After quitting smoking 3.5 years ago I suffered from vertigo, balance and cognitive problems, My vit D level was tested at 14.4 ng ml. After supplementation of 50000 iu for a few weeks I noticed some minor improvement. I went onto a maintenance dose of between 2000 a day. My symptoms gradually improved over the next 2 years. I reduced the dosage to 1600 without any noticeable difference for almost a year. My peak vit d level tested at 101 nmol one year ago.When I reduce my dose to 400 iu a day, the balance and vertigo problems return within 24 hours and get worse as time goes on. Unfortunately I get side effects of fluid retention (esp edema in the face) and minor depression and agitation when I take more than 400 IU. Nevertheless, I have been taken 400 iu for almost the past year. Recently the balance and vertigo has become very bad again, so I have tried 800 iu this dramatically improves the balance and vertigo again within 24 hours, but the side effects return.
Can you explain why vitamin d has such an immediate effect (24 hours) on my symptoms and how I can remove the side effects?