Low folate affects virtually every system that depends on cell growth and DNA repair, which is most of them. Folate, also known as vitamin B9, feeds a metabolic cycle that builds DNA, regulates gene expression, and recycles key amino acids. When levels drop too low, the consequences range from fatigue and a specific type of anemia to serious birth defects, and the causes are more varied than simply not eating enough leafy greens.
What Folate Actually Does
Folate is the hub of what biochemists call one-carbon metabolism, a set of reactions that transfer single carbon units to build and maintain cells. Through this pathway, folate supports the creation of DNA building blocks (purines and thymidine), maintains the balance of several amino acids including methionine, and helps protect cells against oxidative damage.1PubMed Central. One-Carbon Metabolism in Health and Disease One of its most studied jobs is donating the carbon group needed to methylate DNA, a chemical tagging process that turns genes on and off.2PubMed Central. Folate and DNA methylation: a review of molecular mechanisms and the evidence for folate’s role When folate runs short, both DNA production and this gene-regulation machinery slow down, and the tissues that divide fastest, like blood cells and the lining of the gut, are hit first.
Symptoms of Low Folate
The most recognizable sign of folate deficiency is megaloblastic anemia, a condition in which the bone marrow produces abnormally large, immature red blood cells that cannot carry oxygen efficiently. Because DNA synthesis stalls without enough folate, developing red blood cells grow in size without dividing on schedule. The result is fatigue, weakness, shortness of breath, and pale skin. You may also notice a sore tongue, mouth ulcers, or changes in skin pigmentation.
Beyond the blood, folate deficiency has a surprisingly strong connection to mood. People with depression often have lower levels of both serum and red blood cell folate than people without depression. Research has linked the one-carbon cycle, the balance between folate and the amino acid homocysteine, immune function, and even gut health to the regulation of mood, pointing to several pathways through which inadequate folate could contribute to or worsen depressive symptoms.3PubMed Central. Folate and Its Significance in Depressive Disorders and Suicidality: A Comprehensive Narrative Review Irritability, difficulty concentrating, and general cognitive sluggishness are also reported, though these are harder to pin on folate alone because they overlap with so many other conditions.
Why Folate Levels Drop
Your body cannot make folate from scratch, so you depend on dietary intake. The richest natural sources are dark leafy greens, legumes, citrus fruits, and liver. A diet consistently low in fruits and vegetables, which is not uncommon, can lead to deficiency on its own. But diet is only one piece of the puzzle.
Alcohol
Heavy drinking is one of the most potent drivers of low folate. Alcohol disrupts folate at almost every stage: people who drink heavily tend to eat less folate-rich food, and ethanol itself reduces the intestinal and kidney uptake of folate by altering the binding and transport systems that move it into cells. Alcohol also reduces the expression of folate transporters in both the intestine and kidney, compounding the problem.4PubMed. New perspectives on folate transport in relation to alcoholism-induced folate malabsorption–association with epigenome stability and cancer development On top of that, liver storage of folate drops and urinary losses increase, so the body both takes in less and loses more.5PubMed Central. Folate, alcohol, and liver disease Alcoholic liver disease and folate deficiency almost always travel together.
Medications
Several common drug classes lower folate levels. The best known are folate antagonists like methotrexate, used for autoimmune conditions and some cancers, which work precisely by blocking folate’s activity. Pyrimethamine and trimethoprim, both used for infections, operate through a similar mechanism.6PubMed. Drugs and folate metabolism Antiepileptic drugs are another major category. Treatment with carbamazepine, phenytoin, valproate, and several others has been associated with lower serum folate or a higher rate of folate levels falling below the reference range.7PubMed. Antiepileptic drugs interact with folate and vitamin B12 serum levels The exact mechanisms vary and in some cases remain unclear, but the practical takeaway is that if you take any of these medications long-term, your folate status deserves monitoring.
Malabsorption Conditions
Even if your diet is folate-rich, certain gut conditions can prevent you from absorbing it. Folate is mainly absorbed in the upper small intestine, and conditions that damage or inflame that area interfere with the process. Research on celiac disease found that untreated patients have a significantly altered surface environment in the jejunum, making it harder for folate to cross the intestinal wall by the passive diffusion route it normally uses. Crohn’s disease patients showed similar changes.8Gut. Acid microclimate in coeliac and Crohn’s disease: a model for folate malabsorption Inflammatory bowel disease, bariatric surgery, and any condition that shortens or damages the small intestine can have comparable effects.
Genetic Variants
Some people need more folate than others simply because of their genes. The most studied variant involves the MTHFR gene, which codes for a key enzyme in the folate pathway. Carrying the T variant of MTHFR increases your risk of low folate status, especially if your folate intake is also on the low side.9PubMed. The impact of MTHFR 677 C/T genotypes on folate status markers: a meta-analysis of folic acid intervention studies Common gene variants like this one influence how efficiently your enzymes process folate and the downstream products that depend on it.10The Journal of Nutrition. One-Carbon Metabolism–Genome Interactions in Folate-Associated Pathologies This does not mean everyone with an MTHFR variant is deficient, but it does mean the margin for error is smaller.
