Vitamin D3

Also known as: cholecalciferol, vitamin d

Grade A — Strong Evidencevitaminfoundational
2000–5000 IUMorning with fat-containing meal

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.

🛡️Immunity😊Mood🧬Longevity💪Muscle & Recovery
Last reviewed: 2026-03-11

Evidence

Grade A

Studies

3

Interactions

3

Forms

3

Evidence Rating: Grade A — Strong Evidence

Multiple high-quality RCTs, systematic reviews, or meta-analyses with consistent findings.

Forms Comparison

Vitamin D3 (Cholecalciferol)

✓ High Absorption

The natural form your skin produces from sunlight. 87% more potent than D2 at raising blood levels.

general supplementationdeficiency correction

Vitamin D2 (Ergocalciferol)

~ Moderate Absorption

Plant-derived form. Less effective at raising and maintaining blood levels than D3.

vegan option

Vitamin D3 + K2 Combo

✓ High Absorption

Combined with K2 (MK-7) to ensure calcium goes to bones, not arteries. The preferred approach.

bone healthcardiovascular protection

Interaction Warnings

Thiazide diureticsModerate

May increase calcium levels excessively

DigoxinModerate

Hypercalcemia from excess D3 potentiates digoxin toxicity

StatinsLow

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 PubMed

Vitamin 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 PubMed

Vitamin 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 PubMed

Alternatives to Consider

These supplements target similar goals and may be worth considering alongside or instead of Vitamin D3.

Vitamin B12

Grade A

Critical for nerve function, DNA synthesis, and red blood cell formation. Vegans, elderly, and metformin users are at high risk of deficiency. Methylcobalamin preferred for neurological benefit.

😊 Mood🧬 Longevity💪 Muscle & Recovery

Omega-3 Fish Oil

Grade A

Essential fatty acids with strong evidence for cardiovascular and mental health. EPA-dominant for mood; triglyceride form for absorption.

😊 Mood🧬 Longevity

Zinc

Grade A

Essential mineral for immune function, wound healing, and testosterone production. Lozenges reduce cold duration by ~33%.

🛡️ Immunity💪 Muscle & Recovery

Related Supplements

Vitamin B12

Grade A — Strong Evidence

Critical for nerve function, DNA synthesis, and red blood cell formation. Vegans, elderly, and metformin users are at high risk of deficiency. Methylcobalamin preferred for neurological benefit.

NAC (N-Acetyl Cysteine)

Grade B — Moderate Evidence

Precursor to glutathione (master antioxidant). Strong evidence for respiratory health, liver support, and psychiatric conditions.

Folate (Vitamin B9)

Grade A — Strong Evidence

Essential for DNA synthesis, methylation, and mood regulation. ~40% of people have MTHFR variants reducing conversion — use methylfolate. Always pair with B12.

Omega-3 Fish Oil

Grade A — Strong Evidence

Essential fatty acids with strong evidence for cardiovascular and mental health. EPA-dominant for mood; triglyceride form for absorption.

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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.

DoseGrade does not sell supplements and has no affiliate relationships with supplement manufacturers.