This article was written by Zachary Wenger, who is a dietetic student and a vegan.
As a follow-up to our previous article, Is Protein Intake an Issue for Vegans, this post will explore vitamin needs for vegans.
There is quite a bit of debate about whether vitamin requirements can be met while following a vegan diet, so let’s take a look at some specific vitamins that are thought to be more difficult to obtain within a vegan diet.
Vitamin B12 is an extremely important nutrient.
It is essential for red blood cell formation, protecting the body’s nerve fibres, DNA synthesis, and neurological functions.
Vitamin B12 is found abundantly in clams, liver, oily fish, meat and dairy.
In the UK, the Recommended Nutrient Intake (RNI) for B12 is set at 1.5 micrograms per day, while in the US, the Recommended Dietary Allowance (RDA) is set at 2.4 micrograms per day (1).
Certain wild mushrooms (black trumpet and golden chanterelle) contain considerable amounts of B12, compared to most plant foods. While this sounds promising, it would take approximately over 100g to achieve the RDA – which is unrealistic for individuals to consume on a daily basis (2). Furthermore, these wild mushrooms aren’t available worldwide and it isn’t clear how well humans absorb this type of B12.
Spirulina is another source of vitamin B12, but researchers have found that much of the B12 is pseudo-B12, which is inactive for humans (3).
Therefore, there aren’t any natural and reliable dietary sources of vitamin B12 on a vegan diet.
As a result, the Academy of Nutrition and Dietetics recommend regularly consuming vitamin B12 fortified foods or a supplement (4). Fortified foods could include plant milks, fruit drinks, cereals, mock meats (i.e. plant-based meat alternatives), nutritional yeast, and more.
In terms of nutritional yeast, small human trials have found this to be effective with increasing B12 levels. It’s important to note though, that the B12 in nutritional yeast is due to fortification and does not actually occur naturally in the yeast. Also, among other things, B12 slowly decomposes when exposed to ultraviolet (UV) light or strong visible light (5). Nutritional yeast is often stored in clear bins or plastic bags, which could destroy a significant amount of the B12. Because of this, the amount of B12 actually absorbed is highly variable.
There is an abundance of research published that links vegan and vegetarian diets to low levels of vitamin B12.
Most notably, research from the EPIC-Oxford study, found that vegans within the trial were 33% lower in vitamin B12 than vegetarians, and 57% lower than omnivores (6).
There are also a small proportion of vegans who believe that they can get by without supplementing vitamin B12 or eating fortified foods. However, there is data demonstrating that in unsupplemented vegans, holotranscobalamin, the active form of vitamin B12 that can enter into cells, decreased in only 4 weeks after the vitamin B12 supplement was stopped (7).
As a vegan, if one chooses not to supplement vitamin B12, this would be considered a true nutrient of concern. However, the vast majority of vegans are aware of vitamin B12’s importance and supplement accordingly.
In short, the most reliable way to meet vitamin B12 needs on a vegan diet, is to supplement. Plain and simple.
Vitamin D is a fat-soluble vitamin that plays an important role in bone health, while also assisting in the absorption of the minerals, calcium and phosphorus.
Vitamin D is unique from other nutrients, as the body can synthesize it through sunlight exposure. Dietary sources of vitamin D include oily fish, egg yolks, and fortified foods.
In the UK, 10 micrograms per day is recommended for those that do not get enough sunlight. This is significant during October to March in countries which are 37 degrees or more above or below the equator, as sunlight does not contain enough ultraviolet radiation for our skin to produce vitamin D due to the angle of the sun during that time of year (8).
Surprisingly, mushrooms that have been exposed to UV light are also a good source of vitamin D (9). However, that source of vitamin D is called vitamin D2. Vitamin D3 on the other hand, is found in animal products and surprisingly in lichen. Both of these vitamins can be supplemented.
Vitamin D3 supplementation does seem to raise vitamin D levels in the body more than vitamin D2 (10-11). This isn’t to say that vitamin D2 is useless. Vitamin D2 still plays a role in improving vitamin D status. It just isn’t as effective as vitamin D3.
Alternatively, vegans are actually able to get their hands on a vegan vitamin D3 supplement, made out of lichen. Lichen is a complex organism that acts as both fungus and algae. When carefully extracted, it contains vitamin D3.
Similar to vitamin B12, many foods and drinks are fortified with vitamin D. This may include breakfast cereals, plant milks, orange juice, and much more. However, it is typically in the form of vitamin D2, not D3.
While vitamin D deficiency may be an issue for vegans, it is also an issue for everyone else.
