Low folic acid typically results from a combination of factors rather than a single cause. Poor diet is the most common driver, but alcohol use, certain medications, digestive disorders, increased bodily demand during pregnancy, and even how you cook your vegetables all play a role. Isolated folate deficiency is actually uncommon on its own; it usually shows up alongside other nutritional shortfalls.
Diet Is the Most Common Cause
Your body cannot make folate. It depends entirely on what you eat. The richest natural sources are dark leafy greens (spinach, kale, romaine lettuce), legumes (lentils, chickpeas, black beans), asparagus, broccoli, citrus fruits, and liver. Many breads, cereals, and pastas in the U.S. are also fortified with synthetic folic acid. If your diet leans heavily on processed foods and lacks vegetables, your folate intake can fall well below what your body needs.
How you prepare food matters too. Folate is water-soluble and sensitive to heat, so overcooking fruits and vegetables destroys much of the naturally occurring folate before it reaches your plate. Steaming or eating produce raw preserves significantly more than boiling or roasting at high temperatures for long periods.
Alcohol Disrupts Folate at Every Stage
Heavy drinking is one of the strongest risk factors for folate deficiency, and it works through multiple pathways at once. Alcohol blocks absorption of folate in the intestines by suppressing the protein that carries folate across the gut wall. It reduces the liver’s ability to take up and store circulating folate. And it increases folate loss through the kidneys, meaning your body flushes out more than it normally would. On top of all that, people with alcohol use disorder tend to eat poorly, so less folate is coming in while more is going out. The combination makes deficiency almost inevitable with sustained heavy drinking.
Medications That Lower Folate
A surprisingly long list of common medications can deplete your folate levels. Some interfere with absorption, others block the enzymes your body uses to process folate, and still others increase how quickly your body burns through its stores. Medications linked to folate deficiency include:
- Methotrexate, a chemotherapy and autoimmune drug that directly blocks folate metabolism
- Anti-seizure drugs like phenytoin, phenobarbital, and primidone
- Metformin, widely prescribed for type 2 diabetes
- Certain antibiotics, including trimethoprim-sulfamethoxazole and tetracycline
- Oral contraceptives
- Triamterene, a diuretic used for blood pressure
If you take any of these long-term, your doctor may monitor your folate levels or recommend supplementation. The risk increases when multiple medications on this list overlap.
Digestive Conditions That Block Absorption
Even if you eat plenty of folate-rich foods, your body might not absorb it properly. Conditions that damage or inflame the lining of the small intestine, where folate absorption happens, can lead to deficiency despite adequate intake. Celiac disease is a well-known culprit: the immune reaction triggered by gluten damages the intestinal villi responsible for nutrient uptake. Crohn’s disease, particularly when it affects the upper small intestine, has a similar effect. Tropical sprue, short bowel syndrome, and any condition requiring surgical removal of part of the small intestine can also reduce folate absorption significantly.
Pregnancy and Other High-Demand States
Your body’s folate needs rise sharply during periods of rapid cell growth. Pregnancy is the clearest example. A developing fetus requires large amounts of folate for DNA synthesis and neural tube formation, which is why prenatal folate recommendations are substantially higher than those for non-pregnant adults. Breastfeeding continues to increase demand after delivery, since folate passes into breast milk.
Other conditions that speed up cell turnover can drain folate reserves too. Hemolytic anemias, where red blood cells break down faster than normal, force the bone marrow to ramp up production of replacement cells, consuming extra folate in the process. Certain cancers and inflammatory conditions have a similar effect.
The MTHFR Gene Variant
You may have heard that a genetic variant called MTHFR can cause folate problems. The MTHFR gene provides instructions for a protein that helps your body process folate. People with the most studied variant (known as 677 TT) do have slightly lower blood folate levels, roughly 16% lower than people without the variant when both groups consume the same amount. However, the CDC notes that people with an MTHFR variant can still process all types of folate, including synthetic folic acid. Getting 400 micrograms of folic acid daily raises blood folate levels regardless of which MTHFR genotype you carry. So while the variant can contribute to modestly lower levels, it is not a barrier to maintaining adequate folate through diet or supplementation.
Kidney Dialysis
People on hemodialysis lose folate during the filtering process, since folate is a small, water-soluble molecule that passes through the dialysis membrane. The amount lost during a session actually exceeds what a healthy kidney would excrete in urine. That said, research published in Nephrology Dialysis Transplantation found that these losses can be offset by a normal mixed diet containing adequate protein and vegetables. Clinically significant deficiency is relatively rare in well-nourished dialysis patients, though folate supplementation is still common practice in dialysis care because of its role in managing elevated homocysteine levels.
How Low Folic Acid Is Detected
If your doctor suspects folate deficiency, a blood test measures the amount of folate in your serum or plasma. A level above 4 ng/mL is considered normal. Between 2 and 4 ng/mL is borderline. Below 2 ng/mL confirms deficiency. A second test measuring folate inside red blood cells gives a longer-term picture, since red blood cells live for about 120 days. Normal red blood cell folate ranges from 140 to 628 ng/mL. This test is more reliable for identifying chronic deficiency because serum levels can fluctuate with recent meals.
Signs Your Folate May Be Low
Folate deficiency often develops gradually, and early symptoms can be vague enough to dismiss. Persistent fatigue is usually the first sign, since low folate impairs your body’s ability to produce healthy red blood cells, leading to a type of anemia where red blood cells are abnormally large and fewer in number. You might also notice a sore, swollen tongue, mouth ulcers, or a general sense of weakness. As deficiency progresses, some people experience irritability, difficulty concentrating, or tingling and numbness in the hands and feet. Because these symptoms overlap with many other conditions, blood testing is the only way to confirm folate as the cause.