My doctor found that my blood levels of vitamin D were low. She gave me a prescription for 50,000 international units of vitamin D to be taken every two weeks. But Ive read that the recommended dose is more like 1,000 IU a day, and that more than 4,000 IU a day is unsafe. I have thin bones but not osteoporosis yet. Im a healthy woman and dont want to do more harm than good. Whats your advice?