I don't understand the difference/conversion of IU and I.E. when it comes to vitamin D supplements. I have a deficiency so I was prescribed supplements but provided no information as to how long I was supposed to take it to reach normal levels. I have a cousin who is also taking supplements, but he takes 5000 UI a day and I am taking 500 I.E., and finding information about anything measured in I.E. is so much harder than IU for some reason.. His levels were at 15 and mine at 17, so are our recommended intakes similar?