"The Vitamin-D Debate," Sanjay Gupta, Time, May 18, 2009.

"Turns out the debate about how much vitamin D we need has intensified over the past 10 years.  One part of the discourse focuses on the growing body of research that points to numerous health benefits of the chemical (actually a hormone): it can help prevent rickets in children and severe bone loss in adults and potentially lowers the risk of multiple sclerosis, juvenile diabetes, cancer, heart disease, colds and influenza...

In addition to the question of how much vitamin D, there is a debate over the best way to get it.  About 10 to 15 minutes spent outside in full sun will give a fair-skinned person dressed only in his skivvies 10,000 to 20,000 IUs.  Some vitamin D advocates point to the vigorous use of sunscreen as the reason studies show that so many Americans don't get enough D.  But we don't want taking advantage of the potential benefits of vitamin D to mean increased risk of contracting skin cancer.  In addition to supplements, there are foods that naturally contain vitamin D (salmon, egg yolks, liver) and others that are fortified with it (milk, cereals, juices, breads)..."