# Vitamin D3 (Cholecalciferol)
URL: https://genohealth.app/supplements/vitamin-d3
Type: Supplement
Evidence: Strong evidence
Last reviewed: 2025-06-30

## Intro
Vitamin D3 (cholecalciferol) is the form of vitamin D the body synthesizes in skin from UVB exposure. As a supplement, D3 raises and maintains 25(OH)D levels more efficiently than D2. Most adults need 1000-4000 IU/day to reach functional optimal levels.

## Summary
The form of vitamin D the body makes from sunlight. The right dose depends on your baseline, body weight, latitude — and your VDR genotype.

## Key facts
- Best form: D3 (cholecalciferol)
- Typical dose: 1000-4000 IU/day
- Take with: Fat-containing meal, K2 (MK-7), magnesium
- Time of day: Morning or midday

## Who tends to benefit
- Anyone with 25(OH)D below 30 ng/mL
- Limited sun exposure, indoor work, latitude > 35°
- Darker skin tones (higher melanin reduces cutaneous synthesis)
- Adults over 60 — reduced skin synthesis efficiency
- Higher body weight — vitamin D distributes into adipose tissue

## Dosing notes
- Start with 2000 IU/day if deficient, re-test in 8-12 weeks
- Higher body weight often needs 4000-5000 IU/day to reach optimal range
- Pair with vitamin K2 (MK-7, 90-200 mcg) and 200-400 mg magnesium for proper calcium handling
- Avoid sustained dosing above 4000 IU/day without monitoring

## Genetic context
VDR variants (FokI, BsmI, TaqI) influence how strongly tissues respond to a given 25(OH)D level. Some VDR carriers feel best at the higher end of the optimal range (50-60 ng/mL). CYP2R1 variants reduce conversion to 25(OH)D and can require slightly higher D3 doses.

## Related (knowledge graph)

### Biomarkers
- 25(OH)D (/biomarkers/25-oh-vitamin-d): D3 supplementation reliably raises serum 25(OH)D; expected response 8-12 weeks. [Strong evidence]

### Genes
- VDR (/genes/vdr): VDR variants change how strongly tissues respond to a given vitamin D level; some carriers target the higher end of optimal. [Moderate evidence]

## FAQ
**Q: How much vitamin D3 should I take?**
A: Most adults need 1000-4000 IU/day to maintain 30-50 ng/mL. Body weight, baseline, latitude and VDR genotype all matter — re-testing after 8-12 weeks is the only way to know if your dose is right.

**Q: Do I really need K2 with vitamin D3?**
A: If you're taking more than 2000 IU/day chronically, pairing with vitamin K2 (MK-7) is reasonable. K2 directs calcium toward bone and away from soft tissue.

## Citations
- Tripkovic et al., Am J Clin Nutr 2012 (PMID 22552031): Vitamin D3 raises serum 25(OH)D more effectively than D2.
- Holick et al., J Clin Endocrinol Metab 2011 (PMID 21646368): Endocrine Society guideline on diagnosis and treatment of vitamin D deficiency.

Disclaimer: Informational only — not medical advice.