The recommended value is 3 µg/day for adults. Vitamin B12 cannot be found in plants in amounts worth mentioning, but can be supplemented in the form of fortified products such as soya milk, breakfast cereals and/or dietary supplements. Kelp and spirulina contain B12 analoga which are not active and so they cannot be used to cover the daily need. Bibliographies claiming that those or other vegetables such as fermented soya milk or sauerkraut are sources of B12 are obsolete. With previous measurement methods it was not possible to distinguish between the real vitamin B12 and analoga. Vitamin B12 is saved within the body therefore it takes years for first symptoms - indicating a lack - to show up. Symptoms are anemia or neural degeneration. Small chances in the B12 level can increase the homocysteine which is a risk for cardiovascular disease.
Small amounts can be absorbed much more efficienty than greater ones. Thus, the British Vegan Society recommends either:
- 2 - 3 times a day fortified products and or dietary supplements, in sum 3 µg/day or
- 1 time a day a supplement à 10 µg, or
- 1 time a week a supplement à 2000 µg.
5 µg per day is recommended for adults. Vitamin D does not exist in plant products in amounts to be mentioned. Only in fungi plus the body can synthesize it when exposed to sunlight. Therefore exposing the body to the sunlight preferably on a daily basis is mandatory. In areas north of the 52 latitude (or in the north of Germany during winter) is the necessary wavelength not available. For vitamin D it is also possible to ingest dietary supplements. This applies to especially children, expectant women, elders or people with dark skin color.
Reference level is 1.4 mg/day. Some studies indicate a lower intake of riboflavin for vegans than for omnivors. A clinical lack of riboflavine was not discovered. Riboflavin is widespread in plants but in low quanities. Good sources are yeast flakes and grain foods but also many kinds of vegetables such as green cabbage, peas, broccoli or yellow capsicum.
For men the recommendation is 1.5 mg/day for women 1.2 mg/day. Even in this case it applies that the absorption is a bit less in vegan nutrition. Thus, you should ensure to eat foods with a high bioavailibility of vitamin B6. Thereto belong beans, lentils and bananas.