The RDA is too low  Vieth traced why
Clipped from http://www.vitaminsinamerica.com/news/vitamin_d.htm#contra 
How could the current government figures be so far off?
Vieth traced back how it happened. The 1989 US nutrition guidelines said that 5 times the RDA for vitamin D may be harmful - in other words, don't take more than 1000 IU/d. It cited a 1963 "expert committee report", which itself referred back to a 1938 report, in which linear bone growth in infants was suppressed in those given 1800-6300 IU vitamin D/d. But this citation is meaningless in relation to adult nutrition.
Vieth also traced back a statement from the 1987 Council Report for the American Medical Association that "dosages of 10,000 IU/d for several months have resulted in marked disturbances in calcium metabolism...and, in some cases, death."  This report cited two references, and Vieth says of these: "One was a review article about vitamins in general, which gave no evidence for and cited no other reference to its claim of toxicity at vitamin D doses as low as 250 µg (10000 IU)/d . The other paper cited in the report dealt with 10 patients with vitamin D toxicity reported in 1948, for whom the vitamin D dose was actually 3750-15000 µg (150000-600000 IU)/d, and all patients recovered." He goes on to say: "If there is published evidence of toxicity in adults from an intake of 250 µg (10000 IU)/d, and that is verified by the 25(OH)D concentration, I have yet to find it.”

Ref Reinhold Vieth, Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety1,2, American Journal of Clinical Nutrition, Vol. 69, No. 5, 842-856, May 1999, (http://www.ajcn.org/cgi/content/full/69/5/842 )   PDF on VitaminDWiki.com