Mushrooms do contain vitamin B12, and unlike many other non-animal foods, the B12 in mushrooms appears to be the genuine active form rather than an inactive lookalike. That said, the amounts are small. A typical one-cup serving of fresh mushrooms provides only about 5% of your daily B12 needs, so mushrooms alone won’t keep your levels where they need to be.
The B12 in Mushrooms Is the Real Thing
Many plant-based foods that seem to contain B12 actually contain pseudovitamin B12, a structurally similar compound your body can’t use. Certain seaweeds and fermented foods fall into this category, which is why they’re considered unreliable B12 sources despite what their labels might suggest.
Mushrooms are different. Lab analysis of white button mushrooms using advanced techniques showed that their B12 had identical characteristics to the B12 found in beef, beef liver, salmon, eggs, and milk. It did not match the profile of pseudovitamin B12. This means the B12 in mushrooms is bioavailable, the kind your body can actually absorb and put to work supporting nerve function and red blood cell production.
How Much B12 Different Mushrooms Contain
Not all mushrooms carry the same amount of B12, and the form you buy matters. Dried shiitake mushrooms are among the richest sources, containing roughly 4 to 6 micrograms per 100 grams of dried weight, with some samples testing as high as 12.7 micrograms. Since the adult daily requirement is about 2.4 micrograms, eating around 50 grams of dried shiitake could theoretically meet your daily needs. In practice, that’s a large amount of dried mushrooms to eat every single day.
Fresh mushrooms contain considerably less. One cup of fresh mushrooms delivers only about 5% of your daily B12 requirement. The drying process concentrates nutrients by removing water, which is why dried varieties test so much higher gram for gram.
Why Mushrooms Contain B12 at All
Here’s something most people don’t realize: mushrooms probably don’t produce B12 themselves. The vitamin comes from bacteria living on and within the mushroom tissue, particularly species from the Propionibacterium group. These bacteria are well known for producing B12 and naturally colonize mushrooms during cultivation.
This bacterial origin explains why B12 levels vary so widely between mushroom samples, even within the same species. Growing conditions, the material the mushrooms are cultivated on, and how they’re handled all influence which bacteria are present and how much B12 they produce. Two shiitake mushrooms from different farms could have meaningfully different B12 content, and there’s no way to tell from looking at them.
Can Mushrooms Replace B12 Supplements for Vegans?
The short answer is no. While mushrooms are one of the very few non-animal, non-fortified foods that contain genuine B12, the amounts are too low and too variable to rely on. You’d need to eat a substantial quantity of dried shiitake mushrooms every day, and even then, the actual B12 content of your particular batch is unpredictable.
Registered dietitians are clear on this point: vegans need a regular B12 supplement or consistent intake of fortified foods like fortified plant milks, cereals, and nutritional yeast. These provide standardized, reliable doses. Mushrooms can contribute a small amount of B12 to your overall intake, but they shouldn’t be your safety net.
For vegetarians who eat eggs and dairy, the stakes are lower since those foods provide meaningful B12. Mushrooms can serve as a useful bonus in that context. For anyone eating a fully plant-based diet, though, supplementation remains essential regardless of how many mushrooms you eat.
Getting the Most B12 From Mushrooms
If you want to maximize the B12 you get from mushrooms, dried shiitake is your best option. You can rehydrate them for soups, stir-fries, and broths, or grind dried mushrooms into a powder to add to sauces and seasonings. The B12 appears to be relatively stable in dried form, which is why dried mushrooms consistently test higher than fresh ones even after accounting for water loss.
Fresh white button mushrooms, cremini, and portobello varieties contain smaller but still measurable amounts. Including a variety of mushrooms in your regular cooking adds trace B12 along with other nutrients like selenium, potassium, and certain B vitamins that mushrooms provide in more substantial quantities. Think of the B12 as a small perk of eating mushrooms rather than the reason to eat them.