Vitamin B12 Deficiency is Common, But Are we Also Facing an Epidemic of Too Much B12?

By Dr. J.E. Williams | | Reading Time: 6 minutes

Vitamin B12 blood test

The National Institutes of Health (NIH) warns against Vitamine B12 overdose. Vitamin B12 is a water-soluble nutrient obtained from your diet or supplements. Any excess gets excreted in the urine. The problem started in the last decade with the availability of highly efficient oral and injectable forms of B12. It’s mainly these forms that lead to high B12 blood levels. Though not yet proven, limited evidence suggests an increased cancer risk in those with higher-than-normal B12 levels. Can you get B12 overload, and is it dangerous? 

Vitamin B12 is a water-soluble nutrient obtained from your diet or supplements. Any excess gets excreted in the urine. The problem of excess B12 started in the last decade with the availability of highly efficient oral and injectable forms of B12. It’s mainly these forms that lead to high B12 blood levels. 

An Epidemic of Too Much Vitamin B12 

I started clinical practice over forty years ago, a time when vitamin B12 was considered a “cure-all.” Many people weren’t getting enough vitamin B12 from their diet unless they ate organ meats like liver and lots of fish and shellfish. The result was an epidemic of vitamin B12 deficiency, especially in the northern climates of Europe, Russia, and North America. Women were more prone to insufficient vitamin B12 because of blood loss from their monthly menstrual cycle. And vegetarians, especially vegans, are often deficient or have inadequate levels of vitamin B12 on a blood test. Not enough B12 is a cause of fatigue, poor cognitive function, and is linked to increased cancer risk. 

The Revici Method advocated altering the body’s biochemical landscape to treat cancer patients, including B12 injections. Conventional medical doctors (MDs) routinely gave monthly B12 shots, especially to women patients, for vague symptoms from anxiety to fatigue. None of it did much good unless the patient didn’t have enough B12 based on a blood test. In that era, few doctors checked B12 levels. 

In response to the failures of B12 therapy by MDs, naturopathic doctors (NDs) claimed that typical B12 shots used cyanocobalamin, an inactive form of B12 that didn’t work well. Instead, they recommended methylcobalamin, a form of B12 where a methyl group replaces the cyano group. 

More Efficient Forms of Vitamin B12 

Methylcobalamin is considered the active form of B12, but it’s technically not the same as vitamin B12. Oral methylcobalamin gets converted into adenosylcobalamin, and regenerates some of the methylcobalamin. 

Elite nutritional supplement companies offered a combination of adenosylcobalamin and methylcobalamin, claiming better body compatibility and superior effectiveness. But a better choice is combining adenosylcobalamin and hydroxocobalamin, a precursor of vitamin B12 that benefits the myelin nerve sheath and supports mitochondrial health. 

These new oral B12 forms provide better absorption. They quickly increase vitamin B12 levels on a blood test when taken daily. But the result has become an epidemic of too much B12. It’s not uncommon to see B12 levels over 2,000. The normal range is 200-1100 pg/mL. In some cases, levels exceed 3,000 pg/mL. 

Can You Take Too Much Vitamin B12? 

The body tolerates high doses of B12 but taking too much over time may cause many unexplained symptoms. Judging your B12 status by symptoms can get confusing because some of the symptoms of high vitamin B12 are commonly associated with B12 deficiency. People with chronic kidney or liver disease can accumulate B12 due to lower detoxification function when these organs are impaired. My concern is that such high levels may have subtle toxic effects. 

Vitamin B12 overdose Symptoms:

  • Headache
  • Nausea and vomiting
  • Bloating
  • Diarrhea 
  • Fatigue and weakness
  • Tingling in hands and feet
  • Dizziness
  • Itchy, burning skin
  • Acne
  • High blood pressure

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There are few studies for vitamin B12 overdose, but some medical experts suggest potential harm from B12 overload: 

It’s unlikely that high vitamin B12 can occur without the overuse of high-efficiency oral or injectable B12. If your B12 is too high, check with your doctor to rule out liver disease, diabetes, leukemia, and other cancers. And reduce your B12 intake to lower the risk for toxicity.

What’s a Safe Dosage for Vitamin B12?

According to the National Academies of Sciences, Engineering, and Medicine (NAP), a safe highest level is called the “tolerable upper intake level.” Assessment of what amount is too much is based on animal and human studies, published evidence of adverse events, and professional agreement based on a committee of experts. 

