Vitamin B12 is made by certain bacteria not by animals or humans. The most common source for humans is from eating animal products (meat, dairy and eggs). The animals get it from the bacteria in their GI tract, the bacteria on the food they eat, and it is sometimes given to them in feed or by injection. Humans have bacteria in their GI tract, with the vast majority in the colon and they produce very little vitamin B12. Unfortunately, humans are unable to absorb the vitamin B12 produced in the colon because vitamin B12 is only absorbed in the small intestine, which is upstream of the colon. It is difficult to get adequate B12 from bacteria on plant foods alone because we clean, wash and cook our food.
There are many factors that can predispose someone to low B12 levels including:
- History of stomach surgery or inflammatory bowel disease
- Prolonged use of certain medications including Metformin and certain heartburn medicines
- Age >50
- Reduced intake of foods from animals
B12 can be found in small amounts in fortified foods like soy milk and nutritional yeast, but the most reliable way to ensure you obtain adequate B12 is to take a supplement. While our bodies only need 2.4 micrograms (µg) of vitamin B12 per day, higher amounts need to be taken as a supplement to allow enough absorption. Take cyanocobalamin, the most common form, either alone or in a multivitamin.
1. If you take metformin or are 65 years or older:
Take 500 micrograms (µg) vitamin B12 per day
(acceptable range is 100-1000 ug per day).
2. If you eat a mostly or fully plant-based diet and are under age 65:
Take 1000 µgs 2 - 3 times per week
(alternatively, if you prefer a daily supplement, take 25-100 µg per day).
Follow-up with your healthcare provider to discuss testing your levels and your individual need for supplementation, especially if you take Metformin, are over 65 and/or eating mostly plant-based.