Vitamin D
Vitamin
Also known as: cholecalciferol, D3, ergocalciferol, D2, calciferol
A
Grade A💊 400-4,000 IU daily for maintenance; 1,000-4,000 IU common in supplements🎯 12 primary uses🔗 3 synergiesℹ️ Check contraindications
Levels upNutrition+50 pts
Overview
Vitamin D is a fat-soluble hormone and micronutrient essential for calcium absorption, bone health, immune function, and cellular regulation. Most people have insufficient levels and may benefit from supplementation, particularly those with limited sun exposure.
Primary Uses
Bone healthImmune supportMood regulationMuscle functionVitamin D supplementationVegan vitamin D sourceBone supportImmune functionTestosteroneReproductive hormonesImplantationMale and female fertility
Frequently Asked About Vitamin D
How much Vitamin D should I take?
The typical effective range is 2,000-5,000 IU. Individual needs vary based on age, body weight, diet, and goals — start at the lower end and adjust based on response. Always consult a healthcare provider before starting a new supplement.
When is the best time to take Vitamin D?
Best absorbed with fat-containing meal; timing otherwise flexible. Consistency matters more than perfect timing — pick a daily anchor (e.g. with breakfast or before bed) and stick with it.
Should I take Vitamin D with food?
Recommend with dietary fat for optimal absorption.
Does Vitamin D interact with medications?
Yes — known interactions include Glucocorticoids (reduced vitamin D effectiveness), Anticonvulsants like phenytoin (increased vitamin D metabolism), and Orlistat (reduced fat-soluble vitamin absorption). If you take any prescription medication, talk to your doctor or pharmacist before starting Vitamin D.
What does Vitamin D pair well with?
Vitamin D stacks well with Vitamin K2, Magnesium, and Omega-3s — these combinations either improve absorption or work synergistically toward common goals.
Who should not take Vitamin D?
Vitamin D should be avoided or used with caution by people with Hypercalcemia or conditions causing elevated calcium, Sarcoidosis and certain granulomatous diseases (vitamin D increases calcium absorption), and Concurrent high-dose calcium supplementation (risk of toxicity). Pregnant or breastfeeding women should consult a healthcare provider before use.
What are the side effects of Vitamin D?
Most people tolerate Vitamin D well. The most commonly reported side effects are Minimal at recommended doses and Excessive intake (>10,000 IU chronically) may cause hypercalcemia, nausea, weakness. Side effects are usually dose-dependent — lowering the dose often resolves them.
Dosage
Typical range
400-4,000 IU daily for maintenance; 1,000-4,000 IU common in supplements
Timing
Best absorbed with fat-containing meal; timing otherwise flexible
With food
Recommend with dietary fat for optimal absorption
Dose Tiers
RDA / DV
600-800 IU
Low
400-800 IU
Moderate
1,000-2,000 IU
Optimal
2,000-5,000 IU
Therapeutic
5,000-10,000 IU
Upper Limit
10,000 IU
Duration
Safe for long-term use; fat-soluble so accumulates in body—monitor levels if taking high doses
Special Populations
Older adults (50+) may need higher amounts (600-800 IU minimum); dark-skinned individuals in northern climates need more; pregnant/nursing women should discuss dosing with healthcare provider
Research & Studies
Landmark clinical studies on Vitamin D. Each title links to a plain-English breakdown — what the study shows, what its limitations are, and how to read around them.
- Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data
Individual-participant meta-analysis of 25 RCTs (n=10,933) found vitamin D supplementation reduced risk of acute respiratory tract infection, with greatest benefit in baseline-deficient participants and daily/weekly (not bolus) dosing.
- Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysisTripkovic L, Lambert H, Hart K, et al. · 2012 · American Journal of Clinical NutritionMeta-analysisPubMed ↗
D3 (cholecalciferol) raised serum 25(OH)D significantly more effectively than D2 (ergocalciferol) at equivalent doses, supporting D3 as the preferred form.
- Vitamin D deficiency
Seminal clinical review defining vitamin D deficiency thresholds, recommended 25(OH)D targets for bone and extraskeletal health, and the role of sunlight vs dietary sources.
