Hello George,
I took 5000IU daily for about 2 years, and then had a blood test privately - cost of £25, where I took 4 blood spots and sent them off for analysis. The result came back as 161nMol/L. Normal is anywhere between 50 and 220, so I figured I was on the right track, but I did cut back to 2000IU in the summer, as I love being in the sun... back on 5000IU now though! No bone issues, so all is well. I also drink enough soya drink to ensure I have my daily dose of Calcium!
I do agree that the Osteoporosis risk should be pointed out, but also the fact that if one has kidney problems, you should not supplement Vitamin D3 without medical supervision.
Cheers!
Peter