Neural Tube Defects and Pregnancy
The most dramatic consequence of low folate involves pregnancies. Neural tube defects like spina bifida and anencephaly occur when the neural tube, which forms the brain and spinal cord, fails to close properly during the first few weeks of pregnancy. A lack of folate during this window halts the proliferation and migration of neural tissue during this critical process.11PubMed Central. Spina Bifida Prevention: A Narrative Review of Folic Acid Supplements for Childbearing Age Women Research established in the early 1990s that roughly eight out of ten neural tube defects are attributable to insufficient folate, making them preventable.12PubMed Central. Folic acid and neural tube defects: Discovery, debate and the need for policy change
This discovery led to one of the most consequential public health interventions of the past few decades. In 1998, the United States began requiring enriched cereal grain products to be fortified with folic acid. The result was immediate: the birth prevalence of neural tube defects dropped, and fortification was estimated to prevent roughly 1,000 affected pregnancies per year in the U.S. alone.13PubMed Central. Updated estimates of neural tube defects prevented by mandatory folic Acid fortification – United States, 1995-2011 A meta-analysis of mandatory fortification programs across multiple countries found an overall 44% reduction in neural tube defect risk, with North American programs achieving a 54% reduction and South American programs around 39%.14PubMed Central. The effectiveness of mandatory folic acid fortification compared with pre-fortification periods on reducing neural tube defects (NTDs): a systematic review and meta-analysis Despite this progress, roughly 300,000 cases still occur worldwide each year, largely in countries without mandatory fortification.12PubMed Central. Folic acid and neural tube defects: Discovery, debate and the need for policy change
Because the neural tube closes before most people even know they are pregnant, the standard recommendation is that anyone who could become pregnant should maintain adequate folate intake before conception, not just after a positive test.15PubMed Central. Periconceptional folate deficiency and implications in neural tube defects
Cardiovascular and Brain Health
The link between folate and heart disease centers largely on homocysteine, an amino acid that accumulates when folate is low. Elevated homocysteine has been consistently associated with cardiovascular problems in observational studies. Several studies have reported that folate improves endothelial function, the ability of blood vessel walls to dilate properly, which is a marker for cardiovascular risk. Beyond simply lowering homocysteine, folate may also protect vessels through antioxidant actions and direct interactions with nitric oxide synthase, the enzyme that helps blood vessels relax.16Arteriosclerosis, Thrombosis, and Vascular Biology. Folates and cardiovascular disease
Folate status also matters for the aging brain. A national study of older adults found that those with serum folate deficiency (below 4.4 ng/mL) had a roughly 1.7-fold increased risk of dementia and a nearly 3-fold increased risk of dying from any cause compared to those with adequate levels.17BMJ. Serum folate deficiency and the risks of dementia and all-cause mortality: a national study of old age The proposed explanations include homocysteine-related vascular damage and impaired DNA repair in neurons, making them more vulnerable to oxidative stress. However, that same study noted moderate evidence for reverse causation: early, undetected dementia may lead to poorer nutrition, driving folate levels down rather than the other way around. The relationship is real, but its direction is not fully settled.
The Folate-Cancer Paradox
Folate’s role in cancer is genuinely complicated and worth understanding, because the message is not simply “more is better.” Low folate status appears to increase the risk of certain cancers forming in the first place, likely because inadequate folate leads to DNA that is improperly built and improperly methylated, making mutations more likely. But once a tumor is already established, excess folate supplementation may actually fuel its growth by providing the building blocks that rapidly dividing cancer cells need.18Current Science. Subtype-Specific Folate Dependencies in Colorectal Cancer: Integrating MTHFR Polymorphisms, Consensus Molecular Subtypes, and Tumor Microenvironment Crosstalk This dual nature has been studied most closely in colorectal cancer. The practical implication is that adequate folate intake through diet is protective, but megadosing with supplements, particularly in people with a history of precancerous growths, carries a different risk profile. This is one reason supplementation guidelines exist rather than a blanket “take as much as you want” approach.
When Folate Masks a Vitamin B12 Problem
Folate deficiency and vitamin B12 deficiency cause the same type of anemia, which creates a diagnostic trap. In the 1940s and 1950s, doctors used high-dose folic acid (above 5 mg per day) to reverse the megaloblastic anemia caused by B12 deficiency from pernicious anemia. The blood counts improved, but the treatment masked the underlying B12 deficiency and possibly worsened the nerve damage that B12 deficiency causes.19PubMed Central. Excess Folic Acid and Vitamin B12 Deficiency: Clinical Implications? The anemia looked better on paper while irreversible neurological deterioration continued unchecked. This is why clinicians now generally test for both vitamins when either deficiency is suspected, and why B12 status should be confirmed before attributing anemia to folate alone.
