One thing you have to watch out for with vitamin D supplements is if you take the heart medications Diltiazem or Verapamil. There is something about the calcium absorbtion that reduces the effectiveness of these meds.

I take Diltiazem and become D deficient slowly over the year due to lack of sun (that's me, nothing to do with our weather).Under my GP I take D supplement for 3 months at the most while I level out - having interim blood tests for calcium levels. Then I have to stop for the remainder of the year.

Dave.