Do you know what your blood levels are? Living in Canada you are not getting much from the sun even in the summer. You pretty much have to be mostly naked and in the sun for 20-30 minutes to get enough and thats below the 49th parallel.
My levels were low even supplementing with 2000 IU a day. I upped it to 4000 and now even to 6000 for the winter and I am in Texas now (was in Calgary) They have done tests with MS patients and have given them tens of thousands of IU's with no side effects. I have heard up to 50,000 IU's with no toxic effects. It is such an important vitamin that I say better safe than sorry.
That said some people have a hard time absorbing what they take. I plan to have a blood test done soon to see if the 6000 is effective.