What is the difference between vitamin D3 and D3?
The experts from Medical News Today cover this very well in their article here.
Most D3 is animal based (sheep) and D2 is plant based. There is a plant based option for D3 (lichens) however it involves an extraction process and is widely known as not being environmentally friendly, sourcing the lichens from the Amazon rainforests.
Absorption and effect on the Kidneys: the D2 variant is often prescribed by doctors to elderly patients who have a lot of burden on their kidneys either because a) they might have chronic kidney disease or b) simply take too many other types of medication putting undue strain on the kidneys. Research shows that Vitamin D2 is easier to process by the kidneys
Much has been made by early research in which certain blood-markers (other substances demonstrating the existence of Vitamin D in the blood stream) were showing that one needs to take less Vitamin D3 than D2 to attain similar levels. However, more recent peer-reviewed research has clearly shown that the bioavailability (the actual useful quantity at cellular level) of Vitamin D2 is similar to D3.