How Does B12 Deficiency Cause Iron-Deficiency Anemia?

If you have low B12 levels or don't get enough iron, you might develop anemia. B12 and iron deficiencies cause different types of anemia, but the symptoms can be similar. Your doctor can test you for low B12 and folate levels, as well as iron, to diagnose or rule out deficiencies or anemia.

Meat is a great source of B12. (Image: Claudia Totir/Moment/GettyImages)

Tip

B12 deficiency does not cause iron-deficiency anemia. B12 and iron are both crucial to red blood cell function, but anemia caused by low B12 is different from iron-deficiency anemia.

What Is Anemia?

The American Society of Hematology estimates that over 3 million Americans have anemia, a blood disorder affecting red blood cells. Red blood cells transport oxygen to your muscles and organs, but people with anemia either don't have enough red blood cells to do this properly, or their red blood cells struggle to transport oxygen.

There are numerous different types of anemia, including iron-deficiency anemia (the most common type), B12-deficiency anemia, sickle cell anemia and aplastic anemia. A lack of B12 and iron are both linked to types of anemia.

What Is B12?

The Linus Pauling Institute at Oregon State University explains that vitamin B12 plays a number of roles in the body, including keeping nerve cells and red blood cells healthy, helping to create DNA, creating neurotransmitters and preserving the myelin sheath around your neurons.

Men and women over 14 years of age should aim to get 2.4 micrograms of B12 per day, the National Institutes of Health (NIH) Office of Dietary Supplements says. That amount increases to 2.6 micrograms during pregnancy and 2.8 micrograms during lactation.

B12 occurs naturally in animal foods, and some foods are fortified with it. The vitamin doesn't occur naturally in plants. Good sources of B12 include meat, fish, poultry, eggs, milk and fortified breakfast cereals. For example, a 3-ounce serving of cooked beef liver provides 60 micrograms of B12 and 215 micrograms folate. A 3-ounce serving of cooked clams provides 84 micrograms of B12 and 25 micrograms folate.

Here's how B12 and anemia are connected. Your body absorbs vitamin B12 through a two-step process. B12 in food is attached to a protein, so first, the hydrochloric acid in your stomach separates the B12 from this protein. Next, the vitamin B12 combines with a new protein, intrinsic factor, and your body absorbs it.

Intrinsic factor is made by stomach lining cells, but some people either don't produce enough intrinsic factor or their body destroys it. As a result, they can't absorb B12 from food or supplements, resulting in a condition called pernicious anemia.

The Role of Iron

UCSF Health describes iron as "an essential element for blood production." Iron helps your body create hemoglobin (a substance in red blood cells that assists with transporting oxygen) and is also present in myoglobin, which transports and stores oxygen in muscles. Iron is also used for respiration, making collagen and metabolizing energy.

The NIH Office of Dietary Supplements recommends the following daily intake of iron for people who aren't vegetarian:

  • 11 milligrams for babies ages 7 to 12 months* 7 milligrams for children ages 1 to 3 years
  • 10 milligrams for children ages 4 to 8
  • 8 milligrams for children ages 9 to 13
  • 11 milligrams for men ages 14 to 18
  • 15 milligrams for women ages 14 to 18
  • 8 milligrams for men ages 19 to 50
  • 18 milligrams for women ages 19 to 50
  • 27 milligrams for pregnant women
  • 9 to 10 milligrams for breastfeeding women* 8 milligrams for adults over 51 years of age

If you're vegetarian or vegan, the recommended daily iron intake is higher. That's because heme sources of iron, found in meat, are more easily absorbed than the nonheme sources of iron found in plant foods.

There are a number of iron-rich foods available. A 3-ounce serving of cooked chicken liver provides almost 10 milligrams of iron, and a 3-ounce serving of beef liver contains 6 milligrams. Three ounces of raw Pacific oysters provides over 5 milligrams of iron. One cup of fortified wheat cereal provides almost 4 milligrams of iron, and one cup of raw spinach provides almost 1 milligram of iron.

Iron-Deficiency Anemia

Iron-deficiency anemia is a condition involving lack of healthy red blood cells due to a shortage of iron in the body. According to the American Society of Hematology, people at an increased risk for iron-deficiency anemia include:

  • Vegetarians and vegans who don't consume enough dietary iron
  • People who menstruate, especially with heavy or long-lasting periods
  • Pregnant or breastfeeding people
  • Anyone who has recently undergone a major surgery or experienced a serious physical trauma
  • People with gastrointestinal diseases that affect iron absorption, like Crohn's disease, peptic ulcer disease or celiac disease
  • People who have undergone gastric bypass or other bariatric procedures

B12 and Anemia

People who have vitamin B12-deficiency anemia — also called megaloblastic anemia — have insufficient healthy red blood cells due to a lack of B12. This type of anemia can also be caused by a lack of folic acid, sometimes called folate.

Johns Hopkins Medicine explains that this type of anemia means that red blood cells don't develop normally. Healthy blood cells should be round, but people with B12-deficiency anemia have larger, oval-shaped red blood cells (and your bone marrow makes less of them). Plus, the red blood cells might die sooner than expected.

You might be at an increased risk of B12-deficiency anemia if you:

  • Have a family history of the condition
  • Have had part of your intestine or stomach removed
  • Suffer from an autoimmune disease
  • Are HIV positive
  • Have been diagnosed with Crohn's disease
  • Eat a vegetarian or vegan diet low in dietary B12

Johns Hopkins says that B12-deficiency anemia and folate-deficiency anemia are difficult to distinguish from each other, so treatment options might combine injections of vitamin B12 and folic acid pills.

Symptoms of Low B12

A doctor can assess low B12 levels through a routine blood test, and the NIH Office of Dietary Supplements says that B12 values below 170 to 250 picograms per millilitre suggest a vitamin B12 deficiency in adults. According to Harvard Health Publishing, symptoms of B12 deficiency can include:

  • Numb or tingling feet, hands or legs
  • Fatigue
  • Feeling weak
  • Trouble walking, such as staggering or struggling with balance
  • Swelling or inflammation in the tongue
  • Memory loss
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