Vegan Vitamin B12 – Sources, Absorption, Supplements and Deficiency
June 18, 2021
Vegan Vitamin B12
Vitamin B12, also known as cobalamin is one of the thirteen essential vitamins that the body requires to survive.
It is involved in many crucial processes, including (1) creating DNA, cell division and, maintaining and repairing Myelin Sheath (a protective coating around nerve cells).
This water-soluble vitamin is naturally present in some foods, fortified in others or available as a dietary supplement.
Unfortunately, there are limited vegan vitamin B12 sources as plant based foods do not naturally contain this vitamin. Animal products including meat, chicken, fish, eggs and dairy products are rich in this vitamin.
Consuming enough B12 is crucial for proper blood and brain function and it can be stored in the liver for many years. Deficiency can lead to a range of health consequences including nerve damage and pernicious anaemia.
It is important for those following a vegan or vegetarian diet ensure they are getting enough each day through foods or supplements.
This article explores vitamin b12 on a vegan diet, where you can find it, supplement recommendations and how to avoid deficiency.
How Does Vitamin B12 Function In The Body?
Vitamin B12 is an essential nutrient that almost every cell in the body requires for proper functioning.
Vitamin B12 has two main metabolically active forms. These are methylcobalamin and 5-deoxyadenosylcobalamin.
There are two other forms available – hydroxycobalamin and cyanocobalamin. These forms become biologically active after they are converted to the first two forms.
You may see different forms available in different supplements. Hydroxycobalamin is commonly found in Vitamin B12 injections. Supplements often contain methylcobalamin or cyanocobalamin form.
Vitamin B12 is involved in two main enzyme processes in the body. It acts as a cofactor in these reactions, essentially meaning it becomes a “helper molecule”.
Methylcobalamin acts as a cofactor to the enzyme methionine synthase. Methionine synthase is important for the conversion of homocysteine to the essential amino acid methionine and tetrahydrofolate.
Methionine, is a universal methyl donor. This means it’s essential for a multitude of enzyme processes in the body including DNA, RNA, hormone, proteins and lipids. (2)
Tetrahydrofolate is also produced during this reaction. This is essential as it is an active form of folate, another essential B-vitamin. Deficiency of tetrahydrofolate can also cause megaloblastic anaemia.
5-deoxyadenosylcobalamin acts as a cofactor in the methyl-malonyl CoA mutase transformation of methyl-malonyl CoA into succinyl CoA in the mitochondria (2).
A defect in this reaction is thought to contribute to the neurological effects in vitamin b12 deficiency.
How is it absorbed?
The absorption of vitamin B12 contains a number of steps.
In animal based foods, it is found in the form of methyl-, deooxyadenosyl-, or hydroxy-cobalamin.
When this form of B12 nutrition reaches the stomach, two digestive enzymes – pepsin and hydrochloric acid break down the binding protein, releasing the cobalamin portion of the nutrient known as “free vitamin b12”.
When synthetic (man made) B12 is added to fortified food or supplements, it is already in its free form and therefore does not require this separation step.
Free vitamin b12 then combines with Intrinsic Factor (IF). IF is a type of protein secreted by parietal cells in stomach. This complex is then able to be absorbed in final section of the small intestine known as the illeum.
Absorption can also be influenced by age, reduced gastric acidity and other gut disorders.
This vitamin also has many inactive analogues. These are molecules that look like its active form, but actually are not, and can interfere with it’s function and absorption.
How much vitamin B12 can be absorbed at once?
Vitamin B12 absorption depends on how much is consumed at one time. When added to foods such as soy milk or veggie delight sausages in low amounts (less than 5 mcg per dose) it has a similar absorption rate to animal products. It is absorbed at approximately 56% of a 1mg dose.
Meaning, if you drank a glass of Sanitarium So Good Soy milk which contains 1mcg per cup, you would only be able to absorb approximately 0.5mcg.
This means, that if you take a supplement of 500mcg, you’re only able to absorb 5mcg at one time.
How Much Vitamin B12 Do I Need?
How much you require each day is based on the Recommended Daily Intake (RDI). The RDI is the average daily dietary intake that meets the nutrient needs of 97-98% of the population.
For children under 12 months of age the RDI cannot be determined and therefore Adequate Intake (AI) is used. The AI is based on the average daily nutrient intake deemed to be adequate based on estimates of healthy groups.
Vegan Vitamin B12 Food Sources:
Our bodies can not create B12, meaning that it must be eaten in the diet.
Vitamin B12 is bound to protein. It is found in all animal foods with the exception of honey. This includes meat, poultry, fish, eggs and dairy products (3).
Individuals who follow plant-based diets must rely on fortified foods and supplements to meet their daily requirements.
Vegan vitamin B12 food sources include:
- Certain plant-based milks (i.e. Sanitarium soy milk)
- Nutritional yeast
- Reduced salt Vegemite (note: the original vegemite is not fortified with B12)
- Certain meat substitutes (i.e. Vegie Delights products)
If you are wanting to meet your daily needs through fortified foods it is essential that you read the ingredients list and nutritional panel as not all products listed above will be fortified with this nutrient.
It is also important to note that nutritional yeast, may not be a reliable source. The vitamin levels contained within nutritional yeast can vary between brands, meaning it is not recommended as a sole source B12.
If you want to try and meet your requirements through food alone you will need to consume 2-3 servings of fortified foods, at least 4 hours apart for optimal absorption.
