The Importance of B12

By Lisa Provost

B12 is water soluble and has the largest and most complex chemical structure of all vitamins. The list of benefits and symptoms of deficiencies are both long. B12 helps to support adrenal function, maintain a healthy nervous system, aid in the production of DNA and RNA, and the production of neurotransmitters. It affects the development and maintenance of red blood cells, nerve cells and normal myelination (the fatty sheaths that cover and protect nerve endings). It’s needed to prevent anemia, required for the proper digestion and absorption of food, and the metabolism of carbohydrates and fats.

A B12 deficiency can cause poor cell formation in the digestive tract and lead to nausea, vomiting, loss of appetite, poor absorption of food (malabsorption syndrome), constipation, gas, weight loss, fatigue, lethargy, abdominal pain, and/or diarrhea. Absorption of B12 requires normal function of the stomach, pancreas and small intestine. These are the very symptoms that cats with IBD and other gastric disorders exhibit. A B12 deficiency also inhibits and decreases the body’s ability to produce blood, increases blood cell destruction, and is very harmful to the nervous system which can cause neurological disorders and severe and sometimes irreversible nerve damage. Because a healthy liver is able to store many years worth of B12, signs of deficiency may not be obvious for a long time.

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. This may be true of pets as well since they are living longer than ever before. No research has ever been done on this.

To be absorbed in the body, B12 needs to combine with a substance called intrinsic factor. IF is produced by your stomach lining where B12 from foods is released from its protein complex by hydrochloric acid and enzymes. The secreted IF will bind to B12 and this combination will travel to the end of the small intestine which then crosses the intestinal wall into the bloodstream. B12 is stored in the liver after being absorbed and anything not absorbed is excreted through the urine.

However, Intrinsic factor concentrates prepared from the stomach of one animal species do not in all cases increase B12 absorption in other animal species or in humans. There are structural differences in the vitamin B12 intrinsic factors among species. Similarly, there are species differences for vitamin B12 transport proteins (Polak et al., 1979).

The cobalt-containing B12 molecule is the largest molecule to be transferred across the intestinal mucosa and transfer occurs only in the ileum. B12 is generally absent from plant and vegetable food sources, unless the food is contaminated by microbes. Ingested B12 is bound to R-proteins and must be liberated by calcium, proteases, and bicarbonate in the duodenum before it can be absorbed. Free B12 then attaches to intrinsic factor (IF) to be transported across ileal cells as a dimer. It is then transported to the liver in the bloodstream bound to transcobalamin-2 (TC-2). The liver is a rich repository for B12 and releases it, as needed into the systemic blood stream. Deficiency of B12 or gastric, intestinal, or pancreatic disorders that affect the absorption of B12 will lead to B12 deficiency. Deficiency of B12 causes pernicious (megaloblastic) anemia by affecting DNA production.

Some risk factors for B12 deficiency are a weakened immune system and impaired white blood cells, gluten allergies and/or sensitivities, helicobacter pylori infection (a bacteria that can be common in IBD) Antacid, H2-blockers (the over use of antacids can cause low B12 and low platelets), anticoagulants and potassium supplements can impair the absorption of B12, broad spectrum use of antibiotics or anti-convulsants and parasites (specifically tapeworm). Large parasites like the beef tapeworm compete for nutrients by robbing the body of micronutrients and vitamins.

Regarding B12 injections for cats: there has been a lot of debate about cyanocobalamin vs methylcobalamin. This is understandable, it is a complicated subject. For humans, there is a lot of marketing promoting methylcobalamin as a superior supplement to cyano, given methyl is a bioactive form, and cyano is not. Yes, cyano is converted by the body into bioactive forms, and this is discussed in more detail, below. Methyl is used primarily in your liver, brain and nervous system and is needed for proper nervous system health. In people with liver disease, although high blood levels of vitamin B12 are common, it is not unusual to actually have a correspondingly low liver tissue concentration of vitamin B12 and its enzymes. With liver conditions, methyl B12 should be used because it helps the liver function much more efficiently. Methyl should be considered in the treatment of all neurological diseases including diabetic neuropathy. Cats with this condition are now being given a dose of at least 3,000 mcgs per day of Methyl B12 with amazing results!

