Folate (vitamin B9) is one of those nutrients you rarely think about until it’s low. Folate matters because it helps your body make DNA and build healthy red blood cells,while also supporting key chemical pathways involved in metabolism. When folate runs low, the effects can feel surprisingly whole-body.
What folate deficiency can do
The classic medical picture is megaloblastic anemia, where red blood cells are larger than normal and do a worse job delivering oxygen. That can translate into fatigue, weakness, shortness of breath, dizziness, paleness, and heart palpitations.
Folate deficiency can also show up in places people don’t always connect to a vitamin issue. Some notice mouth changes like a sore, red tongue or mouth ulcers.
Others feel it more “up top,” with symptoms like trouble focusing, memory lapses, mental sluggishness, or feeling unusually irritable. Mood changes can overlap too, including low mood or feeling more on edge than normal.
How to spot it
Start with pattern recognition, not self-diagnosis. Folate deficiency is less common in countries with folic acid fortification, but it still happens. Risk tends to go up if you have one or more of these:
- a diet consistently low in folate-rich foods
- heavy alcohol use
- digestive or absorption issues (like celiac disease or Crohn’s disease)
- dialysis
- certain blood disorders (like hemolytic anemia)
The most practical way to confirm it is lab work. Clinicians typically look at:
- CBC and MCV (to check for macrocytosis and anemia)
- Serum folate
- Vitamin B12 (because the two deficiencies can look similar and can coexist)
One quick lab note: serum folate is usually the best first test. According to the College of American Pathologists, RBC folate tests aren’t routinely recommended because they often don’t change the diagnosis and can be more variable.
How to fix it
The goal is simple: restore folate levels and address the why so it doesn’t keep happening.
Food first (plus fortification): Folate is naturally found in legumes, leafy greens, and citrus, and folic acid is added to many grain products in the U.S. and other countries. If diet quality or alcohol intake is the main driver, fixing that is part of the treatment.
Supplements that actually replenish stores: For folate deficiency anemia, the NHS notes that treatment is typically daily folic acid tablets for about 4 months (longer if the underlying cause persists). In real life, dosing is individualized based on severity, cause, and clinician preference.
Do not skip the B12 check: This matters. Folic acid can improve the anemia so well that it masks an underlying B12 deficiency, while neurologic damage from B12 deficiency can continue. Most guidance explicitly recommends checking B12 before starting folic acid for this reason.
How fast will you feel better? Lab response can begin quickly. Blood testing is sometimes done around 7–10 days after starting treatment to assess response. Symptom improvements often lag behind labs, especially if you have been depleted for a long time or have ongoing triggers.
What it doesn’t do
Correcting folate deficiency can be a big deal, but it is not a universal cure for brain fog, anxiety, or low mood. If symptoms are driven by sleep issues, thyroid problems, iron deficiency, medication effects, chronic stress, or primary mood disorders, folate alone will not solve the root cause.
If you’ve been stuck in that tired-and-foggy groove for a while, folate is worth checking. A few basic labs can tell you if it’s actually low, and if it is, it’s usually very fixable with the right supplement plan plus a few diet tweaks.