Vitamin B-12 in Mushrooms

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Mushrooms can have trace amounts of vitamin B12, but not enough to make them a good source of this vitamin. Most plant-based foods have no vitamin B12, because it is naturally created in the gut of animals. The vitamin B12 found in mushrooms is likely derived from bacteria contamination. Despite a lack of vitamin B12, mushrooms can be a good source of other nutrients.

Mushroom Nutrition

Mushrooms are a nutritious food, offering a variety of vitamins and minerals with few calories. A serving of mushrooms, which equals one-half cup of mushroom slices, has just 8 calories including 1 g protein and less than 0.25 g fat. Half a cup of sliced mushroom provides 3 mg magnesium and 111 mg potassium, making it an excellent source of these minerals.

B Vitamins

The B-complex vitamins are important for maintaining cell reproduction and division and a healthy immune and nervous system. Specifically, vitamin B12 is critical for normal cell division and a deficiency of vitamin B12 causes a condition known as megaloblastic anemia in which red blood cells do not divide normally. While it has only a trace amount of vitamin B12, less than 0.01 micrograms, a serving of mushrooms provides more in the way of other B-complex vitamins including niacin, riboflavin, pantothenic acid, thiamin, cobalmin and vitamin B6. One-half cup serving of mushrooms contains more niacin than any other B-vitamin, providing up to 1.2 mg of this vitamin.

Sources of Vitamin B12

Vitamin B12 is made and stored in the gut of animals. Therefore, plant foods are not a source of vitamin B12 unless they are fortified with it. Fortified breakfast cereals rank as the top third source of vitamin B12. Beef liver, cooked clams and rainbow trout are also excellent sources of this vitamin. Manufacturers use vitamin B12 produced from yeast for fortification.


It is plausible for people to obtain vitamin B12 from mushrooms that are contaminated by manure or bacteria. Any kind of animal waste is bound to carry vitamin B12, which is produced in the gut of all animals. However, the health risks of consuming food contaminated by manure may outweigh the potential beneficial vitamin B12 given manure can harbor serious pathogenic bacteria that can cause illness.