Can You Take Too Much Vitamin B12? Side Effects, Risks, and What the Latest Research Shows
Vitamin B12 is one of the safest vitamins you can take, and because it’s water-soluble, you might have heard that your body generally excretes any excess through urine. That is partly true.
New research is adding nuance, though. A classic vitamin B12 overdose is uncommon, but too much vitamin B12 can still cause side effects in some people. In fact, some researchers are looking at elevated B12 in the blood to determine what it reveals about an individual’s overall health.
If you’re taking B12 supplements or receiving B12 injections, it’s worth knowing what the latest evidence shows. Here’s what you should know about having too much vitamin B12 in your bloodstream, the possible side effects, and when elevated B12 levels are a cause for concern.
What Is Vitamin B12 and How Does Your Body Handle Excess?
Vitamin B12 promotes several important bodily functions. These include making healthy nerve cells, red blood cells, and DNA.
Specifically, vitamin B12 helps two enzymes in your body function efficiently. These two enzymes are methionine synthase and methylmalonyl-CoA mutase, which are crucial for synthesizing DNA.
Vitamin B12 is water soluble, so when you take more than you need, the body excretes the excess amount through your urine. However, some B12 is stored in the liver for future use.
The ability to flush out the excess B12, though, is why toxicity is rare. But “rare” doesn’t mean impossible. B12 injections and high-dose supplements can result in elevated blood B12 levels in your blood.
Can You Overdose on Vitamin B12?
A classic toxicity overdose isn’t common. Unlike vitamins A, D, E, and K, vitamin B12 doesn’t have an established Tolerable Upper Intake Level (UL) from the National Academies of Sciences, Engineering, and Medicine. What this means is that, currently, there’s no consistent intake level at which the vitamin becomes toxic in healthy individuals.
However, just because there isn’t an established UL doesn’t mean unlimited doses are risk-free. In fact, vitamin B12 side effects and adverse symptoms can occur even without a classic toxicity overdose.
Still, one reason overdoses are rare is that the body has a built-in limit on oral B12 absorption. How much B12 your body absorbs depends on a protein called intrinsic factor. Once this protein becomes saturated, absorption stops.
For example, for normal, healthy adults, the body absorbs roughly 10 mcg of a 500 mcg oral dose. The remainder goes through the digestive system and is eliminated in the urine.
That said, blood tests that show very high B12 levels should be examined by a medical professional, especially if the individual isn’t taking any vitamin B12 supplements. Elevated B12 levels are often point to an underlying condition, not a supplement side effect.
Side Effects of Too Much Vitamin B12
Side effects from too much vitamin B12 typically occur with high-dose supplements or injections. Let’s take a look at some of the too much B12 symptoms:
Headaches
Some people report having headaches after ingesting high doses of vitamin B12. These symptoms are often temporary, however.
Nausea
Nausea can also occur, especially when people start taking B12 supplements or when they increase their dosage.
Diarrhea
Diarrhea has also been reported with high-dose supplements. This is usually a temporary symptom.
Fatigue
Some individuals experience fatigue, though this is rare.
Tingling in the Hands or Feet
High-dose supplements can also cause tingling in the hands or feet. If you experience these sensations and the symptoms persist, talk to your healthcare provider.
Acne and Rosacea Flare-Ups
A common side effect of high-dose vitamin B12 supplements is acne and rosacea flare-ups. Elevated B12 levels can alter the gene expression of the skin bacteria responsible for acne.
Vitamin B12 Injection Side Effects
Vitamin B12 injection side effects differ from those of high-dose oral supplements. Common B12 injection side effects include:
- Injection-Site Reactions: People often report temporary redness, itching, tenderness, bruising, or swelling at the injection site.
- Dizziness: Some patients experience lightheadedness or dizziness right after receiving an injection.
- Skin Rashes: Allergic skin reactions, such as skin rashes and hives, can also occur.
- Acne Flare-Ups: Like with the high-dose oral supplements, B12 injections may trigger acne breakouts.
