Can you take too much B12? Symptoms, side effects, and safety

High vitamin B12 levels are usually caused by supplements or injections - not food. In most cases, high B12 is not harmful and does not require medical treatment. However, extremely elevated levels or symptoms may signal supplement overuse or an underlying medical condition such as liver disease or kidney disease. The good news is that treating high B12 is simple and effective once the cause is identified. Below are the top ways to treat elevated vitamin B12 and the signs and symptoms to look for.

Vitamin B12 guidelines

For normally healthy children and adults, it’s usually not necessary to take supplemental vitamin B12. Why? Most people get enough vitamin B12 from their diet. In adults, the body needs only 2.4 mcg daily. Pregnant women need 2.6 mcg daily. Breastfeeding women need 2.8 mcg per day. Large doses and injections are only needed in people at risk for vitamin B12 deficiency or who have been diagnosed with vitamin B12 deficiency. 

For vitamin B12, the best way to get enough vitamin B12 is to eat a balanced diet providing all the essential nutrients. The National Institutes of Health Office of Dietary Supplements has a useful list of B12 food sources, including animal products, nutritional yeast, seafood, dairy products, breads, and breakfast cereals. If you’re worried about vitamin B12 intake, then consult this list to change your diet or get advice from a nutritionist or healthcare professional. If you’re considering taking B12 or other vitamin supplements, get medical advice first. 

RELATED: What vitamins should I take?

How to treat high levels of vitamin B12

There is no standard treatment or antidote for too much B12. Instead, treatment focuses on stopping supplementation, reducing B12-rich foods, and addressing underlying conditions. 

Stop or reduce vitamin B12 intake

One way to treat high B12 levels is to stop taking supplements ,  reduce injection doses, or limit foods that are rich in vitamin B12. Examples of foods that are rich in B12 include fish, poultry, eggs, and cereals fortified with vitamin B12. If too much B12 produces symptoms, the only options are symptom relief treatments and supportive care. 

Check for underlying conditions

Certain medical conditions can cause high B12 levels, such as liver disease, kidney disease, and some cancers. Healthcare providers will typically order lab tests if they suspect the cause of your high B12 levels is an underlying disease. If it is, treatment will be geared toward that condition. 

RELATED: How to make sure you absorb your supplements

Signs and symptoms of too much B12?

Most people who take excessive amounts of vitamin B12 do not experience symptoms. Signs of too much B12 are more likely in people taking prescription-level daily doses of 1,000 to 2,000 micrograms or more. Even then, side effects are unlikely. This is because the body does not store large amounts of B12, and excess B12 in the blood is rapidly excreted through the urine. 

1. Skin issues:

   • Acne or rosacea-like rash

   • Skin flushing or redness

2. Gastrointestinal:

   • Nausea or vomiting

   • Diarrhea

3. Neurological:

   • Dizziness

   • Tingling or numbness in hands and feet (peripheral neuropathy)

4. Fatigue or weakness:

   • Feeling unusually tired or weak

5. Anxiety or mood changes:

   • Restlessnes

   • Irritability or mood swings.

Rare but possible symptoms:

1. Elevated blood pressure or heart issues:

   • Increased heart rate or palpitations

2. Allergic reactions:

   • Swelling, itching, or difficulty breathing (requires immediate medical attention)

3. High blood volume:

   • Excessive blood levels of B12 may mimic symptoms of polycythemia (headaches, redness, or blood clots)

4. Worsening of kidney function:

   • In individuals with pre-existing kidney disease, high doses might exacerbate the condition

RELATED: 9 common nutrient deficiencies in the U.S.

Both too much vitamin B12 and too little vitamin B12 may have no symptoms. Some people with low levels of vitamin B12 may have no symptoms, or the symptoms may be subtle. When they do, many of the symptoms are similar to a vitamin B12 excess. The critical difference is this: a vitamin B12 deficiency primarily causes anemia, a shortage of red blood cells. The symptoms of anemia, such as fatigue, feeling lightheaded or dizzy, pale skin, and yellowing of the skin, are critical clues in the diagnosis of B12 deficiency.

RELATED: Vitamin B12 deficiency symptoms: what are the early signs of vitamin B12 deficiency?

Sources

• Vitamin B12 health professional fact sheet, NIH Office of Dietary Supplements

• Vitamin B12 consumer professional fact sheet, NIH Office of Dietary Supplements

• Vitamin B12 (cobalamin), StatPearls

• High B12 level, Cleveland Clinic

• Vitamin B12 injection, Cleveland Clinic

• Association of plasma concentration of vitamin B12 with all-cause mortality in the general population in the Netherlands, Journal of the American Medical Association (JAMA)

• Association of serum vitamin B12 and folate in mortality in incident hemodialysis patients, Nephrology Dialysis Transplantation