Your post is at odds with the testimony of many here who know from direct and long experience it is not true.
At daily levels in excess of 2000 iu per day good things begin to happen. Sickness dissipates or ceases. When there is a possibility or probability of cold or sinus an increase over the 2000 iu threshold for a few days or a week will likely eliminate the threat.
You have read...... your problem is that your one source research is trivial compared to a very large host of other sources available here on Free republic over a long period.Your skepticism is noteworthy but is unwarranted.
Blam has posted several additional sources here today.
Here are more. The first was posted on Free Republic years ago and is especially compelling
http://www.medicalnewstoday.com/articles/51913.php
http://www.freerepublic.com/focus/f-chat/1929828/posts
http://www.freerepublic.com/focus/f-chat/2699123/posts
http://www.freerepublic.com/focus/f-chat/2699364/posts
http://www.freerepublic.com/focus/f-news/2703355/posts
http://www.freerepublic.com/focus/chat/2452507/posts?page=23#23
http://pajamasmedia.com/blog/sunshine-vitamin-d-and-death-by-scientific-consensus/
http://www.vitamindcouncil.org/
http://www.medicalnewstoday.com/articles/51913.php
When I come across information from what I believe is a credible source and will be of interest to Freepers, I post it. There are many health issues that are not settled, by any means, and it’s helpful to have as much info as possible.
Freegards,
Pining