Vitamin D2 and Vitamin D3 are not the same, and definitely not equal. D2 and D3 are similar pre-hormones, but different. D2 (Ergocalciferol) is the plant version. D3 (Cholecalciferol) is the animal version.
Both pre-hormones need to be converted to their active hormone form in the kidney. D2 (plant version) will work in us but only lasts 2-3 days. D3 (animal version) lasts for 2-3 weeks. That huge difference makes a huge difference in dosage needs.
If you are low in your 25-hydroxy Vitamin D level (blood test), which version you use determines how much you need to take for how long. I always use D3 for my patients. This avoids confusion. D3 is cheaper and you need less of it. Many people who use D2 to correct a low level need to start all over after a few months.
Most patients in Iowa need close to 2000 units of D3 daily. That is 10,000 to 15,000 units of D3 per week. I personally use 2 or 3 capsules of 5000 units each week. This is cheap and easy. The same dose in D2 is at least 50,000 units each week!
I recommend that you use D3 whenever possible.
Why are we talking about Vitamin D3 supplements a few days before the winter Solstice, when the sun is lowest in the sky? In Northern Iowa, since mid-September, I have gotten no Natural Vitamin D from Sunshine. It will be April before I get any. For now, I need Vitamin D3 supplements.
Jay Ginther, MD