Publications, articles and studies done more than 2 years ago may not correspond with the latest research anymore!
Some countries (like USA) use ng/ml for Vit D measurement. Ng/ml times 2.5 get you to nmol/L.
Recommended book:
The Vitamin D revolution by Soram Khalsa (2009) ISBN: 978-1-4019-2470-6
Links
http://en.wikipedia.org/wiki/Vitamin_D
http://www.telegraph.co.uk/health/healthnews/6214958/Vitamin-D-can-boost-survival-from-cancer.html