Vitamin B12 and folate (vitamin B9) deficiencies are the most common vitamin-related causes of anemia. Both vitamins are essential for making healthy red blood cells, and when either is missing, the body produces abnormally large, dysfunctional cells that can’t carry oxygen efficiently. But B12 and folate aren’t the only vitamins involved. Deficiencies in vitamins A, C, E, and B6 can also contribute to anemia through entirely different mechanisms.
Vitamin B12 Deficiency: The Most Common Culprit
Vitamin B12 is required for DNA synthesis inside rapidly dividing cells, including the precursor cells that become red blood cells. When B12 is low, these precursor cells can’t divide properly. Their internal components keep maturing, but the nucleus stalls mid-replication. The result is oversized, immature red blood cells called megaloblasts that die before they ever enter the bloodstream. This is called megaloblastic anemia.
B12 deficiency is strikingly common. National surveys across 14 countries have found deficiency rates in women of reproductive age ranging from 3% to over 50%, depending on diet and geography. One study in southern India found that 48% of women were B12 deficient, and vegetarian or vegan women had about 1.5 times the risk of deficiency compared to those who ate meat. That makes sense: B12 is found almost exclusively in animal products like meat, fish, eggs, and dairy.
What sets B12 deficiency apart from other vitamin-related anemias is its neurological effects. Low B12 damages the protective coating around nerves in the spinal cord, a process called demyelination. Early symptoms include tingling and numbness in the hands and feet. If left untreated, this can progress to balance problems, difficulty walking, muscle weakness, and in severe cases, permanent spinal cord damage. Fatigue and general weakness are common at every stage.
Why Some People Can’t Absorb B12
Even with adequate dietary intake, some people develop B12 deficiency because they can’t absorb it. Absorbing B12 from food depends on a protein called intrinsic factor, which is produced by cells lining the stomach. In pernicious anemia, the immune system attacks these cells, shutting down intrinsic factor production and effectively blocking B12 absorption. This is the classic cause of severe B12 deficiency and was historically fatal before its mechanism was understood.
Other absorption problems include stomach surgery (such as gastric bypass), chronic use of acid-reducing medications, and conditions affecting the lower part of the small intestine where B12 is actually taken up. Older adults are particularly vulnerable because stomach acid production naturally declines with age, making it harder to release B12 from food.
For people with absorption issues, treatment typically involves injections to bypass the gut entirely. Patients with severe symptoms or critically low levels (below 100 pg/mL) are generally started on injections to rapidly rebuild stores and prevent irreversible nerve damage. For milder cases or long-term maintenance, high-dose oral supplements at 1,000 micrograms daily have been shown to adequately restore B12 levels, even in people with pernicious anemia, because a small percentage of B12 can be absorbed passively without intrinsic factor.
Folate Deficiency: Same Type of Anemia, Different Risks
Folate plays a nearly identical role to B12 in DNA synthesis. Its primary job is donating chemical building blocks (methyl groups) needed to construct new DNA strands. When folate is low, the same megaloblastic anemia develops: oversized, defective red blood cells that die in the bone marrow before reaching circulation.
In fact, B12 and folate are biochemically intertwined. B12 is needed to recycle folate into its active form. Without B12, folate gets trapped in an unusable state, which is why B12 deficiency can mimic folate deficiency even when folate intake is adequate. This is also why taking high-dose folic acid supplements can temporarily mask B12 deficiency on blood tests while the underlying nerve damage quietly worsens.
The critical difference is that folate deficiency does not cause neurological damage. The numbness, balance problems, and spinal cord changes seen in B12 deficiency are absent. Folate deficiency is particularly dangerous during pregnancy, however, because it dramatically increases the risk of neural tube defects in the developing fetus. Folate is found in leafy greens, legumes, and fortified grains, and many countries now add it to flour and cereal products to prevent deficiency at the population level. Serum folate deficiency (below about 3 ng/mL) is relatively uncommon in countries with fortification programs, running around 3% to 8% in most surveyed populations.
