Sanjay Gupta on the Vitamin D Debate
Time Mag May 18 2009 http://www.time.com/time/magazine/article/0,9171,1896749,00.html#ixzz0bInfiwQ5 
A lot changed in between the births of my second and third daughters. For one thing, this time around I really am getting no sleep; for another, the pediatrician recommended something for our 1-month-old that is different from what had been suggested for our other children. She said we needed to pick up a liquid multivitamin that contains 400 international units (IUs) of vitamin D. It was a little confusing, because with our first daughter, now almost 4, the doctor told us to simply get her out in the sun from time to time to let her body produce vitamin D, also known as the sunshine vitamin. When our second child was born two years ago, we were told to give her a multivitamin that had 200 IUs of vitamin D. And now another change. So, what gives with vitamin D, and what do we really know about its risks and benefits?
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. 
Amid all this new evidence, the Institute of Medicine (IOM) has assembled a panel of experts to re-evaluate just how much vitamin D we really need and can safely tolerate. Current IOM recommendations, set in 1997, are 200 IUs a day from birth to age 50 and a bit more after that. The upper limit of safety, according to the institute, is 2,000 IUs daily--too much can lead to, among other things, nausea and kidney stones--yet some vitamin-D proponents are pushing for up to 4,000 IUs a day for adults.
The IOM review won't be completed until May 2010. In the meantime, Dr. Frank Greer, chairman of the nutrition committee at the American Academy of Pediatrics, is confident that the academy's new guideline of 400 IUs is enough for kids under 2. But, he wonders, &quot;what about adolescents? Do they need 800?&quot; That remains to be seen. He takes 1,000 IUs daily.
In addition to the question of how much vitamin D, there is 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). And, of course, there is always cod-liver oil. Good luck trying to get your kids to swallow that.
— With reporting by Shahreen Abedin