There are many myths surrounding the intake of Vitamin B12 and many relate to vegetarian and vegan diets where some of the highest dietary sources of Vitamin B12, including eggs and red meat, are absent or not always consumed regularly. As a Nutritional Therapist, I’ve heard many stories including “You can get enough B12 from the soil on your vegetables if you don’t wash them” or “You don’t need to supplement with Vitamin B12 as you can get enough through the bacteria in your mouth!”
So what is the truth around the intake of this critical B vitamin if your diet does not contain naturally high levels of B12 in the first place?
Vitamin B12 function
Vitamin B12 is a crucial vitamin required for many areas of health including the production of energy, metabolism, red blood cell formation, neurological function, DNA synthesis and maintaining healthy homocysteine levels via the methylation cycle. Despite being water-soluble, this vitamin is stored in the liver so any symptoms from deficiency, such as from chronically low dietary intake, can take up to five years to manifest depending on the original storage level.
Vitamin B12 contains the mineral cobalt and exists in several forms. Compounds with Vitamin B12 activity are called cobalamins. Methylcobalamin and adenosylcobalamin are two natural forms that are bioactive in human metabolism. The other inactive forms are hydroxocobalamin and cyanocobalamin that must be metabolised into the two active forms to be used in human cells and are found in very low levels in algae and some plant foods like chlorella (see below).
Vitamin B12 absorption
B12 digestion and absorption is a complex process and requires the adequate synthesis of gastric (hydrochloric) acid, intrinsic factor (a glycoprotein secreted in the stomach) and proteases (enzymes that break down proteins and peptides).
Simply put, B12 is digested from its protein carrier by pepsin (an enzyme secreted in the stomach), which is activated by hydrochloric acid, and then binds to intrinsic factor for absorption in the small intestine. Vitamin B12 can then be absorbed into the bloodstream through the small intestine.
Vitamin B12 deficiency
Pernicious anaemia (an autoimmune disease) affects the gastric mucosa, leading to the destruction of specialised cells in the stomach (parietal cells) and failure to produce sufficient intrinsic factor, resulting in Vitamin B12 malabsorption and eventually deficiency.
Older adults, who often suffer from decreased hydrochloric acid in the stomach, and individuals with gastrointestinal (GI) disorders may also have compromised absorption of B12, as well as people who rely on Proton Pump Inhibitor (PPI) and antacid medication for long-term acid reflux.
Vitamin B12 deficiency may be characterised by:
• Fatigue, weakness
• Loss of appetite and weight loss
• Soreness of the mouth or tongue
• Neurological conditions, such as numbness and tingling of the hands and feet
• Difficulty with balance
• Poor memory and dementia (e.g. Alzheimer’s disease)
• Low bone mineral density
• Megaloblastic anaemia (i.e. formation of large and structurally abnormal red blood cells)
The neurological symptoms can occur without the presence of
Large intake of folic acid – common in vegan diets due to high levels of plant matter – can mask the damaging effects of B12 deficiency by correcting anaemia without addressing the neurological damage that occurs. High folic acid may even exacerbate Vitamin B12 deficient anaemia and cognitive symptoms so it’s recommended not to exceed 1000mcg daily of folic acid in healthy adults without balancing Vitamin B12 intake and to check Vitamin B12 levels (see below).
This puts into question the need for food fortification. Folic acid added to foods such as bread may well help those in need of increased folate intake but in the absence of correcting Vitamin B12 levels may not be helping all of the population. In fact, epidemiological studies in the United States and Australia, the long-term exposure to food fortification of folate has been demonstrated in elderly folk to worsen neurological symptoms with incipient or definite Vitamin B12 deficiency. The duration of the intake is important. What’s more, those patients with Vitamin B12 deficiency associated with high folate levels have higher levels of homocysteine than deficient subjects with normal folate levels.
In studies focused on homocysteine-lowering cardiovascular disease prevention, the subjects were given small doses of Vitamin B12 in addition to 2.5 mg of folic acid per day for 2 – 5 years without neurological complications, as they were protected from the risk to the nervous system associated with such an excess of folic acid.
There is a very strong case for suggesting that mandatory folic acid fortification policies should always be accompanied by Vitamin B12 fortification or ensuring adequate intake such as from food supplements. There is already evidence that Vitamin B12 deficiency, as well as folic acid, is a risk factor for neural tube defects (NTDs) such as spina bifida, and it has been suggested that the addition of Vitamin B12 to folic acid would further reduce the risk of NTDs resulting from fortification policies.