The number of servings required daily will vary depending on which fortified products you consume. Due to this not being feasible for many individuals, it may be beneficial to consider a vegan vitamin b12 supplement.
Poor Sources of Vitamin B12
Some vegan foods claim that they contain B12. This includes tempeh, seaweed, organic foods and spirulina. Unfortunately these contain inactive analogues. This means, when analysing these compounds in the lab they may look like vitamin B12, but they are not biologically active meaning they have no use in the body and can actually interfere with the absorption of active b12.
Some plant foods, such as unwashed potatoes can contain vitamin B12 on their surface. This is due to soil residue or contamination. Unfortunately, this is not a reliable source of this vitamin for vegans. Relying solely on unwashed food products can place you at higher risk for deficiency and food poisoning.
Signs of Vitamin B12 Deficiency
As Vitamin B12 has wide spread use throughout cells in the body, deficiency can cause significant effects.
A 2013 systematic review investigating the prevalence of deficiency among vegetarians and found rates of 62% amongst pregnant women; 32% amongst vegetarians; and 30% to 76% amongst vegans (depending on the definition of deficiency) (6)
Deficiency can be common amongst vegans and those following a mostly plant-based diet.
Studies have also shown deficiency to occur in up to 40% of older adults. This has been linked to issues with absorption, gastrointestinal conditions and use of certain medications.
Sign of vitamin B12 deficiency include (3):
- Megaloblastic anemia, meaning red blood cells are not produced properly and are larger than normal
- Loss of appetite
- Weight loss
- Tingling of the hands and feet
Signs of deficiency in infants include (7):
- Failure to thrive
- Movement disorders
- Developmental delays
- Megaloblastic anemia
Although textbooks state that deficiency can take 2-5 years, our dietitians have seen deficiency occur in as little as 6 months. It is essential to commence supplementation or ensure you are eating adequate amounts as soon as you adopt a completely plant based diet
It is also important for plant-based eaters to regularly check their blood status. Failure to do so can increase the risk of irreversible brain and nerve damage.
What is the best test for Vitamin B12 status?
There are a number of tests available that test vitamin B12 status.
Serum Vitamin B12
Traditionally, vitamin B12 status is assessed by its concentrations in blood (serum) levels.
Unfortunately, there have been recent concerns that these tests are unreliable in the interpretation of the intermediate range of vitamin b12. Some studies have indicated vitamin B12 deficiency may occur at intermediate levels.
According to pathology laboratories in Australia, normal range of serum B12 is defined as 220-900 pg/ml and deficient is <220 pg/ml.
“Active Vitamin B12” or Holo-Transcobalamin
Another test that is commonly used in Australia is called holo-transcobalamin or “active vitamin b12”. This test is often offered as a follow-up test to individuals who have low serum b12 levels.
The Holo-transcobalamin test looks at the total B12 available for tissue uptake. Studies have found that this test has a similar accuracy to the test of serum levels of vitamin b12.
Another concern with this test is that it is only offered for patients with low serum b12 levels. This means that patients with normal b12 levels but are actually deficient are not tested.
In Australia, deficiency is defined as serum holo-transcobalamin levels below 35pmol/L.
Metylmalonic acid (MMA)
Metylmalonic acid (MMA) is a strong indicator of vitamin B12 status.
Their measurement highlights the existence of of deficiency.
It is recommended that an appropriate strategy assess vitamin B12 status is to measure blood (serum) levels of vitamin B12, and follow up low values with MMA.
It is important to note however that this test is not reliable in people with impaired kidney function, common in older people.
Unfortunately MMA is not readily available in Australia.
Increased levels of homocysteine can also be an indicator for deficiency. As vitamin b12 stores fall, serum homocysteine levels increase.
Serum homocysteine levels greater than 9 µmol/L suggest the beginning of depleted vitamin B12 stores and levels greater than 15 µmol/L indicate depleted reserves.
Interpretation should be used with other indicators as levels may also increase with folate deficiency.
What is the best supplement to take?
There are a variety of different B12 supplements available on the market.
Supplements are available as liquids, tablets, lozenges and injections. For the prevention of deficiency, oral supplements are primarily used.
Cyanocobalamin is the most stable and widely studied out of all forms. It has been shown to help prevent and reverse deficiency and therefore is the most commonly form recommended by health professionals. The main exception for this is in smokers, where it is best for hydroxycobalamin to be used.
How frequently should you supplement B12?
There are many different factors that influence how frequently you should supplement vitamin B12. These include age, gender, absorption issues (such as coeliac disease or gastric bypass surgery), increased requirements (pregnancy and lactation), blood test results and ability to remember the supplement.
It would be unethical of us to give you a straight answer as to how much you should have, without knowing your full history and medical background. To work out an appropriate supplement regime for you, book in for a consultation with one of Plant Nutrition and Wellness’s plant-based dietitians.
Should vegans supplement Vitamin B12?
Even though there are some plant-based foods fortified with B12, the selection is quite limited and these foods need to be consumed daily to meet the RDI. There are also cases of vegans experiencing deficiency even when having fortified foods.
For this reason it is often recommended that those that follow a largely plant-based diet to take a supplement.
This is important for all vegans, but especially those with higher requirements such as pregnant and breastfeeding women.
This article was written by Plant Nutrition and Wellness’s founder Kiah Paetz and contributed to by Dietitian Intern Tessa Funk.