What Does B12 and Folic Acid Do for Your Body?

November 27, 2025 •

4 min read

According to the NIH, vitamin B12 helps keep the body's nerve and blood cells healthy and helps make DNA. But what does B12 and folic acid do for your body, especially when working together? These two B vitamins form a dynamic duo essential for numerous critical physiological functions, including cell growth, red blood cell formation, and proper nervous system function.

Quick Summary

These two B vitamins are essential for DNA synthesis, red blood cell formation, and nervous system function. They work together to prevent megaloblastic anemia and support cognitive health. Their combined benefits are particularly important during pregnancy and for maintaining overall wellness.

Key Points

Red Blood Cell Formation: Both B12 and folic acid are essential for producing and maturing red blood cells, preventing megaloblastic anemia.
Nervous System Protection: B12 is crucial for maintaining a healthy nervous system and the protective myelin sheath around nerves.
DNA Synthesis and Repair: The vitamins work together in a metabolic pathway to create and repair DNA in every cell of the body.
Homocysteine Reduction: They regulate homocysteine levels in the blood, helping to lower the risk of heart disease and stroke.
Fetal Development: Folic acid is critical for preventing neural tube birth defects in early pregnancy, and B12 supports overall fetal growth.
Masked Deficiency Risk: High folic acid intake can mask the signs of a B12 deficiency, potentially delaying diagnosis and allowing neurological damage to progress.
Synergistic Metabolism: The two vitamins are metabolically intertwined, with B12 needed to help the body effectively use folate.

The Synergistic Partnership of B12 and Folic Acid

Folic acid (Vitamin B9) and Vitamin B12 are not independent agents but rather partners in a critical metabolic process known as one-carbon metabolism. This process is fundamental to life, involved in the synthesis of nucleotides (the building blocks of DNA and RNA), the methylation of various compounds, and the metabolism of certain amino acids. Without adequate levels of both vitamins, this process is hampered, leading to serious health consequences.

One of the most well-known outcomes of this partnership is the prevention of megaloblastic anemia, a condition characterized by abnormally large, immature red blood cells that cannot function properly. Both vitamins are required for the proper maturation of red blood cells. A deficiency in either one can cause this type of anemia.

Core Functions of B12 and Folic Acid in the Body

Both vitamins contribute significantly to overall health, each with specific, indispensable roles.

Vitamin B12 (Cobalamin)

Nervous System Health: B12 is vital for maintaining the health of the nervous system and the creation of the myelin sheath, a protective layer that covers nerves. A deficiency can lead to irreversible neurological damage if not addressed promptly.
DNA Synthesis: It is a key cofactor in the synthesis of DNA, ensuring that the genetic material in every cell is made and repaired correctly.
Energy Metabolism: B12 helps convert food into glucose for energy, though supplements are not a primary energy source for those with adequate levels.

Folic Acid (Vitamin B9)

Fetal Development: Folic acid is most renowned for its role in preventing neural tube defects during pregnancy, such as spina bifida. This is why supplementation is strongly recommended for women who are pregnant or planning to become pregnant.
Cell Growth: It is necessary for cell growth and the healthy functioning of cells throughout the body.
Protein Metabolism: Folic acid works alongside B12 and Vitamin C to help the body break down and create new proteins.

The Critical Link: Homocysteine Metabolism

Perhaps the most crucial metabolic interaction between B12 and folic acid involves homocysteine. High levels of this amino acid are associated with an increased risk of heart disease and stroke. Folic acid and B12 work together to convert homocysteine into methionine, an essential amino acid. Without sufficient levels of both vitamins, homocysteine levels can rise, posing a health risk.

Risks and Considerations

While their combined action is beneficial, an imbalance can cause problems. A high intake of folic acid can mask the symptoms of a vitamin B12 deficiency. This is particularly dangerous because B12 deficiency can cause neurological damage, and if masked by high folate levels, this damage can progress undetected. For this reason, doctors often test for B12 deficiency before prescribing high-dose folic acid supplementation.

