What Happens if B12 and Folate Are Low?

December 10, 2025 •

3 min read

According to the National Institutes of Health, deficiencies in vitamin B12 and folate are common causes of megaloblastic anemia. Knowing what happens if B12 and folate are low is crucial for understanding the potential health risks and recognizing symptoms early.

Quick Summary

A deficiency in either vitamin B12 or folate can lead to megaloblastic anemia, which impairs red blood cell production, causing fatigue and weakness. Untreated deficiencies can also result in serious neurological problems and other long-term health complications.

Key Points

Megaloblastic Anemia: Both low B12 and folate cause this condition, leading to fatigue, weakness, and large, immature red blood cells.
Neurological Damage: A key difference is that B12 deficiency can cause irreversible nerve damage, leading to symptoms like numbness, tingling, vision problems, and poor coordination.
Cognitive Issues: Mental and psychological symptoms like memory loss, confusion, and depression are common with deficiencies in either vitamin.
Pregnancy Risks: Folate is critical during pregnancy to prevent neural tube defects in infants, while low B12 also increases this risk.
Causes of Deficiency: Common causes include poor diet (especially vegan), malabsorption disorders (like pernicious anemia, Crohn's), and certain medications.
Treatment is Available: The conditions are treatable with supplements or injections, but early diagnosis is key to preventing permanent damage.

Understanding the Role of B12 and Folate

Vitamin B12 and folate (vitamin B9) are essential B-vitamins vital for red blood cell production and DNA synthesis. Vitamin B12 is also critical for a healthy nervous system. Deficiencies can affect each other; high folic acid can hide a B12 deficiency, letting nerve damage worsen.

Immediate Symptoms of Low B12 and Folate

Initial symptoms are often vague and gradual, sometimes missed. The main issue is megaloblastic anemia, where the body makes large, poor-functioning red blood cells.

Common Symptoms of Anemia:

Extreme fatigue and weakness
Lack of energy
Pale skin
Shortness of breath and dizziness
Headaches and heart palpitations

Other symptoms also occur:

Oral and Digestive Symptoms:

Sore, red tongue
Mouth ulcers
Loss of appetite and weight loss
Diarrhea or other stomach issues

Long-Term and Neurological Complications

Untreated deficiencies can cause severe health problems. B12 is crucial for nerve protection (myelin sheaths). Folate deficiency has risks, especially in pregnancy.

Serious Complications:

Nerve Damage (Neuropathy): Numbness, tingling, particularly in hands and feet.
Cognitive Decline: Memory issues, confusion, mood changes, including depression. Severe B12 deficiency can mimic dementia.
Impaired Coordination: Trouble with balance and walking.
Vision Problems: Blurred or disturbed vision from optic nerve damage.
Heart Conditions: Severe anemia strains the heart, potentially leading to heart failure.
Increased Risk of Cancer: Some links between folate deficiency and certain cancers.
Pregnancy and Birth Defects: Low folate in pregnancy drastically raises the risk of neural tube defects like spina bifida.
Infertility: Temporary infertility is possible, often resolving with treatment.

Comparison of B12 and Folate Deficiencies


Feature	Vitamin B12 Deficiency	Folate (B9) Deficiency
Symptom Onset	Develops slowly, over years, due to large body stores.	Can develop more quickly, within months, as body stores are smaller.
Primary Symptoms	Anemia, neurological problems (paresthesia, gait issues), and cognitive decline.	Anemia, fatigue, mouth sores, and digestive issues.
Key Concern	Permanent nerve and brain damage if untreated.	Neural tube defects in pregnant women if left unaddressed.
Common Cause	Malabsorption issues (e.g., pernicious anemia, gastric surgery), restrictive diets.	Inadequate dietary intake, alcohol abuse, or malabsorption conditions like celiac disease.
Treatment	Injections for absorption issues; oral supplements for dietary causes.	Oral folic acid tablets and dietary changes.

Causes of Deficiency

Deficiencies stem from various factors, not just poor diet.

Causes of B12 Deficiency:

Pernicious Anemia: Autoimmune lack of intrinsic factor needed for B12 absorption.
Dietary Factors: Vegan or vegetarian diets without supplements.
Malabsorption: Intestinal issues like Crohn's or celiac disease, or gastric surgery.
Medications: Metformin and proton pump inhibitors can hinder B12 absorption.

Causes of Folate Deficiency:

Poor Diet: Not enough folate-rich foods.
Malabsorption: Digestive issues.
Alcohol Abuse: Interferes with folate use.
Increased Need: Pregnancy, certain cancers, hemolytic anemia.

Conclusion: The Importance of Addressing Deficiencies

Low B12 and folate impact red blood cells, nerves, and overall health. From fatigue and paleness (megaloblastic anemia) to serious nerve damage, prompt treatment is vital. Regular checks and treatment, including supplements or injections, prevent long-term issues. High-risk groups like vegans, older adults, or those with certain conditions need proactive screening and supplementation.

Disclaimer: This article is for informational purposes only and does not constitute medical advice. Consult with a healthcare professional for diagnosis and treatment. [^1.1]

Frequently Asked Questions

Megaloblastic anemia is a blood disorder caused by a deficiency of either vitamin B12 or folate. It results in the bone marrow producing abnormally large, immature, and dysfunctional red blood cells, leading to a reduced ability to carry oxygen throughout the body.

Yes, if a vitamin B12 deficiency is left untreated for a long time, it can cause severe and potentially permanent neurological damage. This can manifest as persistent numbness or tingling, balance issues, and memory problems.

Folate is critical during early pregnancy for the proper formation of the fetus's brain and spinal cord. Inadequate folate levels can lead to serious birth defects known as neural tube defects, such as spina bifida.

While both can cause megaloblastic anemia with similar symptoms like fatigue, B12 deficiency is more specifically linked to nervous system issues. Folate deficiency symptoms can appear more quickly, sometimes within weeks, unlike B12 deficiency, which can take years to show.

Yes, people following a strict vegan or vegetarian diet are at a higher risk of B12 deficiency because this vitamin is primarily found in animal products. These individuals often need to take supplements or consume fortified foods.

Treatment varies depending on the cause. B12 deficiency may require injections, especially if there are absorption issues like with pernicious anemia. Folate deficiency is typically treated with oral folic acid tablets.

Doctors check for B12 deficiency before prescribing folic acid because supplementing with folate can mask an underlying B12 deficiency. If B12 levels are low, adding folate can correct the anemia symptoms while allowing neurological damage to progress undetected.