B12 and Folate: Nerve and Blood Health

B12 and Folate — Partners in the Body

Vitamin B12 (cobalamin) and folate (folic acid) are two B-group vitamins that are biochemically intertwined. They work together in a process called methylation — a fundamental cellular mechanism that modifies DNA, produces neurotransmitters (such as serotonin and dopamine), processes hormones and clears a potentially harmful compound called homocysteine.

In plain terms: without B12 and folate, many cellular processes stall.

Nerve Health: B12 and Myelin

B12 is essential for producing myelin — the fatty protective sheath around nerve fibres that allows nerve impulses to travel quickly and accurately. When B12 is deficient, myelin begins to break down.

Symptoms can include: tingling or numbness in the hands and feet, unsteady gait, muscle weakness, memory problems and difficulty concentrating — what is commonly described as "brain fog". What makes this dangerous is that these symptoms can appear before blood markers change — meaning a normal complete blood count does not rule out B12 deficiency.

Left untreated for too long, nerve damage can become irreversible (B12 Deficiency — StatPearls, 2024). Early detection pays dividends.

Blood Formation: Megaloblastic Anemia

Deficiency of either B12 or folate disrupts the maturation of red blood cells in the bone marrow. The cells become abnormally large and ineffective — this is called megaloblastic anemia. Symptoms resemble those of other anemias: fatigue, pale skin and shortness of breath.

A critical nuance: folate supplementation can "mask" the anemia of B12 deficiency — it will improve the blood picture, but neurological damage continues. This is why doctors always test both markers together.

Folate: Pregnancy and DNA

Folate is required for DNA synthesis and cell division — especially in rapidly dividing tissues. During pregnancy this is particularly critical: the neural tube (from which the brain and spinal cord develop) closes within the first 3–4 weeks after conception. Folate deficiency during this window increases the risk of neural tube defects such as spina bifida.

For this reason, folate supplements are recommended for all women who are planning a pregnancy — not only after a positive test, but before conception.

Who Is at Risk of Deficiency

B12 deficiency risk groups:

• Vegans and vegetarians — B12 is virtually absent from plant foods. Animal products (meat, fish, eggs, dairy) are the primary sources. A vegan who does not supplement or eat fortified foods will inevitably develop deficiency — the only question is when.

• Older adults — stomach acid production declines with age, and absorbing B12 from food requires acid. The production of "intrinsic factor" — the protein needed for B12 absorption in the small intestine — also falls with age, regardless of diet.

• People taking certain medications — metformin (used for diabetes) and PPIs (proton pump inhibitors for heartburn) reduce B12 absorption with long-term use.

• Atrophic gastritis — an inflammatory stomach condition that damages the cells which produce intrinsic factor and acid.

Folate deficiency risk groups:

Folate deficiency is less common thanks to food fortification and broad dietary availability — green leafy vegetables, beans, lentils and broccoli are rich sources. However, the following groups are at risk: pregnant women (increased demand), regular alcohol users (alcohol impairs folate absorption), and users of certain medications such as methotrexate.

Methylation and Homocysteine

Both vitamins participate in processing homocysteine — an amino acid. When either is deficient, homocysteine accumulates in the blood. Elevated homocysteine is associated with a higher risk of cardiovascular disease and dementia. It is important to understand, however, that this is an observational association, not a proven causal relationship.

What to Do in Practice

If you belong to a risk group or experience the symptoms described above, request a blood test. B12 and folate levels are measured with a simple panel. One important caveat: symptoms and lab values do not always align — some people have pronounced neurological signs while their lab levels appear borderline normal. The overall clinical picture and trends over time matter more than a single number.

If you follow a vegan diet, B12 supplementation is not optional — it is a necessity.