Is there a difference between vitamin d and vitamin d-3?

General vs specific: Vitamin d supplements are either vitamin d2 (ergocalcipherol) or vitamin D3 (cholecalcipherol). D2 is plant derived and D3 is animal derived. Some believe they are equivalent to one another, but most vitamin d authorities and studies i've found say that D3 is more bioavailable, which means the body uses it better. There has been an explosion of information about vitamin d in the last 15 years.

Yes: Vitamin d has two forms, d2 and d3. D3 is generally the form that most people benefit from. D2 works as well, but is the plant based form. If you are curious, many labs and doctors now offer the ability to measure your vitamin d level at a reasonable price and you can see if your supplement is working for you. There are lots of crummy supplements out there.