What vitamin gets rid of brain fog?

The most likely “brain fog vitamin”: Vitamin B12 (if you’re deficient)

If you’re asking “What vitamin gets rid of brain fog?” the most evidence-backed answer is:

Vitamin B12 can relieve brain fog when brain fog is caused by a B12 deficiency.

B12 deficiency can show up as fatigue and cognitive symptoms—including confusion, poor memory, and feeling mentally “off.” The NIH Office of Dietary Supplements (ODS) lists confusion, dementia, and poor memory among possible symptoms of vitamin B12 deficiency.

What B12-related brain fog can feel like

People often describe it as:

“I’m reading the same paragraph three times.”
“My short-term memory is glitchy.”
“My thinking feels slower than normal.”

Clinically, B12 deficiency can also cause neurological symptoms (like numbness/tingling) and can worsen over time if untreated. (1)

Who is most at risk for low B12?

You’re more likely to have B12-related brain fog if you:

Are over 50 (absorption can drop with age).
Eat little/no animal foods (strict vegetarian/vegan without fortified foods/supplement).
Have absorption issues (e.g., certain GI conditions or surgeries).
Take certain meds long-term (e.g., metformin or acid-reducing medicines), which can contribute to lower B12 over time.

Important reality check: B12 won’t “boost” everyone

If your B12 is already normal, taking extra B12 is unlikely to noticeably sharpen thinking. A large meta-analysis of randomized trials found no evidence that B12 (or B-complex) improves cognitive outcomes in people without overt deficiency. (2)

So the most practical approach is: test first, then target what’s low.

The runner-up vitamin: Vitamin D (mostly via fatigue/mood, not a guaranteed “fog cure”)

Vitamin D is worth checking because low vitamin D can contribute to fatigue and low mood—two things that commonly feel like brain fog.

The NIH ODS notes that vitamin D deficiency in teens/adults can cause osteomalacia, which includes bone pain and muscle weakness—and many people experience general tiredness alongside this.
Cleveland Clinic also describes fatigue and depression among possible effects when vitamin D-related imbalances are severe. (3)

There’s also research linking low vitamin D status with worse cognitive performance in older adults, though this doesn’t prove vitamin D supplements will fix brain fog for everyone. (4)

Don’t mega-dose vitamin D “just in case”

Vitamin D is fat-soluble, and more isn’t always better. The NIH ODS FAQ notes that, unless you’re under medical treatment, adults generally shouldn’t exceed 100 mcg (4,000 IU) per day. (5)

A common non-vitamin cause that mimics brain fog: low iron (especially iron-deficiency anemia)

Iron isn’t a vitamin, but it’s one of the most common “stealth” reasons people feel foggy.

The NIH ODS iron consumer sheet lists symptoms of iron-deficiency anemia that include weakness, tiredness, lack of energy, and problems with concentration and memory.

If your “brain fog” comes with low stamina, shortness of breath on exertion, or heavy periods, iron labs are often a smart add-on to the workup.

The best way to actually clear brain fog: a simple, targeted plan

Step 1: Confirm what’s low (don’t guess)

A clinician may consider labs like:

B12 (sometimes with MMA/homocysteine depending on context)
Vitamin D (25-OH vitamin D)
Iron studies (ferritin, CBC, etc.)
Often also: thyroid, sleep issues, medications, hydration, mood, and stress load

Step 2: Treat the cause, not the vibe

If B12 is low, supplementation (and fixing absorption issues) can be a game-changer.
If vitamin D is low, replacing it to an appropriate level can improve energy for some people.
If iron is low, treating iron deficiency can improve attention and energy.

Step 3: Build habits that make nutrients “work”

Even perfect labs won’t overcome:

chronically short sleep
high stress
nonstop notifications
sedentary days

A surprisingly effective rule: pick one daily “decompression ritual” that reliably lowers mental noise. For some people that’s a walk, stretching, a warm shower, or journaling.

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When brain fog needs urgent medical attention

Seek urgent care if brain fog comes on suddenly or is paired with red flags like:

new weakness/numbness on one side
severe headache
trouble speaking
fainting, chest pain, or severe shortness of breath

Bottom line

Vitamin B12 is the top “brain fog vitamin” when deficiency is the cause. (1)
Vitamin D may help indirectly if low levels are driving fatigue and low mood, but it’s not a guaranteed cognitive fix. (3)
If your nutrient levels are normal, more vitamins usually won’t help—testing + targeted treatment beats guesswork. (2 6)