Controversy continues aver the recent Institute of Medicine (IOM) recommended daily allowance for vitamin D versus the amount YOU should take to get vitamin D benefits. Two well-known people in the vitamin D field have weighed in and while you should discuss their opinion with your doctor, the amount they recommended is between 1,000 and 3,000 IU per day.
As usual, the dose answer "depends". For example, if you work outside all day, you get a lot of active vitamin D. If you are not in the sun often, you get little D and may need more in a supplement. Dr. Robert Heany of Creighton University (also happens to be my alma matter), appeared on KETV and talked about the amount he takes. Please remember that vitamin D IS a fat soluable vitamin and can accumulate, so finding a balance is important.
Given the emerging science and elaboration of expert opinion, you may find your doctor recommending at least 1,000 units a day.