Vitamin D and Brain Fog
Guideline: Endocrine Society Guidelines; Holick 2007
What Is Vitamin D-Related Brain Fog?
The fog of the indoors. Low vitamin D = neuroinflammation + reduced neurotransmitter synthesis. Your brain has vitamin D receptors throughout — it's not just about bones. Deficiency is extremely common, especially in northern latitudes, darker skin tones, and indoor lifestyles.
What to Do This Week
Seven actionable steps you can start today — free, evidence-based, and designed for when you're foggy.
Body
Get outside during midday when UVB is strongest. Even 10-15 minutes helps.
Food
Fatty fish, eggs, fortified foods. Take any D supplements with a fatty meal.
Water
Standard hydration.
Environment
If you work indoors and live in northern latitudes, supplementation is likely needed.
Connection
Outdoor activities with others combine vitamin D synthesis with social connection.
Tracking
Test levels, supplement, retest in 3 months. Track cognitive symptoms.
Avoid
Don't megadose without testing. Don't take D2 when D3 is available. Don't forget magnesium.
What to Eat: The Vitamin D Supportive Approach
Include vitamin D rich foods and ensure fat intake for absorption.
Sample Day
- breakfast: 2 eggs scrambled in olive oil + handful spinach + slice sourdough + blueberries
- lunch: Big salad (mixed greens, chickpeas, cucumber, tomato, feta, olive oil + lemon) + water
- snack: Apple + handful walnuts or almonds
- dinner: Salmon or chicken thigh + roasted vegetables (broccoli, sweet potato, red onion) + olive oil
- evening: Herbal tea (chamomile or peppermint)
For Vitamin D: Food alone usually can't correct deficiency. Sun exposure and/or supplementation typically needed, especially in northern latitudes.
This is a PATTERN, not a prescription. Adapt to your budget, culture, preferences, and what's available. The principles matter more than perfection: more plants, good fats, less processed food.
When to Seek Urgent Help
STOP — Seek medical evaluation if: sudden onset of cognitive symptoms (hours/days), new focal neurological symptoms, or symptoms don't improve despite normalization of vitamin D levels. These warrant further investigation.
Tests and Investigations
Vitamin D Testing
- 25-OH vitamin D (the primary test)
- Optimal: 40-60 ng/mL (100-150 nmol/L)
- Normal but not optimal: 30-40 ng/mL
- Deficient: <20 ng/mL (50 nmol/L)
Lab 'normal' range often starts at 30 ng/mL. Many practitioners consider 40-60 ng/mL optimal. Below 20 is deficient. Many people with levels 20-30 feel better at higher levels.
Evidence-Based Lifestyle Changes
Sun Exposure
10-30 minutes midday sun, 2-3x/week, with significant skin exposed. Darker skin needs more time.
Evidence: Strong for vitamin D synthesis; limited by latitude, season, skin tone
Vitamin D-Rich Foods
Fatty fish (salmon, mackerel), cod liver oil, egg yolks, fortified foods. Food alone rarely corrects deficiency.
Evidence: Moderate — hard to get enough from food alone
Holistic Support
Test and supplement
Strong — most effective approach
Test 25-OH vitamin D. Supplement D3 based on results. Retest after 3 months.
Pair with magnesium
Moderate — magnesium required for vitamin D activation
200-400mg magnesium daily alongside vitamin D.
Medical Treatment Options
Discuss these options with your prescribing physician. This information is educational, not medical advice.
Vitamin D3 Supplementation
D3 (cholecalciferol), not D2. Dose depends on current level — typically 2,000-5,000 IU daily for maintenance, higher for correction.
Evidence: Strong for correcting deficiency
High-Dose Correction (if severely deficient)
If severely deficient, doctor may prescribe 50,000 IU weekly for 8-12 weeks, then maintenance dose.
Evidence: Strong for rapid repletion
Supplements — What the Evidence Says
Supplements are adjuncts, not replacements for lifestyle changes. Discuss with your healthcare provider.
Vitamin D3
Dose: 2,000-5,000 IU daily for maintenance; higher for correction under guidance
Most people in northern latitudes cannot maintain optimal levels from sun alone, especially in winter.
Magnesium
Dose: 200-400mg daily
Magnesium is required for vitamin D activation. Many people are deficient in both.
Psychological Support and Therapy
Usually not needed specifically for vitamin D. If depression accompanies deficiency, address both — vitamin D alone may not resolve depression.
What People With Vitamin D Brain Fog Say
What Helped
- • Getting tested — I was severely deficient and had no idea
- • Taking D3 with magnesium — made a noticeable difference
- • Higher dose than the standard RDA — therapeutic doses were needed
- • Taking with a fatty meal — improves absorption significantly
What Didn't Help
- • D2 supplements — D3 is more effective
- • Low-dose supplements when severely deficient — needed higher doses
- • Not pairing with magnesium — vitamin D wasn't activating properly
Common Mistakes
- • Assuming you get enough from sun — most people don't, especially in winter
- • Not testing — just supplementing without knowing your level
- • Not taking with fat — vitamin D is fat-soluble, needs fat for absorption
Surprises
- • How common deficiency is — especially in northern climates
- • The brain has vitamin D receptors throughout — it's not just about bones
- • 'Normal' isn't optimal — felt much better at 50 ng/mL than at 30
"Get tested — don't assume your levels are fine. Optimal is 40-60 ng/mL, not just 'normal.' Take D3 (not D2), with a fatty meal, and pair with magnesium for activation. It takes 8-12 weeks to feel the cognitive effects of supplementation."
Quick Reference
Quick Win
Request a 25-OH vitamin D blood test from your doctor. Optimal is 40-60 ng/mL (100-150 nmol/L), not just 'normal' (>30 ng/mL). If low, supplement with D3 (not D2), and pair with magnesium for activation.
Holick, NEJM, 2007; Vitamin D Council