When I took the prescription 50K/wk, it was Vit D2. Not the D3 made by the body and it was useless. Never budged my levels, tried a number of rounds, but I was also on a low fat vegetarian diet at the time.
After going low carb, high fat, adding some coconut oil, and taking OTC 4-6,000 IU Vit D3 for about a year, tested over 50! The other difference was I stopped using sunscreen. I naturally now do not burn and stay out in sun much longer than before, sometimes using coconut oil on my skin as well.
Getting sun makes Vit D, which protects you from sun. Nature again gets it right. http://www.marksdailyapple.com/8-na.../#axzz1r58Fvffj

For a more scientific look at sunlight, Dr BarrY Groves had a good article with a focus on cancer. http://second-opinions.ginwiz.com/l.../sunlight.html/