All vegans must ensure sufficient intake of vitamin B12 immediately after adopting a vegan diet.
Why is a vitamin B12 supplement necessary?
Vitamin B12, also called cobalamin, is made by certain bacteria in the digestive track of animals, and passes from there into the animal’s tissues1. In the human body, bacteria in the large intestine produce vitamin B12, but absorption of it happens in the small intestine, which is why vitamin B12 must be acquired from food. Vitamin B12 occurs naturally in significant quantities only in animal products, and therefore vegans must take it as a regular supplement. Some vegan food products have previously been thought to contain vitamin B122. In reality, however, these products mainly contain analogs of vitamin B12 that have no biological activity in the human body, and that may even inhibit the function of active vitamin B123. Consuming seaweed, mushrooms and fermented products does not therefore contribute to intake of vitamin B12. Added vitamin B12 is found in some vegan products, such as fortified plant milks, yogurts, and quarks as well as nutritional yeast flakes. Basing intake on these products alone is not risk-free, which is why it is always recommended that vegans use a vitamin B12 supplement.
How is a vitamin B12 deficiency identified?
In adults with vitamin B12 deficiency, the onset of symptoms takes time, and often clear symptoms are seen only after years of inadequate intake4. Symptoms caused by vitamin B12 deficiency include megaloblastic anemia as well as nervous system related symptoms, such as impairments to sense of touch and memory, weakened muscles, and prickling sensations or numbness in the extremities4, 5. A prolonged vitamin B12 deficiency can cause permanent damage to the nervous system.
Vitamin B12 is classified as a water-soluble vitamin, but despite this classification, our bodies store it in the liver6. The human body also recycles vitamin B12 efficiently – about 75% of vitamin B12 utilized by the body is reused. Due to the efficient storing and recycling of vitamin B12, a deficiency in adults can occur as late as years after adopting a vegan diet. The amount of vitamin B12 stored in the body varies between individuals, which is why some people exhibit symptoms of deficiency faster than others3.
As a vitamin B12 deficiency is easier to prevent than to treat, regular and sufficient supplement use is vitally important. A deficiency is treated by injecting a large amount of vitamin straight into muscle tissue. A vitamin B12 deficiency can raise homocysteine levels in plasma6. Many studies have connected elevated homocysteine levels with a higher risk of cardiovascular disease and stroke7, 8. A vitamin B12 deficiency has also been tied to diminished bone density9. A continuous and heavy intake of folic acid, especially from supplements and fortified foods, may conceal anemia caused by a vitamin B12 deficiency, and the nervous system related symptoms may advance undetected4. A vitamin B12 deficiency is rare in vegans, because those following a vegan diet generally take good care of supplementation.
Where do vegans get vitamin B12?
Vitamin B12 has been added to many food products that are suitable for vegans. Many plant milks, yogurts and quarks, some plant-based cheeses and breakfast cereals, as well as nutritional yeast flakes, contain added vitamin B12. You should always check the amount of vitamin B12 added to the product from the packaging. The vitamin B12 used in food products is always produced by microbes, not isolated from meat or other animal products, and is therefore suitable for vegans3. Fortified food products usually contain only small amounts of vitamin B12, which is why the most reliable and recommended option is to use a separate vitamin B12 supplement in pill form. A supplement is the most reliable option for everyone, but especially those who are pregnant or breastfeeding, as well as children and elderly people. With aging, the body’s ability to absorb vitamin B12 declines.
Vitamin B12 absorption
The absorbability of vitamin B12 is poor and a little complicated. You should therefore not be concerned if a supplement contains as much as 1000 μg of vitamin B12 or more. Even very large amounts of vitamin B12 are not detrimental. The reason for the poor absorption is the limited capacity of the necessary transport protein, intrinsic factor or IF, to bind the vitamin to itself4. The IF-transmitted absorption path is the primary method of absorption for vitamin B12, but only about 2 μg at a time can be absorbed in this way. Of the vitamin that is not bound to IF, approximately 1% is absorbed passively. Passive absorption plays an especially important role when vitamin B12 is taken as a supplement. In practice, this means that the more infrequently you take a vitamin B12 supplement, the larger the required single dose10. The following section includes recommendations for adequate intake of vitamin B12.