In terms of using methyl instead of cyano for GI diseases, there’s no proof that methyl works better and in fact, methyl breaks down faster and contains a higher amount of preservatives than cyano does. You’re looking for something to have staying power, a longer shelf life in the body. Methyl B12 in the form of injections has no less benzyl alcohol and in fact may contain more than cyanoB12 injections. No version of these injections are without side effects, and caution should always be used. Do your research and make sure your vet knows what you’re giving your cat.

“Cobalamin” is what is termed a cofactor – a cofactor is “a non-protein compound needed for the protein’s biological activity.” There are two cofactor forms of cobalamin: hydroxocobalamin and cyanocobalamin. If a cofactor is organic, it is a coenzyme – the biologically active form. Methylcobalamin and adenosylcobalamin are coenzymes. The cobalamin cofactors go through a chemical process in the body to become coenzymes – but this is what is critical in GI disease – ***each coenzyme has different activity in the body.*** Methylcobalamin is ONE coenzyme, but the non-organic cofactors are metabolized into more than just one coenzyme. Methycobalamin is used specifically in the neural network, and this is why ALL of the “cobalamin” supplementation studies in cats use cyanocobalamin – because it is metabolized into more than just methylcobalamin.

The science on B12 insanely complicated, and they still don’t know much about the process in the body of cats. But what we do have are studies of “B12 supplementation” in cats that typically shows response and results, and the form used was cyanocobalamin. So while I don’t have scientific research that says methylcobalamin is not appropriate for treating B12 deficiency, you can easily find that all neurological-related supplementation is done with methyl, and all GI-related supplementation and research is done with cyano or hydroxo forms.

But importantly, cyano converts into methyl ***AND*** adenosyl coenzymes – and adenosyl is the one that is *required* for energy production by fats and proteins, and it is the adenosylcobalamin that is required for production of hemoglobin.

Methylcobalamin deficiency is associated with specific neurological deficits. So treating with methylcobalamin alone is likely not sufficient, when adenosylcobalamin has the more important role in energy and hemoglobin production. “methylcobalamin addresses ONE very specific aspect of B12 deficiency, and cyanocobalamin converts to the TWO bioactive forms of cobalamin, and if you use methyl, you are using just one that is unresearched and unproven in cats, and gambling that that is good enough.”

Vitamin B12 is found naturally in food sources (principally animal products) in protein-bound forms. The body cannot produce it; it can only store it. The human body has roughly a 3-year supply of B12 and 30% of that found in food is typically destroyed by cooking. Over-processed pet food could be a possible culprit in a lot of these deficiencies, dry food being the worst of the offenders.

Feeding your cat a vegetarian or vegan diet is a death sentence, plain and simple. They are obligate carnivores and the only way to obtain B12 naturally in their diets is through meat. Plants and vegetables do not have much B12 at all, if any. Substituting B12 through vitamins for the purpose of feeding an unnatural diet won’t work. They can only absorb so much of it and they have to convert it. And we are now finding out that most pet food labels are not all that they seem and are not revealing all the ingredients and/or proteins.

B12 injections are illegal to obtain here in the U.S. without a prescription and it might be tempting to go ahead and give your pet a dose of the human version or one that is mixed without a prescription. But I wouldn’t recommend it. The human version may contain more preservatives and if it’s obtained without a script, it’s most likely counterfeit B12 and mixed with who knows what. It may contain toxins of some kind and not even the proper dosing of B12 at all which may lead to you inadvertently putting your pet’s health further at risk.

It’s also been questioned as to whether giving B12 masks the symptoms of diseases and malabsorption syndrome. It used to be thought of that dosing anyone, human or pets, with B12 without testing would not cause harm. But the problem is there are other more serious health conditions your pet can have that can produce high levels of B12 indicating those conditions. Supplementing without a deficiency may in fact mask those conditions such as cancer and hypercobalaminaemia. It’s not as rare as you think to discover high levels of B12 especially in cats with lymphoma present that has not been biopsied.

More studies need to be done and until we have more facts, I recommend your cat be tested for a B12 deficiency first and the dosing left up to your vet, just to be on the safe side. But this should NOT deter you from having your cat tested and treated. A B12 deficiency is serious business and can cause a great deal of serious health concerns.


.50 ml, 1/2 cc


.75 ml, 3/4 cc


1.0 ml, 1 cc

Comments are closed.