Vitamin B12 helps keep blood and nerve cells healthy and helps make DNA, and it is found naturally only in animal foods2.
B12 is needed for healthy red blood cell formation1.
B12 supports the development, myelination and function of the central nervous system1.
B12 helps make DNA, the genetic material in all of your cells2.
Like the other B vitamins, B12 is important for protein metabolism3.
| Food and serving | Amount |
|---|---|
| Nutritional yeast, fortified, about ¼ cup | 8.3–24 µg |
| Milk, 2%, 1 cup | 1.3 µg |
| Yogurt, plain, fat free, 6 oz | 1.0 µg |
| Cheddar cheese, 1½ oz | 0.5 µg |
| Food and serving | Amount |
|---|---|
| Clams, cooked, 3 oz | 17 µg |
| Beef liver, pan fried, 3 oz | 70.7 µg |
| Oysters, cooked, 3 oz | 14.9 µg |
| Salmon, Atlantic, cooked, 3 oz | 2.6 µg |
| Tuna, light, canned in water, 3 oz | 2.5 µg |
| Ground beef, 85% lean, 3 oz | 2.4 µg |
Plant foods have no B12 unless it is added, so check labels on cereals and nutritional yeast2. Amounts per serving from1.
Some breakfast cereals and nutritional yeasts have added B12, which the body absorbs well1.
B12 comes in multivitamins, B-complex and B12-only products; shots and a nasal gel are prescription2.
The body holds 1,000 to 2,000 times a typical day's intake, so low levels can take years to show2.
The same reference table draws the reference lines on your charts in Ayuvo. Needs differ in pregnancy and breastfeeding, which are not covered here.
| Age | Women | Men |
|---|---|---|
| 19–30 | 2.4 mcg | 2.4 mcg |
| 31–50 | 2.4 mcg | 2.4 mcg |
| 51–70 | 2.4 mcg | 2.4 mcg |
| 71+ | 2.4 mcg | 2.4 mcg |
RDA (Recommended Dietary Allowance) is the daily amount that meets the needs of nearly all healthy people. Per day, for adults1.
Signs like these have many possible causes. They are a reason to talk to a clinician, not to self-treat.
Low B12 can cause megaloblastic anaemia and nerve problems, and signs may take years to appear1.
No upper limit has been set for vitamin B12 because it has a low potential for toxicity1.
Serum B12 is the usual first check, and methylmalonic acid (MMA) is a more sensitive marker, though MMA also rises with kidney problems and age1.
| Result | What it may mean |
|---|---|
| Serum B12 below 200 pg/mL | Generally low (some labs use 250) |
| Serum B12 200–300 pg/mL | Borderline; MMA can help clarify |
| MMA above 0.271 µmol/L | Suggests low B12 status |
Labs use different units and ranges. Your clinician reads a result alongside your history and other tests.
Supplements most often use cyanocobalamin, and no form has been shown to be absorbed better than another1.
The most common supplement form; the body converts it to active forms1.
One of the two active forms of B12 in the body1.
The other active form, also sold in supplements1.
Used in supplements and, by prescription, as an injection1.
Dissolve under the tongue; studies show no difference from swallowed tablets1.
Supplements can interact with medicines. Talk to a clinician or pharmacist before you start one, especially at high doses.
Natural B12 is found only in animal foods, so people who eat few or no animal foods are at higher risk of low B12. Fortified foods such as some cereals and nutritional yeasts, or supplements, can greatly reduce that risk.
Many older adults make less stomach acid, which is needed to release B12 from food, and conditions like atrophic gastritis also reduce intrinsic factor. B12 in fortified foods and supplements is already free, so it is easier to absorb.
No upper limit has been set because B12 has a low potential for toxicity, and the body absorbs only a small share of large doses. Some medicines can affect B12 levels, so it is worth mentioning supplements to a health professional.
Ayuvo charts vitamin B12 by day, week, month and year, with the reference lines from this page, personalised by age and sex where they differ. Supplements you log in Medications count too. Free, with no account.
Or read the code: Ayuvo is open source
Facts on this page come from these sources, checked on the dates shown. Intake numbers come from Ayuvo's shared reference table, which cites the sources marked for them.
General information, not medical advice. This guide is for healthy adults and does not cover pregnancy, breastfeeding, children or medical conditions. It cannot diagnose or treat anything. Talk to a clinician before starting high-dose supplements, or if you think you may have too little or too much of a nutrient. Spotted an error? Email us.