One thing that is not being mentioned in many sources is the need for provitamin A along with vitamin D3.
Even natural sunlight will drive A levels down and A and D are needed together.
Because of this- my family uses a high vitamin A cod liver oil (and skate oil for me) along with liqui D 3 (that is another thing not being mentioned- all the studies on D3 were done with a liquid form).
I give my youngest children 6 -10 thousand IU's daily. I myself take many times that (my level was once 12 and optimal for me will be over 100).
Cheap tests are available as well and I suggest testing.
Sources for good quality D3 (I prefer a pure olive oil base)
http://www.healthegoods.com/natural-...vitramins.html
Sources for high quality CLO-
http://www.greenpasture.org/community
Some info on vitamin D (and A)
http://www.westonaprice.org/basicnut...fications.html
http://www.westonaprice.org/basicnut...ndmiracle.html