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Always tired? foggy head? Could you be deficient in Vitamin B12?

Updated: Nov 16, 2021

Is it estimated that as many as 40% of the population have low plasma B12 levels at a level in which neurological issues begin to manifest. Unfortunately, vitamin B12 levels are not routinely tested and the reference range of what is considered low (which is 200 pg/mL - 350 pg/mL in most countries) is too low so many people who are tested are considered normal even with clear B12 deficiency symptoms. Plasma levels below 500 - 550 pg/mL have been associated with neurological, psychological, and cognitive decline which is why in places like Europe and Japan this is their low reference range.

Vitamin B12 is an essential nutrient. It works together with folate in the synthesis of DNA and red blood cells, it helps to regulate brain activity and is involved in the production of the myelin sheath around the nerves and the conduction of nerve impulses.

It is also important for methylation an important liver detoxification pathway. If B12 levels are low homocysteine levels can be elevated.

The following diseases have been associated with vitamin B12 deficiency:

Alzheimer’s, dementia, memory loss, multiple sclerosis (MS)

  • Depression, anxiety, bipolar disorder, psychosis

  • Alzheimer's, dementia, memory loss, multiple sclerosis (MS)

  • Cardiovascular disease (due to high homocysteine levels)

  • Autism, ADHD, ADD, dyslexia, and other learning and behavioural issues

  • Autoimmune disease

  • Inflammatory bowel disease (Crohn's disease, Ulcerative Colitis, Celiac disease)

  • Infertility and recurring miscarriage

Vitamin B12 is found mainly in animal foods such as meat, fish, dairy products, and eggs however, even if you are eating meat a few times a day you can still become deficient if your body is unable to absorb it. Vitamin B12 can also be manufactured by our gut bacteria in the intestines although there is no evidence of how well absorbed or utilised this is.

The absorption process of vitamin B12 is complex and ` Uptake depends on gastric parietal cells excreting hydrochloric acid, intrinsic factor, and pepsin. Pancreatic enzymes and receptors in the distal ileum must be present along with the blood protein transcobalamin II to process B12. Lastly, the liver converts B12 to the active forms adenosylcobalamin and methylcobalamin for utililzation' (Pacholok, 2013)

A deficiency of intrinsic factor, which is required for vitamin B12 to be absorbed in the intestines is a common reason vitamin B12 from food is not absorbed very well. Intrinsic factor is a mucoprotein enzyme produced by the parietal cells of the stomach (which also make hydrochloric acid). Any problems with the stomach, as well as stress, inflammation, allergies, and aging, can reduce the production of hydrochloric acid and intrinsic factor. So for vitamin B12 to be absorbed a person must have a healthy, efficient digestive system. Some of the most common causes of vitamin B12 malabsorption are:

  • Leaky gut and inflammatory bowel disease

  • Gut dysbiosis (imbalance in gut bacteria)

  • Low stomach acid (hypochlorhydria)

  • The autoimmune condition pernicious anemia - as the body attacks and destroys intrinsic factor the protein that is essential for B12 absorption.

  • Acid suppressant medications

  • Excessive alcohol

  • Vegan or vegetarian diets (plant sources are poorly absorbed)

According to various studies, 50% of long term vegetarians and 80% of vegans are extremely low in B12. According to Chris Kresser (2011), B12 is the only vitamin that contains a trace element (cobalt), which is why it’s called cobalamin. Cobalamin is produced in the gut of animals. It’s the only vitamin we can’t obtain from plants or sunlight. Plants don’t need B12 so they don’t store it. A common myth amongst vegetarians and vegans is that it’s possible to get B12 from plant sources like seaweed, fermented soy, spirulina, and brewer’s yeast. But plant foods said to contain B12 actually contain B12 analogs called cobamides that block the intake of and increase the need for true B12'.

Because vitamin B12 is stored in the body it can in some cases take about 5 years for some of the more severe symptoms to manifest. Here are the typical symptoms of B12 deficiency:

  • Weakness, fatigue, tiredness, generally feeling run down.

  • Brain fog and lightheadedness

  • Heart palpitations, shortness of breath

  • Pale skin

  • A smooth tongue

  • Lack of appetite in adults and children

  • Constipation, diarrhea, gas, bloating.

  • Numbness, tingling in extremities, muscle weakness, coordination problems

  • Mental problems such as depression, anxiety, memory loss, changes in behaviour.

  • Fertility issues and recurring early miscarriage.

So if you have any of the above symptoms it would be worth getting your B12 levels tested by your health practitioner as you may need supplementation or B12 injections for more severe cases. If you are looking to take a B12 supplement look for one that contains sublingual methylcobalamin which is the active coenzyme form of vitamin B12 that is more bioavailable than the common form cyanocobalamin. Sublingual B12 supplements in the form of methylcobalamin are available in most health shops.


Kresser C (6/5/ 2011) B12 Deficiency: a silent epidemic with serious consequences -

Pacholok S M (13/12/2013) Vitamin B12 Deficiency: Serious Consequences -

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