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Vitamin B12 deficiency is a common health problem that can have serious consequences – but doctors often overlook it

Diane Cress, Associate Professor of Nutrition and Food Science, Wayne State University, The Conversation on

Published in News & Features

For several months during the summer of 2022, my dog Scout vomited at 3 a.m. nearly every day. If you have a dog, you know the sound. And each time, she gobbled up her mess before I could get to it, making diagnosis of the cause difficult.

The vet and I eventually settled on my hydrangeas as the source of the problem – but keeping Scout away from them didn’t work. She started to seem tired all the time – highly concerning in a typically hyper yellow Lab puppy.

Then one day Scout vomited up a hairball – but not just any hairball. In dogs, hair normally passes easily through the digestive system, but this hairball was wrapped around a brillo pad that was too big to move through. Once this foreign object was removed, the overnight vomiting ended. Scout still needed treatment, though, for a different and surprising reason: The object had inhibited a step in her body’s absorption of vitamin B12. B12 is an essential nutrient involved in proper functioning of blood cells, nerves and many other critical processes in the body.

I’m a registered dietitian, and I teach nutrition and food science to college students, but still I missed the B12 deficiency that was causing my puppy’s fatigue. Doctors can just as easily be blind to it in people – even though B12 deficiency is a common health problem that affects an estimated 6% to 20% of the U.S. population.

B12 is scarce in the diet, and it is found only in foods from animal sources. Fortunately, humans need only 2.4 micrograms of B12 daily, which is equivalent to one ten-millionth of an ounce – a very, very small amount. Without adequate B12 in the body, overall health and quality of life are negatively affected.

One primary symptom of B12 deficiency is fatigue – a level of tiredness or exhaustion so deep that it affects daily life activities.


Other symptoms are neurological and may include tingling in the extremities, confusion, memory loss, depression and difficulty maintaining balance. Some of these can be permanent if the vitamin deficiency is not addressed.

However, since there can be so many causes for these symptoms, health care providers may overlook the possibility of a B12 deficiency and fail to screen for it. Further, having a healthy diet may seem to rule out any vitamin deficiency. Case in point: Because I knew Scout’s diet was sound, I didn’t consider a B12 deficiency as the source of her problems.

Research is clear that people who consume plant-based diets must take B12 supplements in amounts typically provided by standard multivitamins. However, hundreds of millions of Americans who do consume B12 may also be at risk because of conditions that could be hampering their body’s absorption of B12.

B12 absorption is a complex multistep process that begins in the mouth and ends at the far end of the small intestine. When we chew, our food gets mixed with saliva. When the food is swallowed, a substance in saliva called R-protein – a protein that protects B12 from being destroyed by stomach acid – travels to the stomach along with the food.


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