Vitamin B12, also known as cobalamin, and folate, also known as vitamin B9, are two essential members of the B-complex vitamin family. The B-complex includes eight vitamins that the body needs regularly to support important biological functions.

Vitamin B12 and folate both play important roles in energy metabolism, nervous system health, red blood cell production, and cognitive function. Because these nutrients work closely together in the body, deficiencies in one can sometimes resemble deficiencies in the other.

This article explains the functions of vitamin B12 and folate, common deficiency symptoms, how the two nutrients are connected, and when supplementation with one or both may be considered.

What Is Vitamin B12?

Vitamin B12 is a water-soluble vitamin primarily found in animal-based foods such as red meat, fish, poultry, eggs, and dairy products.

Vitamin B12 supports several important functions in the body, including:

• DNA synthesis
• Red blood cell production
• Nervous system function
• Myelin production, which helps protect nerves
• Energy metabolism

Vitamin B12 absorption becomes more difficult with age because the body may produce less intrinsic factor, a stomach protein required for proper absorption.

For this reason, low vitamin B12 levels are relatively common, particularly in older adults and people with digestive or absorption concerns.

Vitamin B12 Deficiency Symptoms

Early vitamin B12 deficiency symptoms can sometimes be subtle and easy to overlook.

Some people may initially notice:

• Fatigue
• Weakness
• Low energy
• Difficulty concentrating
• Mood changes

As deficiency progresses, symptoms may become more noticeable.

Common symptoms associated with low vitamin B12 levels may include:

• Muscle weakness
• Fatigue
• Irritability or mood changes
• Numbness or tingling in the hands and feet
• Smooth or swollen tongue
• Nausea
• Diarrhea
• Changes in heart rate
• Unexplained weight loss
• Balance or mobility concerns

If you are experiencing symptoms associated with low vitamin B12 levels, it is important to speak with your healthcare provider and request appropriate testing.

What Is Folate?

Folate, also known as vitamin B9, performs several functions similar to vitamin B12.

Folate supports:

• Red blood cell formation
• DNA synthesis
• Cellular growth and division
• Homocysteine metabolism

Homocysteine is an amino acid that may become harmful when levels are elevated over time.

Natural folate is found in foods such as:

• Dark leafy greens
• Beans
• Peas
• Nuts
• Seeds

Many fortified foods also contain folic acid, which is the synthetic form of folate.

Folate is especially important during pregnancy because it helps support healthy fetal neural tube development.

Folate Deficiency Symptoms

Folate deficiency symptoms can closely resemble vitamin B12 deficiency symptoms.

Possible symptoms may include:

• Fatigue
• Weakness
• Pale skin
• Irritability
• Difficulty concentrating
• Shortness of breath
• Numbness or tingling
• Mood changes

Because the symptoms overlap significantly, blood testing is usually necessary to distinguish between the two deficiencies.

In some cases, vitamin B12 and folate deficiencies may occur together.

How Are Vitamin B12 and Folate Deficiencies Diagnosed?

Vitamin B12 and folate deficiencies are typically diagnosed through blood testing.

Healthcare providers may use several tests, including:

• Complete blood count (CBC)
• Peripheral smear (PS)
• Serum vitamin B12 levels
• Serum folate levels
• Methylmalonic acid (MMA) testing
• Homocysteine testing

Both low folate and low vitamin B12 may contribute to macrocytic anemia, a condition characterized by unusually large red blood cells.

Typical findings may include:

• Low hemoglobin
• Low hematocrit
• Elevated mean corpuscular volume (MCV)
• Enlarged red blood cells

General laboratory ranges often include:

• Serum folate below 2 ng/mL may indicate deficiency
• Serum vitamin B12 below 200 pg/mL may indicate deficiency

Additional testing may be recommended when results fall into borderline ranges.

Healthcare providers use combinations of these tests to help determine whether low vitamin B12, low folate, or both are contributing factors.

The Relationship Between Folic Acid and Vitamin B12

Vitamin B12 and folate work together in several important biochemical processes, including the methylation cycle.

The methylation cycle supports functions such as:

• DNA synthesis
• Nervous system function
• Myelin production
• Homocysteine metabolism

When vitamin B12 or folate levels are low, the body may have difficulty producing healthy red blood cells, which may contribute to macrocytic anemia.

Because these nutrients are interconnected, low levels of one may influence how the other functions in the body.

Can High Folic Acid Intake Mask Low Vitamin B12?

Researchers have proposed that high folic acid intake may mask certain signs of vitamin B12 deficiency.

This theory is often referred to as the “methyl trap hypothesis.”

In simple terms, folate may help improve certain blood markers associated with anemia even when vitamin B12 levels remain low. However, neurological symptoms related to low vitamin B12 may still continue if the underlying deficiency is not addressed.

For this reason, it is important to properly identify the cause of deficiency rather than supplementing blindly.

Untreated vitamin B12 deficiency may contribute to long-term neurological complications over time.

Should You Take Vitamin B12 and Folate Together?

Some research suggests that low vitamin B12 combined with high folic acid intake may be associated with elevated homocysteine and methylmalonic acid levels. (3)

Because vitamin B12 and folate work closely together, many healthcare professionals recommend evaluating both nutrients when symptoms of deficiency are present.

Testing helps determine whether supplementation with vitamin B12, folate, or both may be appropriate.

People who use folate supplements may also consider ensuring adequate vitamin B12 intake, particularly if they are older adults, vegetarians, vegans, or have absorption concerns.

What About Food Fortification?

Many foods are fortified with folic acid to help support adequate folate intake in the general population.

While fortification has helped reduce folate deficiency rates, vitamin B12 deficiency remains common because absorption challenges are often the primary issue rather than dietary intake alone.

Vitamin B12 absorption from supplements can occur partly through passive diffusion, which is why higher supplemental amounts are commonly used in vitamin B12 products.

Why Not Natural offers liquid vitamin B12 and B12-folate supplements formulated with methylcobalamin, a bioactive form of vitamin B12.

Takeaway. Understanding Vitamin B12 and Folate Together

Vitamin B12 and folate are closely connected nutrients that support red blood cell formation, nervous system health, DNA synthesis, and energy metabolism.

Because deficiencies in these nutrients may produce similar symptoms, blood testing is often needed to determine whether vitamin B12, folate, or both are low.

People experiencing fatigue, numbness, weakness, mood changes, or anemia-related symptoms should speak with a healthcare provider for appropriate evaluation.

Proper supplementation depends on identifying the underlying deficiency and choosing the right nutrient support for your needs.

You can find Why Not Natural's B12-folate supplement, in an unflavored, bioavailable liquid form with a high dose of B12, here. The Why Not Natural liquid B12 is here.

References