B9 supports DNA synthesis and cell division, which is why it's especially critical during pregnancy and childhood growth

B9, also called folate or folic acid, is the form your body uses to build and repair DNA. Every time a cell divides—whether that's a red blood cell, a skin cell, or a nerve cell—B9 is there helping to copy the genetic instructions accurately. Without enough B9, cells can't divide properly, which shows up first in fast-growing tissues like blood cells and the cells lining your digestive tract.

The difference between folate and folic acid matters for understanding labels. Folate is the natural form found in food. Folic acid is the synthetic version used in supplements and fortified foods, and your body converts it to the active form. Most people get B9 from both sources without issue, though a small percentage carry a genetic variation that affects how efficiently they process folic acid—something worth discussing with a doctor if you're planning pregnancy or have a family history of neural tube defects.

Key Takeaways

  • B9 is essential for DNA synthesis and cell division, which is why deficiency during pregnancy increases the risk of neural tube defects like spina bifida.
  • Red blood cell formation depends on B9, and deficiency causes a specific type of anemia where cells are larger than normal but fewer in number.
  • Pregnant people and those planning pregnancy need higher B9 intake—typically 400 to 800 micrograms daily—starting before conception.
  • Food sources include leafy greens, legumes, asparagus, and Brussels sprouts, though cooking reduces folate content significantly.
  • Most people in developed countries get enough B9 from fortified grains and varied diet, but certain medications and genetic factors can increase need.

How B9 prevents neural tube defects in pregnancy

The strongest evidence for B9 comes from pregnancy research. Neural tube defects—birth defects of the brain and spine like spina bifida and anencephaly—occur when the neural tube fails to close properly in the first 28 days of pregnancy, often before a person knows they're pregnant. Large randomized trials and decades of observational data show that adequate B9 intake before and during early pregnancy reduces the risk of these defects by 50 to 70 percent.

This is why public health agencies recommend that anyone who could become pregnant take 400 micrograms of folic acid daily, even before conception. If you have a personal or family history of neural tube defects, your doctor may recommend 4,000 to 5,000 micrograms daily starting one month before trying to conceive and continuing through the first trimester. The timing matters: the neural tube closes by week four of pregnancy, so waiting until you see a positive test is too late.

B9's role in red blood cell formation and anemia

B9 works alongside B12 to make red blood cells. When B9 is low, your bone marrow produces fewer red blood cells, and the ones it does make are larger than normal—a condition called macrocytic anemia. You might feel tired, short of breath, or notice pale skin. Unlike iron-deficiency anemia, where cells are small, B9-deficiency anemia shows up as large cells with low numbers.

Certain groups are at higher risk: people taking methotrexate for autoimmune disease, those with celiac disease or Crohn's disease that affects nutrient absorption, and older adults who eat less varied diets. Alcohol use disorder also depletes B9 stores. If you have symptoms of anemia, a blood test can distinguish B9 deficiency from other causes, because the test shows both cell size and B12 levels—B12 deficiency causes the same large-cell pattern.

B9 and homocysteine metabolism

B9, along with B12 and B6, helps your body break down homocysteine, an amino acid produced during normal metabolism. When B9 is low, homocysteine accumulates in the blood. Observational studies have found that people with high homocysteine have higher rates of heart disease and stroke, which led to the hypothesis that lowering homocysteine with B vitamins might prevent cardiovascular disease.

However, randomized controlled trials—the gold standard for testing whether a treatment actually prevents disease—have not shown that B9 supplements reduce heart attack or stroke risk in people with normal B9 levels. This suggests that while B9 does lower homocysteine chemically, lowering homocysteine alone doesn't prevent these events. The takeaway: adequate B9 is important for normal metabolism, but taking extra B9 as a heart-disease preventive in people who aren't deficient is not supported by evidence.

Food sources and how much you need

One cup of raw spinach contains about 145 micrograms of folate. A half-cup of cooked lentils has roughly 180 micrograms. Asparagus, Brussels sprouts, broccoli, avocado, and chickpeas are also rich sources. Fortified breakfast cereals often contain 100 to 400 micrograms per serving. Whole-grain bread and pasta are fortified in most developed countries, which is why widespread B9 deficiency is now rare in these regions.

