Comparison guide

Which vitamin D should you take?

All of these raise blood 25(OH)D; they differ in how efficiently, how fast and with what risk. D3 raises levels roughly twice as much as D2 at the same dose, and lichen D3 is the same molecule as standard D3. The benefit is clearest when you are correcting a deficiency, and the biggest practical hazard is stacking products, not the form.

The options, compared

Option	Evidence	Best for	The honest note
Vitamin D3	Strong evidence	Most adults	The best-supported form: it corrects deficiency and, with calcium, reduces fractures in older adults with low levels. 1,000–2,000 IU/day with a meal is a common maintenance dose.	View
Vitamin D2 (Ergocalciferol)	Moderate evidence	Only if D3 is unavailable	Raises 25(OH)D roughly half as efficiently per IU and wears off faster between doses. On older lab assays that under-detect 25(OH)D2, your result can look flat even while you take it faithfully.	View
Vegan Vitamin D3 (Lichen)	Moderate evidence	Vegans and vegetarians	The same cholecalciferol molecule, from lichen instead of sheep's wool, so it beats D2 at raising blood levels; lichen and lanolin D3 have never been compared directly. Check that the capsule shell is plant-based too.	View
Calcifediol (25-OH Vitamin D)	Moderate evidence	Supervised treatment of deficiency	Raises 25(OH)D faster than D3 in most trials, but no outcome advantage has been shown and it can cause hypercalcemia faster if overdosed. It is a prescription medicine in many countries and needs monitoring.	View
Vitamin D3 + K2 Combo	Limited evidence	Convenience, not arteries	The two best trials found no slowing of arterial or valve calcification even at 720 µg/day MK-7, far more K2 than most combos contain. Avoid it on warfarin, and check the D dose, which ranges from 1000 IU to 10,000 IU.	View
Infant Vitamin D Drops	Strong evidence	Every breastfed infant	400 IU/day from the first days of life is one of the few unambiguous recommendations; higher doses added nothing, and the 1,600 IU arm was stopped for excess levels. Read the concentration on the bottle and use only its own dropper.	View

Our verdict

For adults, plain D3 at a modest 1,000–2,000 IU/day with a meal is the default, and lichen-derived D3 is the vegan equivalent — choose it over D2, which is weaker per unit. Calcifediol belongs in supervised clinical situations, and a D3+K2 combo is a convenience rather than a proven upgrade. For breastfed infants, 400 IU/day drops are a clear must, at exactly that dose.