Vitamin B12 plays a critical role in the metabolism of every cell in the body. It is converted into co-factors that aid the function of specific enzymes involved in DNA synthesis and regulation, lipid and protein metabolism and cell energy production. This translates into important roles in formation of red blood cells, function of the brain and nerves and gastrointestinal health.

Organs or tissues with a high rate of cell turnover like the bone marrow and gastrointestinal tract especially need vitamin B12. Deficiencies can be seen as anemia, digestive disorders like chronic diarrhea, weight loss, poor appetite and neurological problems ranging from minor behavior changes to severe degenerative issues.

Cobalamins are a group of structurally similar compounds that are collectively referred to as vitamin B12. However, biochemical terminology restricts the name, vitamin B12 to a specific form of cobalamin known as cyanocobalamin. It is a water soluble compound that is not stored in the body and can only be synthesized by microorganisms in the colon. Vitamin B12 is found only in animal sources like meat, fish, and eggs unless the food is fortified (supplemented) with vitamin B12.

Even though it was isolated almost 60 years ago, vitamin B12 metabolism is not completely understood. It is a complex, multi-step process. Ironically, even though vitamin B12 is produced by microorganisms in the colon, it is not absorbed into the body in the colon. This means it has to be ingested with food.

There is a complex process for absorption in the body. Initially any free (not bound to protein) vitamin B12 in food is bound by a cobalamin-binding protein found in saliva. As more vitamin B12 is released from food under the influence of digestive processes in the stomach this free vitamin B12 is also bound to the cobalamin-binding protein. In the duodenum (upper small intestine) digestive enzymes release the vitamin B12 from the cobalamin-binding protein. Once released, vitamin B12 is then bound to intrinsic factor from the exocrine pancreas. The exocrine pancreas is the part of the pancreas that produces digestive enzymes and other factors that are secreted into the intestine during the digestive process. Intrinsic factor is a transport protein that allows for absorption of vitamin B12 in the ileum (end of the small intestines). Once absorbed, vitamin B12 is transported to the liver.

With this brief overview it is easy to see potential problems with ensuring that there are adequate levels of this important vitamin in the body. For example, if the pancreas cannot produce enough intrinsic factor, vitamin B12 cannot be properly absorbed. The exocrine pancreas is the major source of intrinsic factor in dogs and the only source in cats. This means that proper function of the pancreas is essential for vitamin B12 absorption. Intrinsic factor is species specific so that the use of bovine pancreatic enzyme extracts are not sufficient to restore vitamin B12 absorption. In addition, if the ileum is diseased or has significant enough reduction in ability to absorb vitamin B12, deficiency can occur. Assuming adequate vitamin B12 in the diet, other potential contributors to poor vitamin B12 absorption include chronic pancreatitis, parasitic infections, inflammatory bowel issues and age.

Measurement of blood levels of vitamin B12 is readily available and can be valuable in a range of health conditions or concerns including chronic digestive problems, weight loss and exocrine pancreas insufficiency (EPI). Supplementation can be done orally with vitamin B12 (cyanocobalamin) or by injection. Oral supplementation may not be as effective for certain problems as the injection is. For example, dogs or cats with disease of the ileum may not be able to absorb adequate amounts of vitamin B12.

If you have questions about vitamin B12 and your pet companion, contact your veterinarian.

Ron Carsten, DVM, PhD, CVA, CCRT was one of the first veterinarians in Colorado to use the integrative approach, has lectured widely to veterinarians and has been a pioneer in the therapeutic use of food concentrates to manage clinical problems. He is also the founder of Colorado Animal Rescue (CARE). In addition to his Doctor of Veterinary Medicine, he holds a PhD in Cell and Molecular Biology and is a Certified Veterinary Acupuncturist and Certified Canine Rehabilitation Therapist. He practices integrative veterinary medicine in Glenwood Springs. Dr. Carsten is the 2022 Colorado Veterinary Medical Association Distinguished Service Award recipient.