B Vitamin Series, Vitamin B12


Vitamin B12, also called cobalamin, is a water-soluble B vitamin. In 1824, J.S Combe first described the fatal form of anaemia, which was the consequential disease associated with degeneration of the stomach. In 1872, Biermer termed this disease as "pernicious anaemia", based on the inevitable outcome of death in individuals that developed this disorder. No cure was found for the disease until 1926 when two physicians, Minot and Murphy, documented an alleviation of the anaemic symptoms by prescribing the inclusion of raw liver into patient’s diets. Their patient recommendations were based off experiments conducted 6 years earlier by George Whipple, who found feeding raw liver to anaemic dogs regenerated their levels of haemoglobin. The same physiological benefit was later seen in humans, and was first known as "extrinsic" factor. For 20 years liver was served as the main source of this unknown curative "extrinsic factor." It wasn’t until 1948 when independent scientists in the United Kingdom and the United States isolated the mysterious factor in crystalline form, giving it the official name of vitamin B12.

What is the prevalence of vitamin B12 deficiency?

Vitamin B12 deficiency is a worldwide issue, as the nutrient is not as prevalent as the other B vitamins within food. In developing countries, the problem is more severe, but developed countries still have high deficiency rates particularly in vegetarian and vegan groups. The Framingham Offspring Study found approximately 39% of adults are at least marginally deficient in plasma B12, defined as the “low normal” range - below 258 picomoles per liter [1]. Supplement users were significantly less likely than non-supplement-users to have concentrations <185 pmol/L (8% compared with 20%, respectively). Among non-supplement-users, there were significant differences between those who consumed fortified cereal >4 times/week (12%) and those who consumed no fortified cereal (23%) [1].

What foods contain vitamin B12?

The best animal-based sources are beef liver, grass-fed beef, raw cheese, cottage cheese, lamb, raw milk, eggs and salmon. Top plant-based sources are fortified plant milks, nutritional yeast, fortified soy products and fortified cereals.

For those that consume limited or no animal-based foods, and also do not consume fortified products, supplementation may be necessary. Meat-eaters that mostly consume white meat may also be at risk of deficiency and need supplementation. B12 supplementation comes in the form on methylcobalamin or cyanocobalamin. Methylcobalamin is the form of B12 that exists in nature, and is pre-methylated, meaning it has superior absorption and tissue retention compared to cyanocobalamin. Cyanocobalamin is lower quality, as the body must remove the cyanide molecule from the vitamin and excrete it, requiring the use of "methyl groups" in molecules that are needed to counteract the effects of homocysteine (high levels cause heart disease) [2].

What are the symptoms of vitamin B12 deficiency?

The most common symptoms of B12 deficiency are weakness, tiredness, light headedness, heart palpitations, shortness of breath, pale skin, constipation, diarrhoea, a loss of appetite, nerve problems (numbness or tingling), muscle weakness, vision loss, and mental problems like depression, memory loss, or behavioural changes.

If you think you have symptoms of vitamin B12 deficiency, you can ask your doctor for a blood test. Supplementation usually cures deficiency, but in severe circumstances B12 injections may be needed.

How much do you need per day?






0-6 months

0.4 mcg

0.4 mcg

7-12 months

0.5 mcg

0.5 mcg

1-3 years

0.9 mcg

0.9 mcg

4-8 years

1.2 mcg

1.2 mcg

9-13 years

1.8 mcg

1.8 mcg

14+ years

2.4 mcg

2.4 mcg

2.6 mcg

2.8 mcg


What are the health benefits of vitamin B12?

Vitamin B12 is required for proper red blood cell formation, neurological function, and DNA synthesis. The nutrient functions as a cofactor for methionine synthase, which initiates the reaction of homocysteine to methionine. Methionine is required for the formation of S-adenosylmethionine, an extensive and prevalent methyl donor for approximately 100 different molecules, including DNA, RNA, hormones, proteins, and lipids.

