There's nothing like a sunny day to fill up on vitamin D. Studies show that when 22 percent of unprotected skin (no clothing or sunscreen) is exposed to the sun, 1000 IU of vitamin D is synthesized in 10-15 minutes. The Recommended Dietary Allowance (RDA) for adults ranges from 600 to 800 IU daily. But when the clouds roll in or the days are too cold to expose skin to the sunshine, it's time to supplement your diet with foods high in vitamin D, such as salmon, tuna fish, sardines, cod ... Full Article