Half of adults are vitamin D deficient

http://well.blogs.nytimes.com/2010/02/01/the-miracle-of-vitamin-d-sound-science-or-hype/?em

Each of us really needs to go out in direct sunlight at least 10 minutes per day or go to a tanning salon for about 15 minutes once a week. We also need to eat oily fish like sardines and mackerel at least a couple of times a week.

http://www.scientificamerican.com/blog/post.cfm?id=another-reason-vitamin-d-is-importa-2010-03-07