The best way to get your Vitamin D is from sunshine and today is the day! Get out there and enjoy it while it lasts. Unless you are extremely susceptible to sunburn or have been told by your doctor to stay out of the sun, getting some rays in the morning and late afternoon when the sun isn't at its strongest is the best way to build up and store your Vitamin D for those greyer days. Wear a bikini as some sun on your stomach not only feels good, you are doing your body some good as well!  Make sure you are also getting a good amount of healthy fat in your diet such as olive or coconut oil in order to properly absorb Vitamin D.