Browse all curated studies →
Mechanism of Action
- • Acts as a hormone regulating calcium and phosphate absorption
- • Activates vitamin D receptors throughout the body
- • Modulates immune cell differentiation and function
- • Supports muscle protein synthesis
- • Influences neurotransmitter and hormone production
Evidence Quality
Evidence Grade A
Strong RCT evidence supports vitamin D for bone health, immune function, and reducing deficiency. Extensive observational data supports broader health benefits. Recommended by major health organizations.
Safety & Contraindications
Contraindications
- • Hypercalcemia or conditions causing elevated calcium
- • Sarcoidosis and certain granulomatous diseases (vitamin D increases calcium absorption)
- • Concurrent high-dose calcium supplementation (risk of toxicity)
Common Side Effects
- • Minimal at recommended doses
- • Excessive intake (>10,000 IU chronically) may cause hypercalcemia, nausea, weakness
Interactions
💊 Medications
- • Glucocorticoids (reduced vitamin D effectiveness)
- • Anticonvulsants like phenytoin (increased vitamin D metabolism)
- • Orlistat (reduced fat-soluble vitamin absorption)
🧪 Supplements
- • Calcium (synergistic for bone health)
- • Magnesium (needed for vitamin D metabolism)
- • K2 (complementary for bone and cardiovascular health)
Stacking & Synergies
Pairs Well With
Avoid Combining With
High calcium without K2
Best Goal Synergies
Bone healthImmune support
Buying Guide
Standardization Markers
Third-party tested for potency and purityD3 (cholecalciferol) preferred over D2 (ergocalciferol) for efficacyVerified for listed IU content
Practical Notes
- • Test levels before/after
- • Optimal: 40-60 ng/mL
- • Take with largest meal
- • D3 is 87% more effective
- • Consider lichen-derived D3 as vegan alternative
- • Test levels to optimize
- • Always pair with K2
- • Test blood levels
- • Target 40-60 ng/mL for fertility
- • D3 preferred over D2
- • Often deficient in PCOS
- • Test and optimize levels
- • D3 form preferred
- • Must protect eyes
- • Follow device timing exactly
- • Produces natural D plus other compounds
Tags
fat-solublehormone precursorimmunebone healthveganvitaminbonemusclefertilityhormonepregnancypcosinsulinvitamin-dlight-therapyuvbnaturalimmune supportfat-soluble vitaminwell-researcheddeficiency common
Top Products with Vitamin D
Highest-scored catalog products containing Vitamin D, ranked by our scoring engine.
Vitamin D + K2 LiquidThorne96
Vitamin D3 + K2Sports Research95
Grass-Fed Whey Protein IsolateTransparent Labs95
Vitamin D3 K2Transparent Labs95
Related Guides
In-depth guides covering Vitamin D — protocols, comparisons, and use cases.
More in Vitamin
Other ingredients in the Vitamin category.
B-Complex (Energy Focus)
Essential coenzymes for energy metabolism. Methylated forms for optimal function.
Benfotiamine
Fat-soluble thiamine derivative with superior bioavailability. Particularly effective for diabetic neuropathy and AGE reduction.
Beta-Carotene
Provitamin A carotenoid converted to retinol as needed. Cannot cause toxicity. Provides independent antioxidant benefits.
Folate
Essential B vitamin for DNA synthesis, cell division, and methylation. Critical during pregnancy.
Methylfolate
Active form of folate for those with MTHFR variants. Critical for methylation and mood.
Multivitamin (Athletic Formula)
Broad-spectrum insurance for micronutrient gaps. Athletes may need more than RDA.
Last reviewed: September 2026 by the Formulate Research Team. Sources cited above; methodology and scoring criteria published here.
Cite this page
Formulate Research Team. (2026, September). Vitamin D — Evidence-Based Supplement Guide. Formulate Supplement Encyclopedia. https://app.formulate-health.app/learning/supplements/vitamin-d
Educational content based on published research and our scoring methodology. Not medical advice — consult a qualified healthcare provider before starting, stopping, or changing supplements, especially if you take medications, are pregnant, or have a medical condition.