Could Pernicious Anemia Be the Reason You're So Tired?

But fatigue isn't the only pernicious anemia symptom to look for — here's what's up.

Fact: Feeling tired here and there is part of being human. Constant fatigue, however, can be a sign of an underlying health condition — including something called pernicious anemia.

You're probably familiar with anemia, a relatively common condition characterized by a lack of healthy red blood cells that can lead to severe exhaustion, dizziness, and shortness of breath.

Pernicious anemia, on the other hand, is a rare blood disorder in which the body can't properly use vitamin B12, an essential vitamin for healthy red blood cells, according to the National Organization for Rare Disorders (NORD). Similar to anemia, pernicious anemia is mainly characterized by constant fatigue, among other symptoms, but diagnosing pernicious anemia tends to be trickier.

Case in point: Celebrity trainer Harley Pasternak recently opened up about his experience with pernicious anemia. "A few years ago, I was exhausted, and I couldn't figure out what was wrong — I eat well, I exercise, I try and sleep well," he said in an Instagram video. "I had a blood test done, and it showed that I basically had no vitamin B12 in my body," despite regularly eating foods high in B12, explained Pasternak.

After receiving those results, Pasternak said he upped his B12 intake via a variety of supplements, from a B12 spray to B12 tablets. But a subsequent blood test showed that he still "had no B12 in [his] body," shared Pasternak. Turns out, he has pernicious anemia, and the condition was preventing his body from absorbing and using B12, no matter how much he supplemented and ate, he explained.

Below, experts explain everything you need to know about pernicious anemia, from what can cause the condition to how to treat it.

What is pernicious anemia?

Pernicious anemia happens when your body can't make enough healthy red blood cells because it can't use the vitamin B12 you're ingesting, according to the National Heart, Lung, and Blood Institute (NHLBI). Found in milk, eggs, fish, poultry, and fortified cereals, vitamin B12 is essential to maintaining your energy levels.

With pernicious anemia, your body can't absorb enough vitamin B12 from food. In most cases, this happens because your body lacks intrinsic factor, a protein made in the stomach, according to the NHLBI. As a result, you wind up with a vitamin B12 deficiency.

FWIW, other conditions can cause vitamin B12 deficiency, so pernicious anemia isn't a go-to diagnosis if a blood test reveals you have low B12. "Being a vegan and not taking in enough B12 in your diet, having gastric bypass surgery for weight loss, bacterial overgrowth in the gut, medications such as acid reflux medicine, metformin for diabetes, or genetic disorders" can all cause a vitamin B12 deficiency, says Sandy Kotiah, M.D., a hematologist, oncologist, and director of The Neuroendocrine Tumor Center at Mercy Medical Center in Baltimore.

How common is pernicious anemia?

Pernicious anemia is considered a rare condition, so it's difficult to say exactly how many people experience it.

For one thing, there's no "genuine consensus" in the medical community on what counts as a vitamin B12 deficiency, according to the Pernicious Anemia Society (PAS). That said, a 2015 paper published in the journal Clinical Medicine estimates that vitamin B12 deficiency affects at least 3 percent of U.S. adults between 20 and 39 years old, 4 percent of those between 40 and 59 years old, and 6 percent of adults aged 60 and older. Again, though, pernicious anemia is not to blame in all of these cases.

It's also difficult to know how many people have pernicious anemia because the test for intrinsic factor, called the Intrinsic Factor Antibody Test, is only about 50 percent accurate, according to the PAS. This is because roughly half of those with pernicious anemia don't have detectable intrinsic factor antibodies, according to the American Association for Clinical Chemistry.

With all of that in mind, research suggests the condition likely affects just 0.1 percent of the general population and nearly 2 percent of people over 60 years old. So, while it's possible, you shouldn't just jump to assume your own fatigue is caused by pernicious anemia.

