My wife had been pushing me to get my Vit. D level checked (her oncologist is requiring her to keep her blood level at around 90 pg/ml), so I had a blood test done. It showed a blood D level of 32 pg/ml. And this was WITH taking 1400 IU per day of Vitamin D3. So I added another 1000 IU.
Please consider more closely Marshall's suggestions to measure both the 25D and 1,25D levels. Likely you are only measuring the 25D levels, as it is easier to measure. The 25D is a precursor, and the 1,25D the active form. If the 1,25D level gets too high, then that suggests that the liver has lost control of 1,25D levels, and you have entered, by this work (which you discredit, I realize) the arena where Vitamin D supplementation is harmful, not helpful.
"Likely you are only measuring the 25D levels, as it is easier to measure. The 25D is a precursor, and the 1,25D the active form." Just checked, and the blood test I took "was" for the 1,25D active form, and not the precursor. Kudos to the lab for using the "right" test.
To add to the data, although I "love" milk, I have developed a sensitivity to it, so no longer drink it other than very sparingly (so no intake of D there). I also don't eat cereals (too much carbohydrate in the AM gives me a hypoglycemic condition later)--so no intake there either. Finally, I live in "the Great Northwest"--and you can imagine what opportunities there are for "solar synthesis" of D during the winter months.
So I think I'm pretty safe with the supplementation.