Folate deficiency is a condition where your body doesn’t have enough folate (vitamin B9) to carry out essential processes like building DNA, producing red blood cells, and regulating gene activity. It’s diagnosed when serum folate drops below 3 ng/mL or red blood cell folate falls below 100 ng/mL. Because folate is involved in so many basic cellular functions, a deficiency can affect everything from your energy levels to your cardiovascular health, and during pregnancy it poses serious risks to fetal development.
What Folate Does in Your Body
Folate is a one-carbon donor, which is a technical way of saying it supplies a small but critical chemical building block that dozens of reactions in your body depend on. The two most important jobs are DNA synthesis and methylation. During DNA synthesis, folate helps produce one of the four “letters” in your genetic code. When folate is scarce, cells can accidentally substitute the wrong molecule into DNA strands, triggering repair attempts that increase the frequency of chromosomal breaks.
Methylation is the process your body uses to switch genes on and off, produce neurotransmitters, and process fats. Folate feeds into this system by helping convert an amino acid called homocysteine into methionine, which then becomes the body’s main methyl donor. When folate levels drop, homocysteine builds up instead. Even mildly elevated homocysteine (around 15 micromoles per liter) is independently associated with increased risk of cardiovascular disease, because homocysteine and its byproducts damage blood vessel walls.
Symptoms of Folate Deficiency
The earliest signs are often vague: fatigue, irritability, and difficulty concentrating. These show up because folate-starved cells can’t divide efficiently, and red blood cell production slows down. As the deficiency worsens, it leads to megaloblastic anemia, a condition where the bone marrow produces abnormally large, immature red blood cells that can’t carry oxygen properly. That’s when fatigue becomes more severe and you may notice shortness of breath, pale skin, and heart palpitations.
Other physical signs include glossitis (a swollen, sore tongue that may look unusually smooth and red), mouth sores, and changes in skin or hair pigmentation. Some people experience digestive symptoms like diarrhea or reduced appetite. Mood changes, including depression, can also occur because folate is involved in producing neurotransmitters like serotonin.
Common Causes
Most folate deficiency comes down to three categories: not eating enough, not absorbing enough, or using it up too fast.
- Low dietary intake is the most straightforward cause. People who eat few vegetables, legumes, or fortified grains are at higher risk, as are those with alcohol use disorder, since alcohol interferes with folate absorption and increases how quickly the body excretes it.
- Malabsorption conditions include celiac disease, inflammatory bowel disease, tropical sprue, and short bowel syndrome. Bariatric surgery, particularly gastric bypass, also reduces folate uptake. Even low stomach acid can hinder absorption.
- Medications are an underappreciated cause. Methotrexate (used for autoimmune conditions and certain cancers) directly blocks folate metabolism. The seizure medication phenytoin, the antibiotic trimethoprim, and sulfasalazine (used for IBD and rheumatoid arthritis) all interfere with folate utilization or speed up its breakdown.
- Increased demand occurs during pregnancy, breastfeeding, and periods of rapid growth. Conditions that cause high cell turnover, like certain blood disorders, also deplete folate stores faster than normal.
The MTHFR Gene and Folate Processing
Your ability to use folate depends partly on a gene called MTHFR, which produces an enzyme that converts folate into its active form (5-MTHF). Some people carry a variant of this gene, most commonly called C677T, that reduces the efficiency of this conversion. If you have this variant, standard folic acid from supplements or fortified foods may not convert well, potentially leading to a buildup of unused folic acid alongside functionally low active folate.
People with MTHFR variants often have elevated homocysteine levels even when their folate intake seems adequate. For these individuals, supplementing with the already-active form of folate (sometimes labeled as L-methylfolate or 5-MTHF) may be more effective than standard folic acid, though this is something to discuss based on your specific blood work.
Folate Deficiency During Pregnancy
The stakes of folate deficiency are highest in early pregnancy. The neural tube, which becomes the brain and spinal cord, folds and closes during the third and fourth weeks of pregnancy, often before a person even knows they’re pregnant. If folate is insufficient during this window, the tube may not close properly, leading to neural tube defects.
The most common of these are spina bifida, which affects about 1,300 babies per year in the United States, and anencephaly, which affects about 700. Encephalocele, a rarer defect where brain tissue protrudes through the skull, affects roughly 350 babies annually. This is why public health guidelines recommend that anyone who could become pregnant maintain adequate folate intake before conception, not just after a positive pregnancy test.
How It Differs From B12 Deficiency
Folate deficiency and vitamin B12 deficiency look similar on a blood test because both cause megaloblastic anemia. The critical difference is neurological damage. B12 deficiency causes demyelination of the spinal cord, leading to numbness, tingling, balance problems, and in severe cases, irreversible nerve damage. Folate deficiency generally does not cause this kind of nerve deterioration.
This distinction matters because taking folic acid supplements can mask a B12 deficiency. The anemia improves on blood tests, but the neurological damage continues silently. In fact, high doses of folic acid can reduce the active fraction of B12 in the blood, worsening the underlying deficiency. Cases have been documented where folic acid supplementation actually accelerated neurological decline in people with undiagnosed pernicious anemia. This is why it’s important to check both folate and B12 levels, not just one.
Best Dietary Sources of Folate
The recommended daily intake for adults is 400 mcg of dietary folate equivalents (DFE). Pregnant individuals need 600 mcg. Some of the richest sources per serving:
- Beef liver (3 oz, braised): 215 mcg, over half the daily value
- Spinach (½ cup, cooked): 131 mcg
- Black-eyed peas (½ cup, cooked): 105 mcg
- Fortified breakfast cereal (1 serving): 100 mcg
- Asparagus (4 spears, cooked): 89 mcg
- Brussels sprouts (½ cup, cooked): 78 mcg
- Romaine lettuce (1 cup, shredded): 64 mcg
- Avocado (½ cup, sliced): 59 mcg
- Broccoli (½ cup, cooked): 52 mcg
In the United States, white flour, rice, pasta, and many cereals are fortified with folic acid (the synthetic form of folate). A single slice of white bread provides about 50 mcg. This mandatory fortification program, introduced in 1998, is one reason severe folate deficiency is less common in the U.S. than in countries without similar policies. Still, people who eat mostly unfortified whole grains, follow restrictive diets, or have absorption issues may not get enough from food alone.
Treating a Deficiency
Folate deficiency is typically treated with oral folic acid supplements, and most people see blood levels improve within a few weeks. The body doesn’t store large amounts of folate, so if the underlying cause persists (a malabsorption condition, ongoing medication use, or chronically low dietary intake), supplementation needs to continue long-term.
If you have a condition that impairs absorption, such as celiac disease or inflammatory bowel disease, treating the gut condition itself often improves folate uptake. For people on medications that interfere with folate metabolism, a healthcare provider may prescribe supplemental folate alongside the medication. People with known MTHFR variants may benefit specifically from L-methylfolate rather than standard folic acid, since their bodies have difficulty making that conversion on their own.
One important note: because folate and B12 metabolism are closely linked, correcting a folate deficiency without checking B12 can allow hidden nerve damage to progress. Both levels should be assessed together, particularly in older adults and anyone with neurological symptoms like tingling or numbness in the hands and feet.