If you're mildly vitamin D deficient, you would probably want to take an additional 1000 IU per day in addition to the 1000 IU in your multivitamin. It's safe for most people to take up to 4000 IU per day, but unless you've been tested and know you're severely deficient then I wouldn't take more than 2000 IU total per day. Then just keep checking your blood pressure over the next 6 weeks and see what happens.