What are the sources of vitamin d3?

The best is the sun : I give all of my patient 2000iu of d3 daily not kids i give the 1000iu if older than 4.

It's the sources.: The major sources of vitamin D3 are dairy and sun exposure. Now, we generally tell people to avoid the sun because of its effects on the skin and development of cancer. And not everyone tolerates dairy so well, or even likes dairy. This is why vitamin D deficiency is so rampant. So the supplements of D3 have become useful sources.