I want to preface this by saying you need to discuss this with your doctor. Have your vitamin D levels checked, if you want to, and go from there.
Lostnomad, I was taking 3,500 IU a day for quite some time but upped it to 4,500 IU a day by my doctor and that is when I noticed the difference.
Alice, I have no idea what my levels were in the beginning. Several years ago I read an article in JAMA (The Journal of the American Medical Association) and they were testing vitamin D on people with heart problems. The results they were getting were so good that they were suggesting to the doctors to recommend that people take 1,000 IU a day. That's when I upped myself from 400 IU to 1,000 IU a day. I am diabetic and am more prone to heart attack and stroke.
about the same time, I was diagnosed with osteoporosis. I was put on medication for that. I was having a lot of pain, too, so my doctor checked my vitamin D levels because vitamin D helps with the absorption of calcium. It was low. He had me raise the amount I was taking to 2,500 IU a day. Several month later he checked the levels again and they were still low so he upped me to 3,500 IU a day. Now, the beginning of the month I was upped again. This is when I noticed the difference. Mind you, I have Crohn's so I have absorption problems. I probably need more than most of the members. That's why it's so important to work with your doctor on this.
I searched the Internet and get various answers to the "normal" range. I saw 30-74 and I saw 40-65. I think my doctor believes the first numbers because he said I was in the normal range now at 33.
Keep in mind, I'm not absolutely positive if it's the vitamin D helping me but it sure would be a coincidence.
Here is a link from WebMD that I found interesting and it helps to explain this even more.
http://www.webmd.com/osteoporosis/news/20080519/supplement-your-knowledge-of-vitamin-d
Sherrine