Older adults face a heightened version of this problem. They are more susceptible to both B12 and folate deficiency due to reduced food intake, malabsorption from age-related changes in stomach acid, and poor bioavailability. Making diagnosis harder, the symptoms in elderly patients are often subtle, nonspecific, and highly variable.20Age and Ageing. Vitamin B12 and Folate Deficiency Among Elderly Patients: Is there a window of opportunity? Fatigue and mild cognitive changes in an older person can be dismissed as normal aging when they are actually correctible nutritional deficiencies.
Folic Acid Versus Natural Folate in Supplements
If you look at supplement labels, you will see two main forms: folic acid and methylfolate (often listed as L-5-methyltetrahydrofolate or 5-MTHF). Understanding the difference matters, especially if you carry MTHFR variants. Folic acid is a synthetic compound found in fortified foods and most standard supplements. It has no biological function on its own and must be converted by the enzyme dihydrofolate reductase before your body can use it.21Georgetown Medical Review. The Critical Role of Folate in Prenatal Health and a Proposed Shift from Folic Acid to 5-Methyltetrahydrofolate Supplementation In contrast, 5-MTHF is the predominant natural form of folate found in food and the only form normally circulating in your blood. It is ready for use by cells immediately after you consume it.22PubMed. Folic acid and L-5-methyltetrahydrofolate: comparison of clinical pharmacokinetics and pharmacodynamics
For most people, the conversion of folic acid works fine and standard supplements are effective. But for people with reduced MTHFR enzyme activity, the conversion bottleneck is wider, and taking the already-active 5-MTHF form can bypass that limitation. The 5-MTHF form also avoids the issue of unmetabolized folic acid accumulating in the bloodstream, a phenomenon that occurs when intake exceeds the conversion capacity. Whether unmetabolized folic acid is harmful remains debated, but the availability of the pre-activated form offers a straightforward workaround for those concerned about it.
How Cooking Affects the Folate in Your Food
Even if you eat plenty of folate-rich vegetables, how you prepare them can dramatically change how much folate survives to your plate. Boiling spinach for a typical cooking period destroyed about half the folate, leaving only 49% of what the raw spinach contained. Broccoli fared even worse when boiled, retaining just 44% of its original folate.23British Journal of Nutrition. The effect of different cooking methods on folate retention in various foods that are amongst the major contributors to folate intake in the UK diet The folate leaches into the cooking water. Steaming, on the other hand, caused no significant decrease in folate content for either spinach or broccoli, even at prolonged steaming times. Grilling beef and boiling whole potatoes with the skin on also preserved folate well. The lesson is simple: if you are relying on vegetables to meet your folate needs, steam them or eat them raw when practical.
Gut Bacteria and Folate Production
Your gut microbiome contributes some folate on its own, though probably not enough to rely on. An analysis of over 500 bacterial genomes from the human gastrointestinal tract found that about 13% had all the genes needed for complete folate synthesis from scratch, and another 39% could make folate if supplied with an upstream building block that other gut bacteria or your diet provide.24PubMed Central. Microbial Metabolic Capacity for Intestinal Folate Production and Modulation of Host Folate Receptors Separate research confirmed that bacteria in the upper small intestine do produce folate and that the human host absorbs and uses at least some of it, though the overall contribution to your folate needs remains unclear.25Gastroenterology. Folate synthesized by bacteria in the human upper small intestine is assimilated by the host Interestingly, conditions that slow stomach acid production, including the use of proton pump inhibitors, can promote mild bacterial overgrowth in the small intestine that actually increases local folate synthesis. Whether this meaningfully compensates for other causes of deficiency is an open question, but it is a reminder that the body’s relationship with this vitamin involves more players than just your dinner plate.
Who Is Most Vulnerable
Certain groups face a steeper uphill battle in maintaining adequate folate. People who are pregnant or planning to become pregnant are the most widely discussed, for the neural tube defect reasons covered above. But elderly adults are arguably the most overlooked risk group, because they face a convergence of factors: reduced food intake, impaired absorption, higher rates of medication use, and symptoms that mimic other age-related changes.20Age and Ageing. Vitamin B12 and Folate Deficiency Among Elderly Patients: Is there a window of opportunity? People with alcohol use disorder are at high risk for reasons that go well beyond poor diet, as noted earlier. Anyone on long-term methotrexate, anticonvulsants, or certain antibiotics should have periodic folate monitoring. And people with celiac disease, Crohn’s disease, or other malabsorptive conditions may need higher intake or more bioavailable supplement forms to compensate for what their gut cannot absorb efficiently.
A point worth stressing: folate deficiency rarely announces itself with a single dramatic symptom. It tends to accumulate quietly, producing vague fatigue, mild mood changes, and subtle cognitive shifts that most people attribute to stress or aging. By the time anemia appears on a blood test, levels have often been low for a while. Routine screening is not standard for the general population, which means the people most at risk are often the last to find out.