Comparing B12 and Folic Acid


Feature	Vitamin B12 (Cobalamin)	Folic Acid (Vitamin B9)
Primary Source	Animal products (meat, fish, eggs, dairy); fortified foods	Leafy greens, citrus fruits, beans; fortified cereals, bread
Absorption	Complex process requiring intrinsic factor protein produced in the stomach	Easily absorbed, especially the synthetic form (folic acid)
Storage in Body	Can be stored in the liver for several years	Water-soluble; must be replenished regularly
Key Role in Nervous System	Crucial for nerve health and myelin sheath formation	Supports brain health but does not have the same neurological protection
Key Role in Pregnancy	Supports overall fetal development, especially brain and nervous system	Critical for preventing neural tube birth defects early in pregnancy
Deficiency Symptom Distinction	Can cause specific neurological symptoms like tingling, numbness, and balance issues	Primarily causes anemia symptoms like fatigue and weakness; neurological issues less common

How to Ensure Adequate Intake

For most individuals, a balanced diet that includes a variety of animal and plant-based foods is sufficient. Vegans and vegetarians, however, must be vigilant about B12 intake, as it is not naturally present in plant foods. In such cases, fortified foods like nutritional yeast, plant-based milk, and cereals are crucial, as are supplements.

For folic acid, many countries, including the United States, fortify grain products like flour, bread, and cereals to help prevent deficiencies, especially in women of childbearing age. Nevertheless, supplements remain a critical component for pregnant individuals or those with specific health conditions.

If you have concerns about your intake or are experiencing symptoms of deficiency, consulting a healthcare provider is essential for accurate diagnosis and treatment. They can recommend a blood test to check your B12 and folate levels and advise on the best course of action, which may include diet modifications or supplementation.

Conclusion

Ultimately, the combined action of vitamin B12 and folic acid is indispensable for maintaining human health. From the fundamental processes of DNA creation and red blood cell production to the intricate functioning of the nervous system and the healthy development of a fetus, these two nutrients work synergistically. While dietary sources are key, understanding their interactions, particularly the risk of high folate masking B12 deficiency, is crucial for safe and effective supplementation. Ensuring optimal levels of both is a cornerstone of preventative health and overall well-being.

Visit the NIH Office of Dietary Supplements for more health information.

Frequently Asked Questions

Yes, B12 and folic acid can be taken together and often are, especially in B-complex supplements or prenatal vitamins. However, it's crucial to ensure you don't have an underlying B12 deficiency before taking high doses of folic acid alone, as it can mask the symptoms of a B12 problem.

A deficiency in either can cause megaloblastic anemia, leading to fatigue, weakness, and paleness. A B12 deficiency can also cause neurological issues like numbness, tingling, and balance problems, while an isolated folate deficiency typically does not.

Individuals following vegan or vegetarian diets are at higher risk for B12 deficiency since it is primarily found in animal products. Older adults, people with digestive issues, and pregnant women also have increased needs or reduced absorption.

B12 is found in meat, fish, eggs, dairy, and fortified cereals. Folic acid (or folate) is abundant in leafy green vegetables, broccoli, asparagus, citrus fruits, and fortified grain products.

They work in tandem to metabolize and lower levels of the amino acid homocysteine. High homocysteine is a risk factor for heart disease and stroke, so keeping it in check is beneficial for cardiovascular health.

Folic acid is critical during the early stages of pregnancy for the development of the fetal brain and spinal cord, and it significantly reduces the risk of major birth defects known as neural tube defects.

Neurological symptoms of B12 deficiency can include tingling or numbness in the hands and feet, memory problems, confusion, and issues with balance and coordination.

Treatment usually involves a combination of dietary changes, oral supplements, or injections for B12 deficiency. If a B12 deficiency is diagnosed, it should be treated before or alongside folic acid supplementation to prevent masking symptoms.