Positive associations are apparent regarding elevated homocysteine levels and the onset of Alzheimer’s disease and dementia [4]. Inadequate serum vitamin B12 can cause an accumulation of homocysteine in the blood, and might decrease levels of substances needed to metabolize neurotransmitters [5]. B12 intake is therefore inversely associated with cognitive decline [6]. A trial of 195 subjects aged 70 years or older with no or moderate cognitive impairment conveyed 1,000mcg of vitamin B12 supplemented daily for 24 weeks reduced homocysteine concentrations by 36% compared to a placebo [7]. In addition, women in the Women’s Antioxidant and Folic Acid Cardiovascular Study, who were defined as having a low dietary intake of B vitamins, showed a significantly decreased rate of cognitive decline from supplementing 1mg of B12 per day for approximately 1.2 years [8]. More large-scale evidence is needed to confirm this link, although current evidence is promising.

B12’s beneficial effect on lowering homocysteine levels can also reduce the chances of developing cardiovascular disease, as elevated homocysteine promotes lipid peroxidation and impairs endothelial vasomotor function. A study found that 400mcg of vitamin B12 daily, combined with folic acid supplementation, may reduce the risk of developing vascular disease by reducing overall homocysteine levels by 18% [9].

Another highly researched health benefit of B12 is its impact on the nervous system and mood regulation, helping to deal with disorders such as anxiety and depression. The neurological benefits are mainly linked to B12’s role in producing S-adenosyl methionine during one-carbon reactions, known to boost focus and attention [10]. The ability for B12 to lower homocysteine levels may also impact mood states, as a polymorphism (MTHFR C677T) that impairs homocysteine metabolism is shown to be overrepresented among depressive patients [10].

Vitamin B12 is found mainly in beef, cheese, lamb, raw milk, eggs, salmon, fortified plant milks, nutritional yeast, fortified soy products and fortified cereals. It has health benefits such as boosting mood and cognitive skills, forming hormones and DNA molecules, and may prevent cardiovascular diseases, depression, and the onset of Alzheimer’s disease and dementia. A lack of B12 may result in weakness, heart palpitations, shortness of breath, pale skin, nerve problems (numbness or tingling), muscle weakness, and mental problems like depression, memory loss, or behavioural changes. Approximately 39% of adults are at least marginally deficient in plasma B12, with vegetarians and vegans being most at risk. Supplementation of B12 may be necessary for those that are worried about or diagnosed with vitamin B12 deficiency, with methylcobalamin being the superior form of the nutrient.


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Jacques PF, Bostom AG, Wilson P. (2012). Determinants of plasma total homocysteine concentration in the Framingham Offspring cohort. Am. J. Clin. Nutr

Adams M. (2011). Vitamin B-12 warning: Avoid cyanocobalamin, take only methylcobalamin. Available from: http://www.naturalnews.com/032766_cyanocobalamin_vitamin_B-12.html

Institute of Medicine. (1998). Food and Nutrition Board. Dietary Reference Intakes: Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington, DC: National Academy Press

Clarke R. (2008). B-vitamins and prevention of dementia. Proc Nutr Soc

Hutto BR. (1997). Folate and cobalamin in psychiatric illness. Compr Psychiatry

Clarke R, Birks J, Nexo E, Ueland PM, Schneede J, Scott J. (2007). Low vitamin B-12 status and risk of cognitive decline in older adults. Am J Clin Nutr

Eussen SJ, de Groot LC, Joosten LW, Bloo RJ, Clarke R, Ueland PM, et al. (2006). Effect of oral vitamin B-12 with or without folic acid on cognitive function in older people with mild vitamin B-12 deficiency: a randomized, placebo-controlled trial. Am J Clin Nutr

Kang JH, Cook N, Manson J, Buring JE, Albert CM, Grodstein F. (2008). A trial of B vitamins and cognitive function among women at high risk of cardiovascular disease. Am J Clin Nutr

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