I have been following the Breast Cancer Vitamin D association for some time now and logging the research [url-http://brain.hastypastry.net/forums/showthread.php?t=2890]here[/url] I am convinced that having optimal vitamin d status, over 125nmol/L -130nmol/L is associated with 50% less incidence and a better prognosis for those with the higher status.
How this is achieved is a matter of choice but if you live in the UK it really isn't sensible to rely on sunshine. That will be fine for 30 days a year but not for 365. We just don't have a sufficient number of days when it's practicable to lay naked in the sun and soak up UVB even for the mere 20minutes that is necessary to achieve our 4000iu/daily requirement.
The choice is then between sunlamps and supplements. While supplements are effective they don't allow your largest organ (skin) to function as nature intended. 85% of our Vitamin D isn't metabolised by our liver/kidneys it's processed by the skin and other 50+ tissues on-site, where needed, when needed.
Our bodies evolved with a
feedback mechanism that rewards us for spending time under UVB. The more I think about it, the more I understand the importance of Vitamin D, the more convinced I am that regular
limited UVB exposure is necessary for optimal health.