Rare but Serious Reactions
There are also rare but serious reactions. These include:
- Pulmonary embolism
- Deep vein thrombosis (blood clots)
- Severe allergic reactions
- Anaphylaxis
Anaphylaxis is a life-threatening condition that results in difficulty breathing, swelling of the throat, a drop in blood pressure, and loss of consciousness. If you’re experiencing symptoms of anaphylaxis after a B12 injection, get medical help immediately.
What New Research Says About High B12 Levels
A recent development in B12 research involves elevated vitamin B12 levels. A 2024 meta-analysis by Liu and colleagues, published in Archives of Gerontology and Geriatrics, found that high B12 levels were associated with increased all-cause mortality risk. Specifically, researchers noticed a roughly 4% to 6% increase in mortality risk for every 100 pmol/L increase in B12 concentration.
This new research may sound alarming. However, it’s important to note that the study found an association, not proof that vitamin B12 causes harm. A more likely explanation is that individuals with high B12 levels without supplementation may have liver dysfunction, chronic kidney disease, or blood disorders. These patients are most likely releasing stored B12 into their bloodstream.
Why is this distinction important? If a patient is taking high-dose B12 supplements or is receiving B12 injections, elevated B12 levels are often an unexpected result and may be due to the supplements or injections. However, if lab tests reveal high B12 levels in a patient who isn’t taking supplements or injections, healthcare providers should investigate the cause.
In other words, vitamin B12 in and of itself isn’t dangerous. But elevated B12 levels can be, simply because they serve as a warning sign of an underlying health condition, such as kidney disease or liver dysfunction.
What Is the Right Dosage of Vitamin B12?
The right vitamin B12 dosage differs by age. Here is the recommended daily intake.
- Birth 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
- Ages 14 and older: 2.4 mcg
- Pregnancy: 2.6 mcg
- Breastfeeding: 2.8 mcg
Deficiency Treatment Doses
Treatment for patients suffering from a vitamin B12 deficiency involves larger amounts than the above recommended daily intakes.
Deficiency treatment doses are:
- 1,000 mcg intramuscular (IM) weekly for those newly diagnosed
- 1,000 mcg IM monthly for maintenance
If you’re considering injectable B12 options, read how B12 shots can help you.
Medications That Affect B12 Absorption
Certain medications can affect B12 absorption. These include:
Metformin
Metformin is typically prescribed for type 2 diabetes. The medication can reduce vitamin B12 absorption, particularly when used for a long time.
Proton Pump Inhibitors (PPIs)
Proton pump inhibitors, such as omeprazole and pantoprazole, reduce stomach acid production. Because stomach acid helps release B12 from food, long-term use of PPIs can affect B12 absorption.
Colchicine
Colchicine is typically used to treat gout and some inflammatory conditions. The medication can accelerate the transit time of food in the gut, making it harder for the body to absorb nutrients and vitamins.
Aminosalicylic Acid
Aminosalicylic acid, which is sometimes used for inflammatory bowel diseases, can interfere with B12 absorption by up to 55%.
High-Dose Vitamin C
Taking large amounts of vitamin C can also affect how your body absorbs B12, as the ascorbic acid in vitamin C breaks down and alters the structure of B12. To maximize absorption of both vitamins, take the supplements at different times.
When to See a Doctor
While vitamin B12 supplements are generally safe, make an appointment with a doctor in these instances:
- Before starting a new vitamin B12 supplementation regimen
- If you’re experiencing serious B12 injection side effects
- If your lab tests show high B12 levels even though you’re not taking supplements
- If you’re pregnant or breastfeeding
Frequently Asked Questions
The Bottom Line
Vitamin B12 is safe for most people when they take the daily recommended doses, and true toxicity is rare because the body typically excretes excess amounts through urine. But more isn’t always better, especially via injection. High-dose supplements and injections may cause side effects in some individuals. It’s also important to note that elevated B12 levels usually signal an underlying health condition, such as chronic kidney disease or liver dysfunction. If you plan to start a B12 regimen, talk with your medical provider to determine the right dosage for your age and your needs. To learn more about our vitamin therapy, including vitamin B12 injections and its benefits, visit Drip Hydration’s B12 injections service or read about the connection between B12 shots and weight loss.
Do not refresh this page. If loading takes a few minutes, call 
Processing your booking, please wait...