Over 1 billion people worldwide have subclinical vitamin D deficiency (12). Vegans only make up a small proportion of the global population.
In other words, vegan or not, those that are not getting enough sunlight and have low levels of vitamin D should consider taking a vitamin D supplement.
Vitamin B6 plays a role in over 100 metabolic reactions, including carbohydrate, fatty acid, and amino acid metabolism.
Vitamin B6 also assists in regulating homocysteine levels in the blood and is involved in maintaining brain health through the work of chemical messengers called neurotransmitters.
In the UK, the Recommended Nutrient Intake (RNI) is set at 1.4 milligrams a day for men and 1.2 milligrams a day for women. In the US, the Recommended Dietary Allowance (RDA) is set at 1.3 milligrams a day for men and women.
Without getting too complex, the vitamin B6 found in plants is typically in a specific form called pyridoxine glucoside. This form of vitamin B6, is generally less easy for our body to use than the vitamin B6 found in animal products, known as pyridoxal.
Vitamin B6 absorption from plant-based foods may be reduced up to 75-80% when compared to a form of vitamin B6 found in animal products (13).
Researchers are aware of this, and fortunately for us, research has been conducted on this, specifically in vegans and vegetarians.
Among “strict vegan” German females, despite high dietary vitamin B6 intakes, 18% had insufficient vitamin B6 concentrations (14). Alternatively, the “moderate vegans” within the study, which were basically vegetarians, only 12% had insufficient vitamin B6 concentrations. The further animal foods were restricted, the worse off their vitamin B6 levels were. These findings have been replicated when comparing vegetarians to non-vegetarians in Taiwan, despite their being no significant difference in vitamin B6 intakes among the groups (15). The vegetarians had a significantly lower plasma PLP concentration when compared with nonvegetarians (PLP is just the active form of vitamin B6 in the body).
At this point, it would seem like a closed case. It would seem like vitamin B6, for vegans, is definitely a nutrient of concern. However, there was a small trial conducted in the United States in 1983, investigating vegetarian and non-vegetarians vitamin B6 status and intakes (16). Researchers found no significant differences between the two groups. In addition, there was research conducted in Australia that came to similar conclusions (17). The study aimed to investigate B-vitamin intake and status among omnivores, vegetarians, and vegans. The researchers found that all of the groups had a high prevalence of deficiency. However, while 27.5% of the vegans were vitamin B6 deficient, that was superior to the omnivores and vegetarians, who sat at 30% and 31.4% deficiencies respectively.
Lastly, a study from Switzerland found similar findings (18). When omnivores, vegetarians, and vegans were tested for vitamin B6 status, the researchers, again, found that all of the groups had a high prevalence of deficiency. 24.5% of the vegans were vitamin B6 deficient, which was superior to the omnivores and vegetarians, who sat at 29% and 58.5% deficiencies, respectively.
The variation in outcomes may be explained by the different dietary sources of vitamin B6. As discussed earlier, pyridoxine glucoside is the form of vitamin B6 that is generally less bioavailable. Interestingly, not all plants have the same percentage of pyridoxine glucoside.
For example, if one consumes carrots, the percentage of pyridoxine glucoside has been reported to be anywhere from 51-75% (13). However, if one consumes avocados, the percentage of pyridoxine glucoside has been reported to be roughly 3%. In other words, the bioavailability of vitamin B6, would be much higher for the avocados than the carrots. For those interested, good sources of vitamin B6 that are low in pyridoxine glucoside include avocados, bananas, raw cauliflower, whole-wheat flour, and white rice.
Within the studies that we looked through, we are aware of how much vitamin B6 on average the study participants are consuming. The researchers provide us with that amount. Unfortunately though, we aren’t aware of the different dietary sources of vitamin B6 that the study participants are consuming. This might explain the wide variation out outcomes among the studies.
With the current evidence that we have available, vitamin B6 shouldn’t be considered a nutrient of concern for most vegans.
This may just be a nutrient that one should get blood work on every so often, just to be cautious. There just isn’t sufficient evidence to suggest that this should be something that vegans should actively be worrying about.
However, if a vegan had inadequate levels of vitamin B6, and they were meeting the RDA through diet, there is plausible evidence to explain why that may be the case.
One of the largest fears with adopting a vegan diet is vitamin deficiencies. While it is true that certain vitamins are more scarce within the plant kingdom, there are workarounds including fortified foods, supplements, and specific food choices that make vitamin absorption easier!
