Always tired? foggy head? could you be deficient in vitamin B12?

Updated: Dec 17, 2019

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 is 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.

The following diseases have been associated with vitamin B12 deficiency:

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

  • Depression, anxiety, bi polar disorder, psychosis

  • Cardiovascular disease (due to high homocysteine levels)

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

  • Auto immune 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 auto immune 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 of 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 light headedness

  • Heart palpitations, shortness of breath

  • Pale skin

  • A smooth tongue

  • Lack of appetite in adults and children

  • Constipation, diarrhea, gas, bloating.

  • Numbness, tingling, 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 methycobalamin which is the active coenzyme form of vitamin B12 that is more bioavailable than the common form cyanocobalamin. In New Zealand both Source Naturals and Clinician’s have a sublingual B12 supplement in the form of methycobalamin that is 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 -

#Guthealth #vitaminb12 #methylcobalamin


The information contained on this website is not intended to diagnose, treat, prevent or cure any disease or health condition. It is not intended to substitute for the advice, treatment and medical diagnosis you receive from your GP or other qualified health professional.

As a nutritionist I am not able to make any medical diagnoses, provide second opinions, make claims or provide a substitute for the medical advice you are receiving from your GP or other qualified health professional.  The information on this website is not intended to be used for diagnosing or treating any medical condition or health problem.

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