Vitamin A Deficiency: Iron Gets Trapped
Vitamin A deficiency causes anemia through an unexpected mechanism. Rather than reducing iron in the body, it redistributes it. When vitamin A is low, iron accumulates in storage tissues like the liver and spleen instead of being released into the bloodstream where it’s needed for red blood cell production.
The key player here is hepcidin, a hormone that controls how much iron enters circulation. Vitamin A deficiency raises hepcidin levels, which locks iron inside storage cells and prevents it from reaching the bone marrow. The result looks like iron deficiency anemia on a blood test, with low circulating iron and reduced hemoglobin, but giving iron supplements alone won’t fully correct it. This type of anemia requires restoring vitamin A levels so the body can access the iron it already has. Vitamin A deficiency anemia is most prevalent in developing countries where dietary intake of vitamin A-rich foods (liver, dairy, orange and yellow vegetables) is limited, and it often overlaps with infectious diseases that further drive up hepcidin.
Vitamin C and Iron Absorption
Vitamin C doesn’t directly cause anemia in the way B12 or folate deficiency does, but severe deficiency can contribute to it by impairing iron absorption. Plant-based (non-heme) iron needs to be converted to a specific chemical form before the small intestine can absorb it. Vitamin C helps this conversion by creating a more acidic environment in the stomach and keeping iron in its absorbable state.
That said, the real-world impact of vitamin C on iron status is more modest than often claimed. Studies have shown that while adding vitamin C to a single meal can boost iron absorption from that meal, the effect across a full day’s diet is minimal. For people eating a reasonably varied diet, vitamin C status is unlikely to be the limiting factor. Where it matters most is in people who are already at risk of iron deficiency, particularly those eating primarily plant-based diets, where pairing vitamin C-rich foods with iron-rich meals can provide a meaningful boost.
Vitamin E: Protecting Red Blood Cells
Vitamin E acts as an antioxidant that shields red blood cell membranes from oxidative damage. When levels are too low, those membranes become fragile and rupture prematurely, a process called hemolysis. The resulting hemolytic anemia is rare in healthy adults but well documented in premature infants, whose vitamin E stores are naturally low at birth.
Research in premature babies found that red blood cells became significantly more vulnerable to destruction when blood vitamin E levels dropped below 0.6 mg per 100 mL. Supplementation from about 10 days of age reduced this susceptibility. In adults, vitamin E deficiency severe enough to cause anemia typically occurs only alongside fat malabsorption conditions (like cystic fibrosis or certain liver diseases), since vitamin E is a fat-soluble vitamin that requires dietary fat for absorption.
Vitamin B6 and Heme Production
Vitamin B6 is needed to build heme, the iron-containing molecule at the center of hemoglobin. Without enough B6, the body can’t properly assemble heme, and iron begins to accumulate inside developing red blood cells instead of being incorporated into functional hemoglobin. This produces a distinctive pattern called sideroblastic anemia, where iron-laden cells called ring sideroblasts appear in the bone marrow. B6 deficiency as a standalone cause of anemia is uncommon in the general population, but it has been identified as an overlooked cause in hospitalized patients and in people taking certain medications that interfere with B6 metabolism.
How to Tell Which Deficiency Is Causing Anemia
The type and size of red blood cells offer the first clue. Megaloblastic anemia from B12 or folate deficiency produces abnormally large cells (macrocytic anemia), while B6 deficiency and iron-related problems from vitamin A or C deficiency tend to produce small or normal-sized cells. A standard complete blood count will flag this distinction.
From there, blood levels of specific vitamins narrow the diagnosis. B12 levels below 200 pg/mL indicate likely deficiency, though 5% to 10% of deficient patients fall in the 200 to 300 pg/mL gray zone. Serum folate below about 3 ng/mL suggests folate deficiency. When B12 and folate levels are borderline, additional markers like homocysteine (elevated in both deficiencies) and methylmalonic acid (elevated only in B12 deficiency) help distinguish between the two.
Neurological symptoms are a practical differentiator you can notice yourself. If anemia comes with tingling, numbness, or balance issues, B12 deficiency is the most likely cause and should be evaluated urgently, since the nerve damage can become permanent if left untreated for months.