Overall, vitamin B12 is the main supplement that all vegans need. Beyond that, it depends on each individual’s diet, sunshine exposure etc. If in doubt, always speak to your GP or to a Registered Dietitian for individual advice.
- “Appendix 3: Table of UK and USA Dietary Reference Values for Vitamins, Minerals and Trace Elements.” Wiley Online Library, John Wiley & Sons, Ltd, 25 Feb. 2008, onlinelibrary.wiley.com/doi/pdf/10.1002/9780470775011.app3.
- Watanabe, Fumio et al. “Characterization of vitamin B₁₂compounds in the wild edible mushrooms black trumpet (Craterellus cornucopioides) and golden chanterelle (Cantharellus cibarius).” Journal of nutritional science and vitaminology vol. 58,6 (2012): 438-41. doi:10.3177/jnsv.58.438
- Watanabe, F et al. “Pseudovitamin B(12) is the predominant cobamide of an algal health food, spirulina tablets.” Journal of agricultural and food chemistry vol. 47,11 (1999): 4736-41. doi:10.1021/jf990541b
- Melina, Vesanto et al. “Position of the Academy of Nutrition and Dietetics: Vegetarian Diets.” Journal of the Academy of Nutrition and Dietetics vol. 116,12 (2016): 1970-1980. doi:10.1016/j.jand.2016.09.025
- Monajjemzadeh, Farnaz et al. “Effects of formulation variables and storage conditions on light protected vitamin B12 mixed parenteral formulations.” Advanced pharmaceutical bulletin vol. 4,4 (2014): 329-38. doi:10.5681/apb.2014.048
- Gilsing, A M J et al. “Serum concentrations of vitamin B12 and folate in British male omnivores, vegetarians and vegans: results from a cross-sectional analysis of the EPIC-Oxford cohort study.” European journal of clinical nutrition vol. 64,9 (2010): 933-9. doi:10.1038/ejcn.2010.142
- Lederer, Ann-Kathrin et al. “Vitamin B12 Status Upon Short-Term Intervention with a Vegan Diet-A Randomized Controlled Trial in Healthy Participants.” Nutrients vol. 11,11 2815. 18 Nov. 2019, doi:10.3390/nu11112815
- NHS Choices, How to get vitamin D from sunlight, www.nhs.uk/live-well/healthy-body/how-to-get-vitamin-d-from-sunlight/
- Keegan, Raphael-John H et al. “Photobiology of vitamin D in mushrooms and its bioavailability in humans.” Dermato-endocrinology vol. 5,1 (2013): 165-76. doi:10.4161/derm.23321
- Tripkovic, Laura et al. “Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis.” The American journal of clinical nutrition vol. 95,6 (2012): 1357-64. doi:10.3945/ajcn.111.031070
- Shieh, Albert et al. “Effects of High-Dose Vitamin D2 Versus D3 on Total and Free 25-Hydroxyvitamin D and Markers of Calcium Balance.” The Journal of clinical endocrinology and metabolism vol. 101,8 (2016): 3070-8. doi:10.1210/jc.2016-1871
- Sizar O, Khare S, Goyal A, et al. Vitamin D Deficiency. [Updated 2020 Jul 4]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan.
- Reynolds, R D. “Bioavailability of vitamin B-6 from plant foods.” The American journal of clinical nutrition vol. 48,3 Suppl (1988): 863-7. doi:10.1093/ajcn/48.3.863
- Waldmann, A et al. “Dietary intake of vitamin B6 and concentration of vitamin B6 in blood samples of German vegans.” Public health nutrition vol. 9,6 (2006): 779-84. doi:10.1079/phn2005895
- Huang, Yi-Chia et al. “The status of plasma homocysteine and related B-vitamins in healthy young vegetarians and nonvegetarians.” European journal of nutrition vol. 42,2 (2003): 84-90. doi:10.1007/s00394-003-0387-5
- Shultz, T D, and J E Leklem. “Vitamin B-6 status and bioavailability in vegetarian women.” The American journal of clinical nutrition vol. 46,4 (1987): 647-51. doi:10.1093/ajcn/46.4.647
- Majchrzak, D et al. “B-vitamin status and concentrations of homocysteine in Austrian omnivores, vegetarians and vegans.” Annals of nutrition & metabolism vol. 50,6 (2006): 485-91. doi:10.1159/000095828
- Schüpbach, R et al. “Micronutrient status and intake in omnivores, vegetarians and vegans in Switzerland.” European journal of nutrition vol. 56,1 (2017): 283-293. doi:10.1007/s00394-015-1079-7