The recommended daily intake is 400 micrograms for adults. Pregnant people need 600 micrograms, and those breastfeeding need 500 micrograms. Cooking reduces folate content—boiling vegetables can destroy 50 to 75 percent of the folate, while steaming preserves more. If you rely on cooked vegetables, eat a larger portion or include raw leafy greens to meet your target.

Who is at risk for B9 deficiency

Deficiency is uncommon in people eating a varied diet with fortified grains, but certain situations increase risk. Methotrexate, used for rheumatoid arthritis and some cancers, blocks B9 metabolism—people on this drug often take a B9 supplement on days they don't take the medication. Medications that reduce stomach acid, like proton pump inhibitors taken long-term for reflux, can lower B9 absorption. Celiac disease, Crohn's disease, and ulcerative colitis all impair nutrient absorption in the small intestine.

Older adults sometimes develop deficiency because they eat less food overall, have lower stomach acid, or take medications that interfere with absorption. Alcohol use disorder damages the digestive tract and depletes B9 stores. People following strict vegan diets need to may support they're eating enough legumes and fortified plant-based foods, since B9 is less concentrated in plant sources than in animal products like liver (though liver is rarely eaten in modern diets).

Supplements versus food sources

For most people, food provides enough B9. A bowl of fortified cereal, a sandwich on whole-grain bread, and a side salad easily meets the 400-microgram daily target. Supplements become relevant if you're pregnant or planning pregnancy (where 400 to 800 micrograms daily is standard), taking a medication that depletes B9, or have a condition affecting absorption.

Folic acid supplements are absorbed more efficiently than folate from food—about 85 percent versus 50 percent—which is why the recommended dietary allowance accounts for this difference. If you're considering a supplement, a standard prenatal vitamin or a B-complex tablet usually contains 400 to 800 micrograms and costs very little. There's no established upper limit for B9 from food, but very high supplement doses (above 5,000 micrograms daily) can mask B12 deficiency symptoms, which is why it's worth mentioning supplements to your doctor if you're also at risk for B12 deficiency.

Frequently Asked Questions

Can too much B9 from supplements cause problems?

High doses of folic acid supplements can mask the symptoms of B12 deficiency, allowing nerve damage to progress silently. This is rare in people eating animal products, but matters for vegans or older adults. There's no established toxicity level for B9 itself, but doses above 5,000 micrograms daily should be discussed with a doctor, especially if B12 status is unknown.

Do I need a B9 supplement if I eat plenty of leafy greens?

If you're not pregnant and have no absorption issues or medication interactions, food usually provides enough. One cup of raw spinach or a half-cup of cooked lentils gets you close to the daily target. Pregnancy is the main reason to add a supplement, since the need increases and the timing—before you know you're pregnant—makes food alone unreliable.

Does cooking destroy all the folate in vegetables?

Cooking reduces folate but doesn't eliminate it. Boiling causes the largest loss—up to 75 percent—because folate leaches into water. Steaming, microwaving, and stir-frying preserve more. If you cook vegetables, eat a larger portion, include some raw vegetables, or drink the cooking water in soups to recover some folate.

Is folic acid the same as folate?

Folate is the natural form in food; folic acid is the synthetic form in supplements and fortified foods. Your body converts folic acid to the active form your cells use. They're functionally equivalent for most people, though a genetic variation called MTHFR affects how efficiently some people process folic acid—something worth discussing with a doctor if you're planning pregnancy.

Can B9 deficiency cause depression or memory problems?

Low B9 can contribute to neurological symptoms including mood changes and cognitive difficulties, but these are usually accompanied by anemia or other clear signs of deficiency. Observational studies link low B9 to depression, but randomized trials of B9 supplements for depression in people without deficiency have not shown benefit. If you're experiencing mood or memory changes, a blood test can check B9 status as part of a broader evaluation.