Can anyone send me to a site that explains it in words I can understand? My neuro says she follows a lot of the Mayo /Clininc research and she wants me to go on high doses of Vitamin D. Between amy Calcium+D and multi vitamin I take 1000 IU but she wants me on 5000 IU. What does it do to your tummy, bowels or any other part of your body? Is there any brand that is more reliable? I go to Sams but I can go to Walgreens or CVS