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Vitamin D — Frequently Asked Questions

This content is for informational purposes only and does not constitute medical advice. Consult your healthcare provider before starting any supplement. Full disclaimer

Frequently Asked Questions

How do I know if I am vitamin D deficient?

A simple blood test measuring 25-hydroxyvitamin D (25(OH)D) is the gold standard. Levels below 20 ng/mL (50 nmol/L) indicate deficiency, 20-30 ng/mL is insufficient, and 30-50 ng/mL is considered optimal for immune function. Risk factors for deficiency include dark skin, limited sun exposure, northern latitudes, obesity, and older age. An estimated 42% of US adults are deficient.

Should I take vitamin D3 or D2?

Vitamin D3 (cholecalciferol) is significantly more effective than D2 (ergocalciferol) at raising and maintaining blood 25(OH)D levels. A meta-analysis found D3 was approximately 87% more potent than D2. D3 is the form naturally produced in human skin and has a longer half-life. D2 is plant-derived and suitable for vegans, but requires higher doses to achieve equivalent blood levels.

Do I need to take vitamin K2 with vitamin D?

While not strictly required, K2 is a smart companion to vitamin D, especially at doses above 2000 IU/day. Vitamin D increases calcium absorption from the gut, while K2 (specifically MK-7) activates osteocalcin and matrix GLA protein, which direct calcium into bones and away from soft tissues and arteries. This combination supports both immune and cardiovascular health.

Full Vitamin D Guide

References

  1. (). Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ. DOI
  2. (). Vitamin D and the immune system. Journal of Investigative Medicine. DOI