Vitamin B9

Vitamin B9, known as folate when found naturally in food and folic acid in supplements, is essential for healthy cell function and growth. It’s especially important in processes that involve rapidly dividing cells, such as making red blood cells, repairing DNA, and supporting your body’s ability to produce and regulate genes through a process called methylation.

One of folate’s key roles is in keeping levels of homocysteine in check. Homocysteine is a naturally occurring amino acid that, in excess, can increase the risk of heart disease, stroke, and cognitive decline. Folate, along with vitamin B12, helps convert homocysteine into methionine, a building block for proteins and neurotransmitters. When folate is low, homocysteine levels often rise, a warning sign for long-term cardiovascular and neurological risks.

A lack of folate can also impair the production of healthy red blood cells, leading to a type of anemia called megaloblastic anemia, where cells are too large and inefficient at carrying oxygen. Symptoms of folate deficiency might include fatigue, brain fog, irritability, mouth sores, or even elevated homocysteine on a lab panel. However, folate deficiency usually does not cause nerve damage that’s more typical of a B12 deficiency.

While folate is often discussed in the context of pregnancy because of its protective effects against neural tube defects in early fetal development, its benefits extend well beyond reproductive health. Folate supports cognitive function, DNA stability, and immune resilience for all individuals. It’s particularly important during times of rapid growth, high metabolic demand, or cellular stress.

Dietary sources include leafy greens (like spinach and arugula), legumes, eggs, liver, and fortified grains. Still, many people don’t meet the recommended 400 micrograms (mcg) per day, especially if their diet lacks diversity or includes alcohol, which interferes with folate absorption. Certain medications like methotrexate, antiepileptic drugs, or even long-term aspirin use can also impair folate metabolism.

Supplementation with folic acid can be an effective way to maintain healthy folate levels, especially in at-risk individuals. However, more is not always better. Doses above 1000 mcg per day may mask vitamin B12 deficiency, which can quietly lead to nerve damage if untreated. That’s why it’s important to rule out low B12 before using high-dose folic acid, especially when treating anemia.