Vitamin B12, which is also known as cobalamin, is an important vitamin for all sorts of bodily processes. It is used to create amino acids and fatty acids, and is also used by the body to make new DNA whilst cells are being repaired and new cells being born. B12 also helps to make myelin, an important part of the nervous system, and helps in the production of new red blood cells. It’s used in every single cell in the body at some point, so going without Vitamin B12 quickly causes lots of problems.
Cobalamin cannot be made by animals, it’s made by bacteria that live in the guts of ruminants like sheep and cows. These animals absorb some of the vitamin and this is how it enters the food chain. Your dog or cat gets B12 in their diet from eating beef or lamb. When it reaches the gut it goes through a process of both active and passive absorption. That is, special transporters use precious energy to move around 99% of the B12 through the gut wall, whilst the other 1% is absorbed by diffusion. Excess B12 is stored in the liver, which can store enough vitamin B12 to last about 3 weeks. If these stores are overwhelmed, the water-soluble vitamin is excreted from the body in urine.
There are three main causes of low B12. One is not getting enough in the diet, although this is rare as most commercial diets have plenty of B12 in. However, vegan diets contain little to no B12 and this can cause a problem. If you are considering feeding or trying to feed your dog or cat a vegan diet it’s best to talk to your vet about ensuring they still get all of the nutrients they need to survive.
Another cause of low B12 is a genetic inability to absorb it. This is most common in Border Collies, Giant Schnauzers and Beagles. These puppies will initially grow normally, but will then become lethargic, inappetant and have neurological symptoms such as wobbliness and seizures.
Adults can also become unable to absorb B12. This usually occurs due to long-term diarrhoea. Anything that causes diarrhoea can cause an inability to absorb B12, including intestinal cancer, pancreas problems and irritable bowel disorders. This means that dogs predisposed to this sort of problem- such as German Shepherds- are more prone to B12 deficiency. A misbalance of bacteria in the intestine is also a common cause of a lack of absorption of vitamin B12. Short-term diarrhoea can upset absorption, but thanks to the three-week store in the liver it’s not normally a major problem.
Because Vitamin B12 is essential in so many areas, the symptoms of low B12 can be varied, and are often not very specific.
In older dogs, the most common symptom is in fact the cause- diarrhoea lasting for more than a week or so. Any animal with cobalamin deficiency may also become weak, unwilling to eat and wobbly. You may also notice extreme weight loss, loss of muscle mass, and loss of mental ability. If your dog has any of these signs and is an at-risk breed, has had vomiting or loose stools, or is not on a commercially-prepared meat-based diet you should take them to the vet as soon as possible, as vitamin B12 deficiency can be fatal.
If your vet suspects low B12 (or ‘hypocobalaminaemia’) they can do a blood test. This test needs to go off to the lab and it can take a few days to get a result. For this reason, we often supplement cobalamin even in cases where we aren’t sure it’s a problem. There’s no harm in doing this as any excess cobalamin that can’t be stored will be passed harmlessly in the urine.
There are two ways to supplement your dog’s B12 levels if required. One is to inject B12 under the skin so that it is quickly absorbed directly into the bloodstream. This can sting, but ensures that high levels of B12 are available for use by the cells in the body. It completely bypasses the digestive tract, which can be important if your dog has a damaged gut or if they have a genetic problem with absorbing the cobalamin. We normally recommend an injection a week for four weeks, although this varies entirely on the needs of the dog or cat.
There are also oral supplements. Although it seems illogical to give oral supplements to a dog struggling to absorb cobalamain due to a damaged gut, it does work. This is because of the 1% that is absorbed via diffusion. We aim to load the gut with cobalamin so that the 1% is a large enough amount that the dog has all the cobalamin they need. Oral supplementation is especially useful for cases that need long-term supplementation or those that really struggle with having the injection. Cats in particular find that the injection stings and oral supplementation is likely to be extremely beneficial to them.