Take care to get enough vitamin B12
The important thing in vitamin B12 supplementation is the regular and sufficient use of supplement products. In the 2024 Finnish Nutritional Recommendation, the recommended daily intake of vitamin B12 was increased from 2,0 micrograms to 4,0 micrograms11, 12. From the following table, you can choose a method of supplementation that suits you. Even if you use vitamin B12 as a supplement, you can still eat products that are fortified with it. The doses in the table are for cyanocobalamin, which is the most common form of vitamin B12 in supplements. Cyanocobalamin is the most researched, most reliable and cheapest form of vitamin B12. Adequate intake for other forms, such as methylcobalamin, which is also sold as a supplement, has not been fully ascertained. Therefore, the recommended daily intake for forms other than cyanocobalamin is 1000 µg. Methylcobalamin is a natural and active form of vitamin B12 which the human body can utilize directly without alteration. However, there is no scientific evidence for the notion that either form is unambiguously a better option10, 15.
Table 1. The dose of the vitamin B12 supplement depends on age as well as how often the supplement is taken (sources for the table10, 11, 12, 17).
| Age | Daily recommended intake, Finnish recommendations and EFSA), µg | Dose when supplement is taken daily, µg | Dose when supplement is taken twice a week, µg |
| ≤ 6 m | 0,4 | 0,4 | |
| 7-11 m | 1,5 | 0,5 – 10 | |
| 1 – 3 y | 1,5 | 0,9 – 10 | |
| 4 – 6 y | 1,5 – 1,7 | 1,4 – 10 | 500 – 1000 |
| 7 – 10 y | 2,0 – 2,5 | 7-8 y: 1,5 – 50; 9-10 y: 2 – 50 | 500 – 1000 |
| 11 – 14 y | 3,5 | 11-13 y: 5-50 ; 14 y: 5 – 100 | 500 – 1000 |
| 15 – 17 y | 4 | 5 – 100 | 500 – 1250 |
| Adults | 4 | 5 – 100 | 500 – 1250 |
| Over 65 y | 4 | 50 – 100 | 1000 |
| Pregnant people | 4,5 | 10 – 250 | Not a recommended option |
| Breastfeeding people | 5,0 – 5,5 | 10 – 250 | Not a recommended option |
The previous recommended daily intake for vitamin B12 was 2 µg, meaning that working age adults (excluding those pregnant or breastfeeding) could ensure adequate intake solely by using fortified food products. However, the current recommendation of 4 µg means that for sufficient vitamin B12 intake, you would have to drink approximately one liter of fortified plant milk every day. This amount is not in line with nutritional recommendations or a varied and balanced diet. For many of us, eating habits change from day to day, and therefore using a supplement is the preferrable and most reliable way of meeting vitamin B12 needs. Children following a vegan diet are also recommended to primarily use a vitamin B12 supplement, along with including products fortified with vitamin B12 in their diet.
If you have been vegan for a while but haven’t used a vitamin B12 supplement, or if you have forgotten to use a supplement for an extended period, you should take a daily dose of 2000 µg for two weeks (divided into 1000 µg doses twice per day) to remedy the situation. Alternatively, the body’s vitamin B12 stores can be replenished with a vitamin B12 injection into muscle tissue.
Vitamin B12 supplements suitable for vegans
The vitamin B12 used in supplements is always produced by microbes and therefore suitable for vegans. However, some supplements may contain other animal ingredients. Vitamin B12 supplements sold in Finland that are suitable for vegans include:
- Beko strong (1 mg = 1000 µg)
- Berocca effervescent tablets (10 µg)
- Bethover (1000 µg = 1 mg)
- Betolvex (1000 µg = 1 mg)
- Bioteekki Super B12-vitamiini (1000 µg = 1 mg)
- Bioteekki Vegan B12-vitamiini (500 µg)
- Puhdas + (400 µg / suihkaus)
- Puhdas + Vahva B12-vitamiini (1 mg = 1000 µg)
- VEG1 (25 µg)
- Vitashine VegVit (50 µg)
Determining a vitamin B12 deficiency with a blood test
With regular vitamin B12 supplementation, there is no particular need to measure vitamin B12 levels. Those over the age of 50 should, however, get their vitamin B12 levels measured regularly to catch possible impairments in absorption. The absorption of vitamin B12 deteriorates with age. In the case of impaired absorption, vitamin B12 is given as an injection. Vitamin B12 occurs in the blood in two forms: in active form, bound to transcobalamin, as well as in inactive form, bound to haptocorrin. This is why measuring the overall level of vitamin B12 is not a useful way of finding potential deficiencies14. Vitamin B12 deficiency is primarily determined by measuring the levels of the active vitamin (S -B12-TC2), not the total serum level of vitamin B12 (S -B12-Vit). You should therefore ask your healthcare provider to test for active vitamin B12 levels.
You can find nutritional information for different foods from the Fineli database maintained by the Finnish Institute for Health and Wellbeing.