Can you take too much vitamin B12? How to find your proper dosage, according to dietitians
- You cannot overdose on vitamin B12 because any excess you simply pee out.
- If you get b12 shots, you may experience side effects like dizziness, nausea, and fatigue.
- It is possible to have elevated B12 levels in blood tests, which may indicate cancer or diabetes.
Vitamin B12 plays a key role in many bodily functions, like making red blood cells and supporting the nervous system.
Because of B12's importance, many people choose to supplement it. Here's what you need to know about the side effects of taking vitamin B12 supplements and whether it is possible to take too much.
No, you cannot overdose on B12
It is highly unlikely that someone could take too much B12, says Natalie Allen, RD, a clinical assistant professor of biomedical sciences at Missouri State University.
The Institute of Medicine has not established a tolerable upper intake level of B12 because studies show no adverse health effects when taking excess levels of B12, either through food or supplements.
Medical term: A tolerable upper intake level is the highest level of nutrient intake that does not pose any adverse health effects for the majority of people.
Vitamin B12 is a water-soluble vitamin, meaning it dissolves in water and is quickly absorbed by the body. It is stored in the liver and whatever your body doesn't use is excreted through urine, Allen says. Even in high doses, your body can only absorb a fraction of B12 supplements. For example, a healthy person taking a 500 mcg oral B12 supplement will only absorb about 10 mcg.
Although uncommon, it is possible to have elevated B12 levels in a blood test, says Sheri Vettel, a registered dietitian nutritionist (RDN) with the Institute for Integrative Nutrition.
A serum B12 level between 300 pg/mL and 900 pg/mL is considered normal and levels above 900 pg/mL are considered high.
Elevated levels of B12 could be indicative of certain health concerns, Vettel says, including:
- Cancer
- Diabetes
- Impaired kidney function
- Liver disease
If you have elevated levels of B12, your doctor may run other tests to determine the underlying cause.
Vitamin B12 side effects
Side effects from vitamin B12 supplementation are rare, and only occur with B12 injections, not oral supplementation, Allen says. Vitamin B12 injections are typically used to treat a deficiency in people who are unable to absorb adequate amounts of B12.
The absorption rate from B12 injections is higher than it is from taking supplements, Allen says, which is why it can cause side effects.
Side effects from B12 shots
How much vitamin B12 per day
The recommended amount of vitamin B12 per day is the same for both men and women but varies by age. Here is a breakdown:
| Age | Recommended daily B12 intake |
| 0 to 6 months | 0.4 mcg |
| 7 to 12 months | 0.5 mcg |
| 1 to 3 years | 0.9 mcg |
| 4 to 8 years | 1.2 mcg |
| 9 to 13 years | 1.8 mcg |
| 14+ years | 2.4 mcg |
Important: Pregnant and breastfeeding women need more vitamin B12 to support both themselves and their growing fetus or nursing newborn. Pregnant women need 2.6 mcg of vitamin B12 a day and breastfeeding women need 2.8 mcg.
Most people are able to get enough vitamin B12 from their diets, Allen says, so widespread supplementation isn't necessary. There are some groups who may benefit from or need to supplement due to a B12 deficiency. These include:
- Individuals with pernicious anemia, a condition that causes their bodies to be unable to adequately absorb vitamin B12.
- Older adults over the age of 60 because the stomach lining produces less stomach acid as we age which is needed to absorb B12.
- Individuals with gastrointestinal disorders, like Crohn's or celiac disease. These conditions can inhibit the body's ability to absorb B12.
- Those who have had gastrointestinal surgery, like gastric bypass surgery. These procedures can result in a loss of cells that secrete intrinsic factor - a protein in the stomach needed to absorb B12.
- Vegetarians and vegans who eat minimal animal products, which are rich in B12.
While there's no upper limit to how much vitamin B12 you can take, there are general dosage recommendations.
For example, the Vegetarian Nutrition Dietetic Practice Group recommends that vegans consider supplementing with 250 mcg of B12 per day.
Before starting any kind of supplement, talk with your doctor or a registered dietitian about your diet and health history to determine what supplements you might need and how much you should take.
Insider's takeaway
The Institute of Medicine has not established a tolerable upper intake level of B12 because studies show no adverse health effects when taking excess levels of B12, either through food or supplements.
Side effects from B12 supplementation are rare, but possible when receiving B12 injections. Some people may need B12 supplementation due to certain conditions that inhibit absorption. Talk with your doctor or a registered dietitian about whether or not you should supplement with B12 and how much you should take.