 include meat such as beef (especially liver because that’s where animals store it), fish, and fowl, as well as eggs and dairy products.  Fruits and vegetables do not contain vitamin B12.  You also can find vitamin B12 in fortified foods such as breakfast cereals, nutritional yeast, energy bars and energy drinks.  Vitamin B12 can also be synthesized in the lab.  Be sure to read the labels.  Look for cyanocobalamin.  It is more easily absorbed.

The Recommended Dietary Allowance for:

  • Infants (age 0-1) = 0.4 – 0.5 mcg/day
  • children (age 1-3) = 0.9 mcg/day
  • children (age 4-8) = 1.2 mcg/day
  • children (age 9-13) = 1.8 mcg/day
  • adults (age 14+) = 2.4 mcg/day
  • pregnant = 2.6 mcg/day
  • breastfeeding = 2.8 mcg/day

As you can see, our B12 requirements are very low.  So why then do most vitamin B12 supplements contain such high doses such as 1,000 – 5,000 mcg?  It’s because the vitamin B12 binds to the protein in the foods we eat and then gets broken down (unbound from the protein) in the stomach by the hydrochloric acid. From there, vitamin B12 combines with a protein called intrinsic factor so that it can be absorbed further down in the small intestine.  The high doses of vitamin B12 found in most supplements are not the amount that will be absorbed.  There needs to be an adequate amount of intrinsic factor (IF) as well.  Intrinsic factor is a protein produced by the parietal cells located in the gastric body (the largest section of your stomach) and fundus (the upper part of the stomach) and plays a crucial role in the transportation and absorption of vitamin B12 by the terminal ileum.  Intrinsic factor binds to vitamin B12 in the stomach and then travels to the intestines to be absorbed into the bloodstream.  Some people do not make enough intrinsic factor or have a condition that destroys it.  If your body does not make enough intrinsic factor, you can develop a type of vitamin B12 deficiency called pernicious anemia.  Surgical removal or bypass of the stomach and certain other health conditions can also cause you to stop making intrinsic factor.  Adults 50 and over may need to take supplements or eat fortified foods because as you age, the acidity of your stomach acid declines, and you may not be able to break down and absorb vitamin B12 as much as you used to.

Vitamin B12 is used by the body for:

  • produce DNA (fatty acid and amino acid metabolism),
  • normal functioning of the nervous system (synthesis of myelin), and
  • the circulatory system (maturation of red blood cells in the bone marrow). 

A deficiency of vitamin B12 can lead to severe and irreversible damage especially to the brain and/or nervous system.  The signs and symptoms of a vitamin B12 deficiency are:

  • tiredness, weakness, fatigue
  • headache, lightheadedness
  • breathlessness
  • loss of appetite
  • severe joint pain
  • brain fog, memory problems
  • depression, mania, and psychosis
  • reduced fertility           
  • pins and needles sensations, neuropathy and
  • pernicious anemia (an autoimmune, blood disorder with decreased red blood cell (RBC) production)

Pernicious anemia can lead to:

  • Gastrointestinal (GI) problems such as altered bowel motility (mild diarrhea or constipation)
  • Loss of bladder or bowel control
  • Gastric antral vascular ectasia (watermelon stomach)
  • Neurological problems such as sensory or motor deficiencies (absent reflexes and/or diminished vibration or soft touch sensation)
  • Subacute combined degeneration of the spinal cord

There is no gold standard way to test for a vitamin B12 deficiency.  Most doctors do not test for it unless there are some signs and symptoms.  If you do have signs and symptoms, be sure to ask your doctor to do a complete blood count (CBC).  The complete blood count (CBC) with differential is one of the most common laboratory tests performed today.  It gives information about the production of all blood cells and identifies your oxygen-carrying capacity through the evaluation of your red blood cell (RBC) indices, hemoglobin, and hematocrit.  It also provides information about your immune system through the evaluation of the white blood cell (WBC) count.  When you get your blood test back, it will list a range of components such as WBC (white blood cell count), RBC (red blood cell count), Hemoglobin, Hematocrit, and more.  It also will list your values and the standard range as well as a flag if it is too high or too low.  Your doctor will discuss the results with you.  This test is helpful in diagnosing anemia, infections, acute hemorrhagic states, allergies, and immunodeficiencies but it is possible that blood serum levels of vitamin B12 can be maintained and still appear normal while your stores are being depleted.  Further testing may be necessary.

Who is at Risk of a Vitamin B12 Deficiency?  Vegetarians, vegans, adults over 75, and people that have had gastric or small intestine resections, inflammatory bowel disease, or have used metformin (a diabetes medication) for more than four months, or have used of proton pump inhibitors, histamine H2 blockers, or antacids for more than 12 months.

Interesting Facts:

Hydroxocobalamin can be injected intramuscularly to treat Vitamin B12 deficiency but can also be injected intravenously for the purpose of treating cyanide poisoning.  The hydroxyl group is displaced by cyanide, creating a nontoxic cyanocobalamin that is excreted in the urine.

The B vitamins may help detox the liver of cannabinoids.


Institute of Medicine (US) Standing Committee on the Scientific Evaluation of Dietary Reference Intakes and its Panel on Folate, Other B Vitamins, and Choline. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington (DC): National Academies Press (US); 1998. 9, Vitamin B12. Available from:

Harvard School of Health, Nutrition Source, Vitamin B12.  Available at

National Library of Medicine, MedLine Plus, Intrinsic Factor.  Available at

Al-Awami HM, Raja A, Soos MP. Physiology, Gastric Intrinsic Factor. [Updated 2021 Jul 22]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from:

American Family Physicians.  ROBERT C. LANGAN, MD, FAAFP, and ANDREW J. GOODBRED, MD, St. Luke’s Family Medicine Residency Program, Bethlehem, Pennsylvania.  Vitamin B12 Deficiency: Recognition and Management. September 15, 2017.  Available at,serum%20vitamin%20B12%20level.&text=A%20serum%20methylmalonic%20acid%20level,is%20normal%20or%20low%2Dnormal.

Mayo Clinic.  Complete Blood Count.  Available at,blood%20cells%2C%20which%20carry%20oxygen

Good Rx Health.  Acid Reflux Medicine: Antacids vs. H2 Blockers vs. Proton Pump Inhibitors, What’s Best for Heartburn Relief? Amy B. Gragnolati, PharmD, BCPS, Joshua Murdock, PharmD. Reviewed by Joshua Murdock, PharmD. Updated on March 11, 2022. Available at

Green Flower Media “How to Detox from Cannabis” available at