Vitamin D id vital for our bodies, yet it is something we don't get enough of. You COULD take supplements...and in the winter that may be a good choice. BUT, you can get a good dose just by going out and getting bit of sun each day. 15 to 30 minutes once or twice a day will restock your system and get you feeling good, throw in a bit of walking or other exercise and you have a recipe for success!
