Vegetarian and vegan diets are known for being generally high in fibre, carotenoids, vitamins C, E, folic acid, omega-6 polyunsaturated fatty acids, carbohydrates and magnesium due to their reliance on plant food sources.1 Research into followers of a plant-based diet show reduced cholesterol levels, body mass index, blood pressure and ischaemic heart disease mortality,1 highlighting the appeal of the diets.
However, these diets may be low in protein, omega-3 polyunsaturated fatty acids, vitamins B12, D and A, zinc, iron and calcium, if not managed well, as many of these vitamins and minerals rely on animal sources.1 Of clinical interest is the number of people who follow a vegetarian or vegan diet, who start to recognise their own signs of nutritional deficiency or depletion several years into the diet.
Vitamin B12
Vitamin B12 is involved in cellular metabolism and DNA synthesis in all cells and is the only known vitamin missing from a plant-based diet.2 Deficiency of vitamin B12 can lead to an increased risk of vitamin B12-deficiency anaemia presenting as megaloblastic anaemia and peripheral neuropathy and hyperhomocysteinaemia.2,1
Common signs of vitamin B12 deficiency include:
- Fatigue
- Lethargy
- Breathlessness
- Feeling faint
- Headaches
- Pallor (pale skin)
- Heart palpitations
- Tinnitus
- Reduced appetite and weight loss
- Mouth ulcers
- Pins and needles
- Irritability and depression3
Vitamin B12 stores within the body can decrease over time with reserves in the kidney and liver taking 2-5 years to deplete.2 High dietary folic acid can mask a vitamin B12 deficiency.1
Other causes of vitamin B12 deficiency can include hypochlorhydria, or low gastric acid, and atrophic gastritis resulting in a reduction in vitamin B12 absorption.1
Vegetarian sources of vitamin B12
Vegetarians and vegans are at greater risk of vitamin B12 deficiency, as the major source of vitamin B12 is from the bacteria found in apex predators which are then consumed themselves by humans.1
Small amounts of vitamin B12 can be produced by the intestinal flora of humans.4
Egg yolks do contain small amounts of vitamin B12 (.9-1.4 ug/100 g), however, these may be eliminated from the vegan diet and the bioavailability of the vitamin B12 in a cooked egg is as little as 3.7-9.2%.1
Dairy milk contains very low levels of vitamin B12 (0.3-0.4 ug/100 g), with large losses occurring during the processing of the milk, making it an unreliable source.1
Vegan sources of vitamin B12
Tempeh made from soybeans contains considerably higher amounts of vitamin B12 (0.7-8.0 ug/100 g) due to the bacterial contamination of the soybean during fermentation.1
Lions mane, dried shiitake, black trumpet and golden chanterelle mushrooms have a reasonable amount of vitamin B12, however, huge quantities would need to be consumed in order to meet the recommended dietary requirement for vitamin B12. Lions mane mushrooms contain vitamin B12[c-lactone] that has the ability to bind to intrinsic factor, the vitamin B12 binding protein required for B12 absorption, inhibiting vitamin B12-dependent enzymes.1
Dried green and purple laver algae are the two types of algae that contain 63.6 and 32.3 ug/100 g of vitamin B12. Dried Korean purple laver has been found to contain high amounts of vitamin B12 (133.8 ug/100 g), however, with the drying and seasoning process leading to the colour change from purple to green, the vitamin B12 content is significantly reduced.1 Nutritional studies on vegan children who consumed nori found that nori consumption may prevent vitamin B12 deficiency.1 Eating 4 grams of nori daily can provide a vegan with adequate vitamin B12 and is a good source of iron, and omega-3 polyunsaturated fatty acids.1
Chlorella supplements have been shown to have varying levels of vitamin B12, with vegans advised to check to ensure that their levels were adequate.1
Spirulina, aphanizomenon and nostoc contain reasonable amounts of vitamin B12, however they also contain pseudovitamin B12 which can inhibit the absorption of vitamin B12 and is biologically inactive.1
Bioavailable, vegan sources of vitamin B12 are important for vegans due to the poor representation of this vitamin in their diets.
It is possible to follow a vegan or vegetarian diet and meet all of your nutritional requirements, however, it is also very easy to become nutritionally deficient. Consulting with a nutritionist can ensure that you are on track for good health.
References
- Watanabe, F., Yabuta, Y., Bito, T., & Teng, F. (2014). Vitamin B12-containing plant food sources for vegetarians. Nutrients, 6(5), 1861–1873. https://doi.org/10.3390/nu6051861
- Lederer, A.-K., Hannibal, L., Hettich, M., Behringer, S., Spiekerkoetter, U., Steinborn, C., … Huber, R. (2019). Vitamin B12 Status Upon Short-Term Intervention with a Vegan Diet—A Randomized Controlled Trial in Healthy Participants. Nutrients, 11(11), 2815. doi:10.3390/nu11112815
- nhs.uk. 2022. Vitamin B12 or folate deficiency anaemia - Symptoms. [online] Available at: <https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/symptoms/> [Accessed 18 September 2022].
- Butola, L. K., Kute, P. K., Anjankar, A., Dhok, A., Gusain, N., & Vagga, A. (2020). Vitamin B12 - Do You Know Everything? Journal of Evolution of Medical and Dental Sciences, 9(42), 3139–3146. https://doi.org/10.14260/jemds/2020/688
