Vitamin B12 on a Vegan Diet: Sources, Doses and Tests

Vegans get vitamin B12 from fortified foods or a supplement, because plants don't make it. The simplest options are a daily supplement of at least 10 mcg, a weekly dose of at least 2,000 mcg, or fortified foods two or three times a day that add up to at least 3 mcg.

The adult RDA is 2.4 mcg a day. Supplement doses look much higher because the body absorbs a smaller share of each dose as the dose gets bigger.

Key takeaways

• Unfortified plant foods aren't a reliable B12 source, including seaweed, spirulina and tempeh.
• Pick one routine: 10 mcg or more daily, 2,000 mcg weekly, or fortified foods 2-3 times a day.
• Read labels: nutritional yeast ranges from 0 to about 18 mcg per serving depending on the brand.
• Cyanocobalamin is the most studied form, and it kept active B12 higher than methylcobalamin in one study of vegans.

How much B12 do vegans need?

The RDA is a daily intake from food, eaten in small amounts across the day. It isn't the dose to take as a single pill.

Three ways to get it

The Vegan Society and the International Vegetarian Union recommend one of these:

Absorption falls as the dose rises. At 1,000 mcg or more, only about 0.5% gets in, so the less often you take B12, the bigger each dose has to be. The same statement advises staying below 5,000 mcg a week, even though toxicity hasn't been shown.

Higher doses are used to correct a deficiency. In a trial of older adults with mild deficiency, it took 647-1,032 mcg a day of oral cyanocobalamin to get most of the improvement in a key blood marker. If you've been vegan for a while without B12, talk to your doctor about testing and the right dose.

Vegan B12 sources: fortified foods

These numbers come from USDA FoodData Central, including the brand label data it collects.

Not every nutritional yeast is fortified. If B12 isn't listed on the label, as with the Frontier entry, don't count it. Fortified breakfast cereals and some meat substitutes also carry B12, but amounts vary by brand, so look for vitamin B12 on the Nutrition Facts panel. Plant milks differ too. Our cow's milk vs soy milk comparison shows a full side-by-side.

Fortified foods can work on their own, but only if you eat them every day. One missed habit and your intake drops to zero, which is why many vegans use a supplement as a backstop.

Vegetarians who eat dairy and eggs get some B12 from them. A 6 oz (170 g) cup of nonfat Greek yogurt has 1.2 mcg and a large egg has 0.6 mcg. That's not much if you only eat them now and then.

Foods that don't count as reliable B12

• Spirulina: in a lab analysis of spirulina tablets, 83% of the B12 was pseudovitamin B12, a form that's inactive in people. It can also make blood tests look better than your real status.
• Nori and other seaweeds: dried nori has some true B12, but studies of vegans have found seaweed inadequate as a main source.
• Barley grass: listed with spirulina and nori as inadequate in direct studies of vegans.
• Tempeh: USDA lists only 0.08 mcg per 100 g.

In the study of vegans described below, people relying on algae, kombucha or other fermented products had the lowest active B12 of any group.

Cyanocobalamin vs methylcobalamin

Cyanocobalamin is the form in most supplements and fortified foods. Methylcobalamin is often marketed as more "natural" or active.

In a 2021 study of 42 vegans in Romania, people taking cyanocobalamin had a median active B12 (holotranscobalamin) of 150, compared with 78.5 for methylcobalamin. More frequent dosing also helped, whatever the form. It's a small study, but there's no good evidence that methylcobalamin works better, and cyanocobalamin is more stable and better researched.

Signs of B12 deficiency and who's at risk

B12 deficiency usually develops slowly, so it can take a long time to show. MedlinePlus lists two groups of symptoms:

• Anemia: tiredness, pale skin, shortness of breath during exercise, a swollen red tongue or bleeding gums, lightheadedness.
• Nerve damage: numbness and tingling in the hands and feet, loss of balance, trouble concentrating, irritability. In severe cases, confusion or vision problems.

Nerve damage may be permanent if treatment doesn't start promptly. If you notice these symptoms, see your doctor.

A review of 18 studies found B12 depletion or deficiency in vegetarians of every age and region, with higher rates in vegans and rates of 62% in pregnant women. Risk is higher if you:

• Are pregnant, breastfeeding or planning a pregnancy.
• Have been vegan since birth, or are raising a vegan child.
• Take metformin or long-term acid-reducing medicine.
• Have celiac disease, Crohn's disease or past stomach surgery.

Testing your B12

A blood test tells you whether your routine is working. Tests your doctor may order include:

• Serum B12: the standard first test. It can be misleading if you take algae products, which contain inactive B12 look-alikes.
• Methylmalonic acid (MMA): the most specific marker. It rises when your cells are short of B12.
• Homocysteine: rises when B12 is low. Vegan Health suggests a level under 10 µmol/L is desirable.
• Holotranscobalamin: the active fraction of B12 in blood.

If you've just gone vegan or skipped B12 for months, ask about a test. Then recheck as your doctor suggests.

A sample B12 day

• Breakfast: oatmeal with 1 cup of fortified soymilk (2.7 mcg).
• Dinner: pasta with 1 tbsp of fortified nutritional yeast (7.5 mcg with the Simple Truth label above).
• Backstop: a 10 mcg or higher daily supplement, or a 2,000 mcg tablet once a week.

That's about 10 mcg from food, more than four times the RDA, as long as both foods are fortified and you eat them every day. For the rest of a vegan plate, see our vegan protein sources, the vegan meal prep plan and plant-based iron sources.

In Nutrify you can turn on vitamin B12 as a custom nutrient, and new barcode scans of fortified foods then log the label's B12 along with the calories. It has a 7-day free trial, then a paid subscription.

Sources

• MedlinePlus, Vitamin B12 (RDAs, food sources), reviewed January 2025.
• MedlinePlus, Anemia due to vitamin B12 deficiency (symptoms, causes, tests), reviewed January 2026.
• Vegan Health, What Every Vegan Should Know about Vitamin B12 (Vegan Society and International Vegetarian Union statement).
• The Vegan Society, Vitamin B12.
• Zugravu CA, et al. Efficacy of supplementation with methylcobalamin and cyancobalamin in maintaining the level of serum holotranscobalamin in a group of plant-based diet (vegan) adults. Exp Ther Med, 2021.
• Eussen SJ, et al. Oral cyanocobalamin supplementation in older people with vitamin B12 deficiency: a dose-finding trial. Arch Intern Med, 2005.
• Pawlak R, et al. How prevalent is vitamin B12 deficiency among vegetarians? Nutr Rev, 2013.
• Watanabe F, et al. Pseudovitamin B12 is the predominant cobamide of an algal health food, spirulina tablets. J Agric Food Chem, 1999.
• Watanabe F, et al. Vitamin B12-containing plant food sources for vegetarians. Nutrients, 2014.
• Niklewicz A, et al. The importance of vitamin B12 for individuals choosing plant-based diets. Eur J Nutr, 2023.
• Melina V, Craig W, Levin S. Position of the Academy of Nutrition and Dietetics: Vegetarian Diets. J Acad Nutr Diet, 2016.
• USDA FoodData Central: soymilk unsweetened fortified 175215, Silk Unsweetened soymilk 175223, nonfat Greek yogurt 330137, hard-boiled egg 173424; Branded Foods: Bob's Red Mill Large Flake Nutritional Yeast 2596118, Simple Truth (Kroger) Nutritional Yeast 2421410, Great Value (Walmart) Nutritional Yeast Flakes 2676401, Frontier Nutritional Yeast Flakes 2273557. Search at fdc.nal.usda.gov.