Are You Overdoing It On The B12?


By Joy Stephenson-Laws, JD, Founder

Recently, a very good friend of mine who is about 60-years-old told me her blood test came back showing excessive vitamin B12.  

When I inquired what her doctor’s advice was, she said she was told to stop taking her B12 supplements and return in a month to be retested. According to her doctor, my friend’s body was producing “its own B12 and most likely she was over supplementing.”

So I decided to do some research and determine for myself what the consequences of too much vitamin B12 are and whether, in fact, the body produces its own.

What is vitamin B12?

Vitamin B12 is a water-soluble vitamin (as opposed to fat-soluble vitamins like A,D & E). This means it dissolves in water and generally enters the bloodstream soon after consuming it.  

Water-soluble vitamins are generally carried to the body's tissues and then leftover amounts of the nutrient leave the body through urine, reports the National Institutes of Health (NIH).

B12 helps keep the body’s nerve and blood cells healthy and helps make DNA. This is all important for metabolism, cellular and nervous system functions. Vitamin B12 also helps prevent a type of anemia called megaloblastic anemia, which makes people tired and weak.

Some reports say that a B12 deficiency may even lead to depression.

And age may affect how your body absorbs B12.

“Normal function of the digestive system required for food-bound vitamin B12 absorption is commonly impaired in individuals over 60 years of age, placing them at risk for vitamin B12 deficiency,” reports the Linus Pauling Institute.

Taking certain drugs, like proton-pump inhibitors (often used to treat acid reflux), may also affect the way your body absorbs B12.

Can humans produce vitamin B12?

After doing some research, it appears that there is no credible support for the conclusion that our bodies can make its own B12. There are vitamins that the body can produce, like vitamin K and vitamin D. But B12 may not be one of them.

Other animals, fungi and plants are also not capable of synthesizing B12.

“Only bacteria and archaea, also single-celled microorganisms but with an evolutionary history different from that of bacteria, have the enzymes required for its synthesis,” according to one analysis reported in QJM: An International Journal of Medicine.  

It appears we have to get this nutrient through the foods we eat or supplementation. Animal foods such as fish, meat, poultry, eggs and milk contain B12. Generally, plant foods have no vitamin B12 unless they are fortified. As a result, vegans and vegetarians have to especially be mindful about making sure they are not B12 deficient.

Here is where it gets a bit murky and confusing to some. Our bodies can store B12 in the liver for years. So while we cannot make B12, we can store it.

How do our bodies absorb B12 from food?

Now, two things need to happen for our bodies to absorb B12.

First step: hydrochloric acid in the stomach separates vitamin B12 from the protein that it is attached to in food.

Second step: vitamin B12 combines with a protein made by the stomach called intrinsic factor and is absorbed by the body in the small intestine.

Reportedly, “no other micronutrient than vitamin B12 is known to require a specific factor for its absorption."

Some people may have a condition called pernicious anemia, which happens when you cannot make intrinsic factor. This generally makes it difficult to absorb B12 from all foods as well as supplements. As a result, they may experience a decrease in red blood cells.

Can we have too much vitamin B12 in your body?

The answer is yes. Hypercobalaminemia is the medical term for having high serum vitamin B12 levels. Credible reports suggest various reasons why a person may have excessive B12. Some of these include:

  • Excessive intake of B12-rich foods and over supplementation.
  • “By liberation of an internal reservoir.” Essentially, your body releases too much of the B12 it has been storing.
  • An increase in TCB via excess production or lack of clearance.” TCB stands for transcobalamins, which are carrier proteins. There are specific TCBs responsible for delivery of B12 to the body’s cells. If your body has too much of these proteins, you can have too much B12.

Underlying health issues may also be a reason for high B12. For example:

  • Leukemia and other blood cancers and disorders, particularly myeloproliferative disorders.
  • Certain organ cancers
  • Liver disease (such as cirrhosis or hepatitis). A damaged liver can cause you to release too much B12.
  • Kidney disease
  • Hypereosinophilic syndrome, where a person has too many white blood cells

So clearly if you have high B12, you need to get to the bottom of why this is.

Can high doses of B12 be toxic?

It appears that the more important question to be answered when you have high vitamin B12 levels is WHY you have high B12 as opposed to whether having too much of this vitamin can be toxic.

Vitamin B12 does not accumulate to toxic levels. Consuming large quantities does not cause side effects or high levels in your system, whether you get it through food or from taking high-dose supplements,” according to various reports.

The Linus Pauling Institute also supports the claim that high doses of B12 are not toxic.

No toxic or adverse effects have been associated with large intakes of vitamin B12 from food or supplements in healthy people. Doses as high as 2 mg (2,000 μg) daily by mouth or 1 mg monthly by intramuscular (IM) injection have been used to treat pernicious anemia without significant side effects. When high doses of vitamin B12 are given orally, only a small percentage can be absorbed, which may explain the low toxicity. Because of the low toxicity of vitamin B12, no tolerable upper intake level (UL) has been set by the US Food and Nutrition Board.”

It is, however, important to note that too much B12 may cause issues in certain cases.

In some people, high levels of B12 may cause gastrointestinal problems such as bloating and diarrhea.

And if you have high blood pressure or poor cardiovascular health, having too much B12 may further complicate these issues.

Pregnant and breastfeeding women may also need to be especially mindful of B12 levels.

How can we be proactive?

Ask your doctor for a vitamin B12 level blood test. If your test shows that you have high B12, it might not be a bad idea to undergo a full examination and panel of tests to see why this is.

It may be as simple as you are consuming too much of it in your diet or are over supplementing, but if this is not the case you want to see if it is a result of a liver, kidney or blood disease.

And although high doses of B12 may not be toxic, I believe being nutritionally balanced is key in maintaining your overall health. You don’t want to have nutrient deficiencies, but you also do not want to have too much of a certain vitamin or mineral.

So taking a nutrient test will determine where you stand as far as your nutrients like vitamins, minerals and protein are concerned.

Do not wait for symptoms of illness to appear before you get a nutrient test. You can feel perfectly fine but still have deficiencies or imbalances that may be affecting your health and mood.

Like my friend, if your results show that you are imbalanced, work with a competent healthcare professional to tweak your diet and/or take good quality supplements.

Finally, after review of the relevant research in this case, it is my opinion that my friend’s doctor may be incorrect by concluding that my friend’s body was making too much vitamin B12. The body does not make this vitamin. However, it is possible that my friend may be over supplementing or eating too many vitamin B12 foods. So returning to the doctor after 30 days to determine what her levels are after halting any B12 supplements she might be taking may actually be good advice. If her B12 is still high at that time, then it is important to assess what is causing the increased levels.

Enjoy your healthy life!

The pH professional health care team includes recognized experts from a variety of health care and related disciplines, including physicians, attorneys, nutritionists, nurses and certified fitness instructors. This team also includes the members of the pH Medical Advisory Board, which constantly monitors all pH programs, products and services. To learn more about the pH Medical Advisory Board, click here.   


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