Evidence from clinical trials shows, with a wide margin of confidence, that a prolonged intake of 10,000IU/d of vitamin D3 poses no risk of adverse effects for adults, even if this is added to a rather high physiologic background level of vitamin D.
Vitamin D and cancer mini-symposium: the risk of additional vitamin D.
Vieth R.\nAnn Epidemiol. 2009 Jul;19(7):441-5. Epub 2009 Apr 11.
PMID: 19364661
doi:10.1016/j.annepidem.2009.01.009
Meta-analysis: longitudinal studies of serum vitamin D and colorectal cancer risk.
Yin L, Grandi N, Raum E, Haug U, Arndt V, Brenner H.
Aliment Pharmacol Ther. 2009 Jul 1;30(2):113-25. Epub 2009 Apr 15.
PMID: 19392870
DOI: 10.1111/j.1365-2036.2009.04022.x
Conclusions Our results support suggestions that serum 25(OH)D is inversely related to CRC risk.
How to optimize vitamin D supplementation to prevent cancer, based on cellular adaptation and hydroxylase enzymology.
Vieth R.
Anticancer Res. 2009 Sep;29(9):3675-84. Review.
PMID: 19667164