Supplemental vitamin D needs to be an oil-based D3, *not* D2 and not in dry tablet form. Carlson Ddrops is a good brand (it raised my kids' and my levels well, verified by blood tests; I have no vested interest in them other than being a very satisfied customer
).
Blood test for level should be the 25-hydroxy vitamin D. (Double-check the name of the test; there is another test called the 1,25 dihydroxy which is *not* good for assessing whether your vitamin D level is adequate.)
On the amount to supplement, medical literature shows that 10,000 IU/day is generally safe for adults. HOWEVER, as a breastfeeding mother up north, over a number of months 10,000 IU/day raised my blood levels to 141, which is too high. Right around 70-80 is probably the safest ideal blood level, based on current knowledge. Blood levels should not be lower than 50, or your body is most likely chronically starved for vitamin D and not storing any (conventional labs are behind and still consider as low as 30 to be ok--it's not).
The Vitamin D Council currently recommends:
-children under 1: 1000 IU/day (note: I disagree with this IF baby is breastfed AND the breastfeeding mother's levels are adequate/supplemented. I did not supplement my son directly until he was 2, and he had adequate blood levels from my milk and the sun. My own blood levels were adequate with supplementation.)
-children over 1: 1000IU/day per 25 lbs body weight
-adults: 5000 IU/day
All to be followed by a blood test a few months later.
It really is important to get your blood levels checked (and continue to do so at least twice a year) because everyone metabolizes vitamin D differently, as Crystal said. Factors which tend to reduce metabolization of vitamin D include obesity, age, and taking statins.
http://www.vitamindcouncil.org/healt...eficient.shtml