Sources of Vitamin B12
Vitamin B12 is only synthesised by microorganisms. Thus, it isn’t found in foods of plant origin. Natural animal food sources of Vitamin B12 (which come from the animal’s intestines or from their diet) include fish, meat, poultry, eggs, milk, and milk products, as well as nutritional yeast and even Marmite. Though some bacteria in the small intestines produce B12, it isn’t enough to maintain adequate status in humans.
According to Jack Norris, RD, a vegan expert and co-author of Vegan for Life: Everything You Need to Know to Be Healthy and Fit on a Plant-Based Diet, there are no reliable sources of B12 in plants, contrary to many rumours about sources such as tempeh, seaweeds, and organic produce. Plants have no B12 requirement; therefore, they don’t have any active mechanisms to make or store it. When you find B12 in plants, it’s due to contamination and so isn’t a reliable source.
Many types of seaweed have B12 analogues through their symbiotic relationship with cobalamin-producing bacteria; however, the evidence isn’t clear that this form is active B12 in humans. And fermented foods, such as tempeh, aren’t fermented through B12-producing bacteria so they aren’t a source of B12.
Rumours about bacteria on the surface of organic produce producing B12 haven’t been verified. “Chlorella may improve B12 status, but it’s by such a small amount that I wouldn’t rely on chlorella for B12,” Norris adds. So that’s not to say that these food sources are not worth taking. On the contrary, spirulina, chlorella, seaweed and tempeh contain many other nutritional benefits to enjoy; it’s just they aren’t a reliable source of Vitamin B12.
B12 status in the population
This means that vegetarians – especially vegans – are at risk of Vitamin B12 deficiency, which may take years to manifest. In fact, there’s a high prevalence of low serum Vitamin B12 among vegetarians, in particular vegans, where prevalence ranges at levels between 43% and 88%. In a recent review paper of the National Diet and Nutrition Surveys in the BMJ, the researchers found that 11% of vegan women of childbearing age that were surveyed were clinically deficient in B12 and had significantly higher folate intake through dietary sources. Going back as far as 1955, studies have shown that vegans have experienced Vitamin B12 deficiency. In addition, B12 crosses the placenta during pregnancy and is present in breast milk, thus, if the mother doesn’t receive adequate B12 intake, infants may suffer from B12 deficiency, which can lead to severe, permanent neurological damage.
But, if the National Diet and Nutrition Surveys suggest that 89% of vegans have B12 in the expected blood serum range then what’s the problem for the majority with reportedly okay levels? It all comes down to the detection range of the test, which is believed to be too narrow to pick up more subtle B12 deficiencies, as well as the body’s ability to store B12 for a few years, although the levels will eventually decline if adequate dietary intake isn’t followed. Many people following a vegan or vegetarian diet that have not considered B12 support will have subclinical changes manifesting from dwindling B12 stores that may ultimately lead to long-term health consequences if not addressed.
But it’s not just vegetarians and vegans that are at risk of B12 deficiency. Studies have also found B12 deficiency in different populations including up to 90% of the elderly, 62% of pregnant women, 25%–86% of children, and 21%–41% of adolescents.
So what tests can be done to check B12 levels and should we be supplementing this precious vitamin?
The RDA for B12 in adults is 2.4mcg per day, which assumes a 50% absorption rate from the amount ingested in foods. However, higher levels are often recommended to prevent potential deficiency symptoms in those following low B12 diets, ageing adults and those on medications like PPIs.
In fact, it’s suggested that adults supplement 10 to 50mcg Vitamin B12 additional to the daily diet and vegan adults 18 to 65 years old should consider a daily B12 food supplement boost of up to 100 to 1000mcg daily. The elderly can also supplement up to 1000mcg B12 daily. These higher recommendations than the existing RDA partly stem from the loss of B12 through food processing and pasteurisation, such as with most UK dairy products, and also that only around 50% B12 is absorbed through a healthy gut.
In food supplements, the lower daily doses are typically found in multivitamin and mineral formulations, as well as more concentrated B vitamin complexes and specialist homocysteine support supplements, with the 1000mcg doses of Vitamin B12 formulated as sub-lingual tablets designed for optimal absorption under the tongue, which bypasses the complex stomach digestion and absorption processes allowing for greater absorption. Some medical practitioners prescribe Vitamin B12 injections but of course, these cannot be administered as easily as taking food supplements at home to maintain long-term optimal body and storage levels.