Pernicious Anemia Symptoms

Some people with pernicious anemia will have no symptoms, very mild symptoms, or, in some cases, symptoms won't appear until after age 30, according to the National Library of Medicine. It's not totally clear why, but the onset of pernicious anemia is often slow and can span decades, hence why symptoms might not appear until later, according to NORD.

"It can take several years for symptoms to develop, depending on your initial stores of vitamin B12," notes Jack Jacoub, M.D., a hematologist and oncologist, and medical director of MemorialCare Cancer Institute at Orange Coast Medical Center in Fountain Valley, California. "But symptoms are often beyond just fatigue."

Common pernicious anemia symptoms include:

  • Diarrhea or constipation
  • Nausea
  • Vomiting
  • Lightheadedness when standing up or with exertion
  • Loss of appetite
  • Pale skin
  • Shortness of breath, mostly during exercise
  • Heartburn
  • A swollen, red tongue or bleeding gums (aka pernicious anemia tongue)

Over time, pernicious anemia can cause nerve damage and potentially lead to the below additional symptoms, according to the National Library of Medicine:

  • Confusion
  • Short-term memory loss
  • Depression
  • Loss of balance
  • Numbness and tingling in the hands and feet
  • Difficulty concentrating
  • Irritability
  • Hallucinations
  • Delusions
  • Optic nerve atrophy (a condition that causes blurry sight)

Pernicious Anemia Causes

There are a few different things that can lead to pernicious anemia, according to the NHLBI:

  • Lack of intrinsic factor. When you have pernicious anemia, your body makes antibodies that attack and destroy parietal cells, which line your stomach and make intrinsic factor. (Experts say it's not known why this happens.) Without intrinsic factor, your body can't move vitamin B12 through the small intestine, where it's absorbed, and you end up developing a B12 deficiency and, in turn, pernicious anemia.
  • Malabsorption in the small intestine. Pernicious anemia may happen because the small intestine can't properly absorb vitamin B12. That can happen as a result of certain bacteria in the small intestine, conditions that interfere with B12 absorption (such as celiac disease), certain medications, surgical removal of part or all of the small intestine, or, in rare cases, a tapeworm infection.
  • A diet that lacks B12. The NHLBI says diet is a "less common" cause of pernicious anemia, but it does sometimes play a role, particularly for "strict vegetarians" and vegans who don't take a vitamin B12 supplement.

Pernicious Anemia Treatment

Again, diet sometimes plays a role in pernicious anemia, but by and large, treatment won't be effective if you're just eating more vitamin B12 or taking a supplement as that doesn't make the nutrient more bioavailable. "B12 deficiency in pernicious anemia is [usually] caused by autoantibodies preventing adequate B12 absorption in the small intestine," explains Amanda Kaveney, M.D., assistant professor of hematology at the Rutgers University - Robert Wood Johnson Medical School. (

"Trying to overcome a B12 deficiency by taking in more B12 isn't usually going to help because you have a problem with absorption," adds Dr. Jacoub.

Instead, treatment will typically take into account a few different factors, including what's causing your pernicious anemia in the first place, according to the NHLBI. In general, the National Library of Medicine says pernicious anemia treatment usually entails:

  • A monthly shot of vitamin B12; injections of B12 help bypass potential barriers to absorption. (People with severely low B12 levels may need more frequent shots at the beginning of treatment.)
  • Less commonly, some people see success after taking extremely large doses of vitamin B12 supplements by mouth. "There is data to show that if you take a high enough dose of vitamin B12 — 2,000 micrograms [under the tongue], for example — and you absorb a small amount of that dose, that it can fix your vitamin B12 levels," says Dr. Kotiah. (For context, the recommended daily amount of vitamin B-12 is only 2.4 micrograms.)
  • Taking a certain type of vitamin B12 via nasal spray (a method that's been shown to make the vitamin more bioavailable in some cases).

Bottom line: Constant fatigue isn't normal. It might not necessarily be due to pernicious anemia, but regardless, it's worth talking to your doctor about it. They'll likely run some blood tests to try to figure out what's going on, and take things from there.

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