Vitamin B12 capsules
Pure - Vitamin B12 liquid

Read your vitamin B12 supplement label. Suppose you take 1000 mcg or less of cyanocobalamin or methylcobalamin in tablet or capsule form. In that case, there’s little concern that you’re overdosing. Increase your dose to 2000 mcg or change the form of B12. 

If you take 2000 mcg or more of adenosylcobalamin with hydroxocobalamin, you may get too much vitamin B12. Check your level by a blood test.  If it’s high, lower the dose to 1000 mcg or take 2000 mcg every other day. Retest in 60-90 days. 

Suppose you get vitamin B12 injections weekly or monthly and take oral adenosylcobalamin or hydroxocobalamin. In that case, you very likely are getting too much. To prevent toxicity, check your B12 level with a blood test every 4-6 months.

Too little B12 causes low energy and poor health. Pure Encapsulations (capsules or liquid) and Seeking Health (lozenges) are trusted sources that I prescribe for my patients. Take one daily (adenosylcobalamin and hydroxycobalamin 50/50%, 2000 mcg per capsule). But don’t overdose on vitamin B12. Too much may have adverse health consequences.

The B12 Blood Test 

A blood test is the only way to know if you’re getting too much or not enough vitamin B12. Quest Diagnostics and LabCorp, the two largest clinical laboratories, offer direct lab ordering to health consumers. Or request your doctor to order tests for you.  

General Comments & Additional Information
Clinical Info: NORMAL REPORT

Ordered items
Vitamin B12

TestResultFlagUnitsReference IntervalLab
Vitamin B12450pg/mL232 – 124501

What’s A Safe Level? 

We used to think that B12 was completely safe. If you took too much, the kidneys removed it from the bloodstream in the urine. In my early days of practice, doctors called this “expensive urine.” 

Based on a blood test, the lower limit is 232 pg/mL, with an upper limit of 1245 pg/mL. But falling within the range doesn’t mean an individual gets enough B12 for optimal tissue function. 

The preferred way to test B12 status is also to check your methymalonic acid (MMA) level. If your MMA is high, you may have vitamin B12 deficiency. Like too much B12, low MMA so far has no known health risks. 

General Comments & Additional Information
Clinical info: NORMAL REPORT

Ordered Items
Methylmalonic Acid, Serum

TestResultFlagUnitsReference IntervalLab
Methylmalonic Acid, SerumA225nmol/L0 – 37801

Another way to evaluate the physiological value of B12 is by testing total serum homocysteine. If your homocysteine level is high, you don’t have enough B12, folate, and vitamin B6. 

Ordered items

TestResultFlagUnitsReference IntervalLab
Homocyst(e)ine12.3umol/L0.0 – 14.501

How To Check Your Vitamin B12 Level

You no longer need to see a doctor for a B12 test. Use QuestDirect or LabCorp OnDemand, or a patient-direct ordering service like Ulta Lab Tests. Make an appointment through the lab’s online webpage to have your blood drawn. Or schedule a mobile phlebotomy service to come to your home. During the pandemic, more of my patients want to get tested but were reluctant to come to the office or go to a laboratory draw center. 

Comprehensive B12 Status Panel

Vitamin B12
Methylmalonic Acid

Vitamin B12 FAQs

Is too much B12 toxic?

In the short term, no. But it’s possible low-grade toxicity could develop over time.

Can you get too much vitamin B12?

Yes, your B12 levels can go too high when using high-efficiency forms of B12.

Is B12 testing necessary?

Absolutely. You need to know that what you’re taking orally or by injection is working, and if you’re getting too much.


More efficient oral and injectable forms may cause B12 overload. It’s too early to know if too much B12, based on high levels from a blood test, is a health concern. Until we know more, I advise taking highly efficient forms of B12 to ensure you get enough but test your B12 level to prevent B12 overload. 

There are still lots of unknowns about B12. Too much B12 by blood testing indicates your form is working. However, no matter the source, you’re accumulating more than your body can excrete in urine and stool. 

There is no consensus on the tolerable upper intake level of vitamin B12 or if too much is toxic. Though there appear to be no risk and few symptoms associated with too much B12, it’s wise to keep your level within the upper limit of the standard test range.