I have teenagers and wonder the same thing.
Further up in the thread, or maybe on another one, 2,000 units of Vitamin D are thought to be effective with the symptoms.
You may be thinking of these two references to Vitamin D from a thread a few days ago.
http://www.freerepublic.com/focus/f-news/2237216/posts?page=67#67
http://www.freerepublic.com/focus/f-news/2237216/posts?page=51#51