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Types of Vitamin D: Forms & Bioavailability

Evidence:Strong
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This content is for informational purposes only and does not constitute medical advice. Statements about dietary supplements have not been evaluated by the FDA and are not intended to diagnose, treat, cure, or prevent any disease. Individual results may vary — consult your healthcare provider before starting any supplement. Full disclaimer

Forms Comparison

FormBioavailabilityBest For
Vitamin D3 (Cholecalciferol)HighStandard supplementation — most effective form for raising blood levels; take with fat
Vitamin D3 Liquid DropsHighFlexible dosing — easy to adjust dose; can add to food or drinks
Vitamin D3 + K2 CombinationHighComprehensive support — K2 directs calcium to bones and away from arteries
Vitamin D2 (Ergocalciferol)ModerateVegan option — plant-derived but less effective at raising 25(OH)D than D3

Vitamin D3 (Cholecalciferol)

Bioavailability: High. Best for: Standard supplementation — most effective form for raising blood levels; take with fat.

Vitamin D3 Liquid Drops

Bioavailability: High. Best for: Flexible dosing — easy to adjust dose; can add to food or drinks.

Vitamin D3 + K2 Combination

Bioavailability: High. Best for: Comprehensive support — K2 directs calcium to bones and away from arteries.

Vitamin D2 (Ergocalciferol)

Bioavailability: Moderate. Best for: Vegan option — plant-derived but less effective at raising 25(OH)D than D3.

Full Vitamin D Guide

References

  1. Meta-analysisMartineau AR, Jolliffe DA, Hooper RL, et al. (2017). Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ. DOI PubMed
  2. ReviewAranow C (2011). Vitamin D and the immune system. Journal of Investigative Medicine. DOI PubMed
  3. Meta-analysisKawada K, Sato C, Ishida T, Nagao Y, et al. (2025). Vitamin D Supplementation and Allergic Rhinitis: A Systematic Review and Meta-Analysis.. Medicina (Kaunas, Lithuania). DOI PubMed
  4. Wang R, Xu F, Xia X, Xiong A, et al. (2024). The effect of vitamin D supplementation on primary depression: A meta-analysis.. Journal of affective disorders. DOI PubMed
  5. Fang A, Zhao Y, Yang P, Zhang X, et al. (2024). Vitamin D and human health: evidence from Mendelian randomization studies.. European journal of epidemiology. DOI PubMed
  6. Musazadeh V, Keramati M, Ghalichi F, Kavyani Z, et al. (2023). Vitamin D protects against depression: Evidence from an umbrella meta-analysis on interventional and observational meta-analyses.. Pharmacological research. DOI PubMed
  7. Formisano E, Proietti E, Borgarelli C, Pisciotta L (2023). Psoriasis and Vitamin D: A Systematic Review and Meta-Analysis.. Nutrients. DOI PubMed
Show 5 more references
  1. Meta-analysisYeung WG, Palmer SC, Strippoli GFM, Talbot B, et al. (2023). Vitamin D Therapy in Adults With CKD: A Systematic Review and Meta-analysis.. American journal of kidney diseases : the official journal of the National Kidney Foundation. DOI PubMed
  2. Meta-analysisWilliamson A, Martineau AR, Sheikh A, Jolliffe D, et al. (2023). Vitamin D for the management of asthma.. The Cochrane database of systematic reviews. DOI PubMed
  3. Tamblyn JA, Pilarski NSP, Markland AD, Marson EJ, et al. (2022). Vitamin D and miscarriage: a systematic review and meta-analysis.. Fertility and sterility. DOI PubMed
  4. Abboud M (2022). Vitamin D Supplementation and Sleep: A Systematic Review and Meta-Analysis of Intervention Studies.. Nutrients. DOI PubMed
  5. Palacios C, Kostiuk LK, Pena-Rosas JP (2024). Vitamin D supplementation for women during pregnancy.. The Cochrane database of systematic reviews. DOI PubMed