Vitamin D3
Also known as: cholecalciferol, vitamin d
Recommended Dosage
2000–5000 IU
Vitamin D3 (cholecalciferol) is technically a prohormone, not a vitamin. Your skin produces it when exposed to UVB sunlight, but modern indoor lifestyles — especially at northern latitudes — mean widespread deficiency. Research links adequate vitamin D levels to immune function, bone density, mood regulation, and reduced all-cause mortality. It's one of the most universally recommended supplements, particularly for people living above the 37th parallel (roughly north of Los Angeles or Athens).
TL;DR: Essential hormone precursor. Most people in northern latitudes are deficient. Strong evidence for immunity, bone health, and mood.
Evidence Rating: Grade A — Strong Evidence
Multiple high-quality RCTs, systematic reviews, or meta-analyses with consistent findings.
Forms Comparison
Vitamin D3 (Cholecalciferol)
✓ High AbsorptionThe natural form your skin produces from sunlight. 87% more potent than D2 at raising blood levels.
Vitamin D2 (Ergocalciferol)
~ Moderate AbsorptionPlant-derived form. Less effective at raising and maintaining blood levels than D3.
Vitamin D3 + K2 Combo
✓ High AbsorptionCombined with K2 (MK-7) to ensure calcium goes to bones, not arteries. The preferred approach.
Interaction Warnings
May increase calcium levels excessively
Hypercalcemia from excess D3 potentiates digoxin toxicity
May enhance statin effects slightly
⚠️ Important Notes
- Always pair with Vitamin K2 for calcium metabolism
- Get levels tested — toxicity possible at very high doses
- Target serum 40-60 ng/mL
Clinical Evidence (3 studies)
Vitamin D supplementation to prevent acute respiratory infections
Martineau AR et al. (2017) — BMJ
25% risk reduction for acute respiratory infections; individual participant meta-analysis of 25 RCTs
View on PubMedVitamin D and depression: a systematic review
Anglin RE et al. (2013) — Br J Psychiatry
Low vitamin D associated with depression; supplementation may improve symptoms
View on PubMedVitamin D serum levels and upper respiratory tract infections
Ginde AA et al. (2009) — Arch Intern Med
Vitamin D levels inversely associated with URTI in US adults
View on PubMedRelated Supplements
NAC (N-Acetyl Cysteine)
Grade B — Moderate EvidencePrecursor to glutathione (master antioxidant). Strong evidence for respiratory health, liver support, and psychiatric conditions.
Omega-3 Fish Oil
Grade A — Strong EvidenceEssential fatty acids with strong evidence for cardiovascular and mental health. EPA-dominant for mood; triglyceride form for absorption.
Zinc
Grade A — Strong EvidenceEssential mineral for immune function, wound healing, and testosterone production. Lozenges reduce cold duration by ~33%.
Vitamin C
Grade A — Strong EvidenceEssential antioxidant vitamin. Supports immune function, collagen synthesis, and antioxidant defense. 50% infection reduction in athletes.
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⚕️ Important Disclaimer
This information is for educational purposes only. It is not medical advice. Always consult a healthcare provider before starting any supplement regimen, especially if you take medications or have health conditions.
Evidence Stack does not sell supplements and has no affiliate relationships with supplement manufacturers.