In supplements, B12 is usually present as the inactive cyanocobalamin – a form the body then has to expend energy converting into the bioactive forms methylcobalamin and adenosylcobalamin. Taking food supplements already containing the bioactive forms can, therefore, support bioavailability (i.e. enhanced absorption) and bioactivity of this crucial vitamin.
The status of B12 typically is assessed through serum or plasma B12 levels. Low values may indicate a deficiency but may also indicate low levels of Vitamin B6 and/or folate as these vitamins work synergistically in the cell methylation cycle. Elevated serum homocysteine also indicates an imbalance in B vitamin and methylation cycle activity.
Organic acid urine tests can also detect Vitamin B12 deficiency. Methylmalonic acid (MMA) is a compound produced in very small amounts during amino acid metabolism. Increased production of MMA detected in the urine occurs in Vitamin B12 deficiency. This is because B12 acts as a coenzyme, promoting the conversion of methylmalonyl CoA to succinyl CoA.
Of course, you don’t need to get tested just because you’re vegan! If you have symptoms that indicate low B12 or feel dietary sources are low then checking levels can help indicate the need for higher levels of supplementation.
Clearing up confusions
Vitamin B12 levels are crucial to maintaining long-term health and it’s not always possible to regularly eat or absorbed the high dietary levels of Vitamin B12 required. Age and dietary status are two of the main reasons for Vitamin B12 deficiency, especially if the main sources of meat and dairy are not included for ethical/health/environmental reasons, as with vegan and some vegetarian diets. Daily supplementation of up to 1000mcg B12 with bioactive methylcobalamin and adenosylcobalamin forms through the sub-lingual route helps to bypass the complex stomach and digestive absorption process and improve bioavailability.
If you want to know more information about Vitamin B12 and its place in the methylation cycle then please view this CPD accredited webinar from our education partner
Further reading from Nutrigold:
Tucker et al (2005) Low plasma vitamin B12 is associated with lower BMD: the Framingham Osteoporosis Study. J Bone Miner Res. 2005 Jan;20(1):152-8
Poole JF, Malinow MR, Chambless LE, Spence JD, Pettigrew LC, Howard VJ, Sides EG, Wang CH, Stampfer M. Lowering homocysteine in patients with ischemic stroke to prevent recurrent stroke, myocardial infarction, and death: the Vitamin Intervention for Stroke Prevention (VISP) randomized controlled trial. JAMA. 2004 Feb 4;291(5):565-75.
Lonn E, Yusuf S, Arnold MJ, Sheridan P, Pogue J, Micks M, McQueen MJ, Probstfield J, Fodor G, Held C, Genest J Jr; Heart Outcomes Prevention Evaluation (HOPE) 2 Investigators. Homocysteine lowering with folic acid and B vitamins in vascular disease. N Engl J Med. 2006 Apr 13;354(15):1567-77. Epub 2006 Mar 12.
Hooshmand B et al (2016) Association of Vitamin B12, Folate, and Sulfur Amino Acids With Brain Magnetic Resonance Imaging Measures in Older Adults: A Longitudinal Population-Based Study. JAMA Psychiatry Apr 27.
Morris MS et al (2014) Vitamin B-12 and folate status in relation to decline in scores on the mini-mental state examination in the framingham heart study. J Am Geriatr Soc 60(8):1457-64.
Toole JF et al (2004) Lowering homocysteine in patients with ischemic stroke to prevent recurrent stroke, myocardial infarction, and death: the Vitamin Intervention for Stroke Prevention (VISP) randomized controlled trial. JAMA 4;291(5):565-75.
Selhub J et al (2007) In vitamin B12 deficiency, higher serum folate is associated with increased total homocysteine and methylmalonic acid concentrations. Proc Natl Acad Sci USA 11;104(50):19995-20000
Wang ZP et al (2012) Low maternal vitamin B(12) is a risk factor for neural tube defects: a meta-analysis. J Matern Fetal Neonatal Med 25(4):389-94
Melina V, Craig W, Levin S. Position of the Academy of Nutrition and Dietetics: vegetarian diets. J Acad Nutr Diet. 2016;116(12):1970-1980
Wokes F, Badenoch J, Sinclair HM. Human dietary deficiency of vitamin B12. Am J Clin Nutr. 1955;3(5):375-382
Pawlak Ret al (2013) How prevalent is vitamin B(12) deficiency among vegetarians? Nutr Rev. 2013 Feb;71(2):110-7