For several months in the summer of 2022, my dog Scout threw up at 3am almost every day. If you have a dog, you know the sound. And every time she would swallow her mess before I could get to her, making it difficult to diagnose the cause.
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 look tired all the time – very alarming in a typical hyper yellow lab puppy.
Then one day, Scout threw up a hairball—but not just any kind. Hair usually passes through the digestive system easily in dogs, but this hairball was wrapped around a pad that was too big to pass through. Once this foreign body was removed, the nocturnal vomiting ended. However, Scout still needed treatment for a different and surprising reason: the object had blocked a step in her body’s absorption of vitamin B12. B12 is an essential nutrient involved in the proper functioning of blood cells, nerves, and many other critical processes in the body.
I am a registered dietitian and teach nutrition and food science to students, but I still missed the B12 deficiency that was causing my puppy’s fatigue. Doctors can just as easily be blind to it in humans – even though B12 deficiency is a common health problem affecting about 6% to 20% of the US population.
B12 is scarce in the diet and is only found in foods of animal origin. Fortunately, humans only need 2.4 micrograms of B12 daily, which is equivalent to one ten-millionth of an ounce—a very, very small amount. Without enough B12 in the body, overall health and quality of life are negatively affected.
Signs and symptoms
One major symptom of B12 deficiency is fatigue—a level of tiredness or exhaustion that is so profound that it affects daily activities.
Other symptoms are neurological and may include numbness in the extremities, confusion, memory loss, depression, and difficulty maintaining balance. Some of them can be permanent if the vitamin deficiency is not addressed.
However, because there can be so many causes for these symptoms, healthcare providers may overlook the possibility of a B12 deficiency and not check for it. Additionally, having a healthy diet may seem to rule out any vitamin deficiency. Case in point: because I knew Scout’s diet was healthy, I didn’t think B12 deficiency was the source of her problems.
How B12 is absorbed
Research shows that people who eat a plant-based diet should take B12 supplements in amounts normally provided by standard multivitamins. However, hundreds of millions of Americans who consume B12 may also be at risk due to conditions that may prevent their body from absorbing B12.
B12 absorption is a complex multistep process that begins in the mouth and ends in the distal end of the small intestine. When we chew, our food is mixed with saliva. When 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 with the food.
Specific cells in the stomach lining, called parietal cells, secrete two substances that are important for the absorption of B12. One is stomach acid – it separates food and B12, allowing the vitamin to bind to the R-protein in saliva. The other substance, called intrinsic factor, mixes with the contents of the stomach and moves with it into the first part of the small intestine, the duodenum. Once in the duodenum, the pancreatic juices release B12 from the R-protein and pass it on to intrinsic factor. This pairing allows B12 to be absorbed into the cells, where it can then help maintain nerve cells and form healthy red blood cells.
B12 deficiency usually involves a breakdown at one or more of these points on the absorption pathway.
Risk factors for B12 deficiency
Without saliva, B12 will not bind to the R-protein in saliva and the body’s ability to absorb it is inhibited. And there are hundreds of different medications that can cause dry mouth, resulting in too little saliva production. These include opioids, inhalers, decongestants, antidepressants, blood pressure medications, and benzodiazepines, such as Xanax, used to treat anxiety.
The last three categories alone account for easily 100 million prescriptions in the US each year.
Another potential factor for B12 deficiency is low stomach acid levels. Hundreds of millions of Americans take antiulcer medications that reduce stomach acids that cause ulcers. Researchers have strongly linked the use of these drugs to B12 deficiency – although this possibility may not outweigh the need for the drug.
Stomach acid production can also decrease with age. More than 60 million people in the US are over the age of 60, and about 54 million are over the age of 65. This population faces a higher risk of B12 deficiency – which can be further increased by the use of antacids.
The production of gastric acid and intrinsic factor by specialized parietal cells in the stomach is critical to achieving B12 absorption. But damage to the stomach lining can prevent the production of both.
In humans, damaged stomach lining results from gastric surgery, chronic inflammation, or pernicious anemia, a medical condition characterized by fatigue and a long list of other symptoms.
Another common culprit for B12 deficiency is inadequate pancreatic function. About one-third of patients with poor pancreatic function develop B12 deficiency.
Finally, metformin, a drug used by about 92 million Americans to treat type 2 diabetes, has been associated with B12 deficiency for decades.
Treatment of B12 deficiency
While some health care providers routinely measure levels of B12 and other vitamins, a typical screening exam includes only a complete blood count and a metabolic panel, neither of which measure B12 status. If you are experiencing potential B12 deficiency symptoms and also have one of the risk factors above, you should see a doctor to be tested. Appropriate laboratory testing and discussion with a physician is necessary to detect or rule out whether inadequate B12 levels may be at play.
In the case of my dog Scout, her symptoms prompted the vet to run two blood tests: a complete blood count and a B12 test. These are also good starting points for people. Scout’s symptoms disappeared after several months of oral B12 supplements, which also contained the active form of the B vitamin folate.
In humans, the type of treatment and length of recovery depends on the cause and severity of the B12 deficiency. Full recovery can take up to a year, but is very possible with proper treatment.
Treatment for B12 deficiency may be oral, sublingual or nasal, or may require different types of injections. A B12 supplement or balanced multivitamin may be enough to correct a deficiency, as it was with Scout, but it’s best to work with a healthcare provider to ensure proper diagnosis and treatment.