My Dr. put me on 25,000 daily for two weeks and then decreased it to 10,000 a day during the winter. Getting 15 min of sun on 25% of your body you get over 25,000 units. During good weather I make it a priority to sit in the sun for 20 min with bare arms and legs. A simple blood test will show a vitamin D deficiency but you have to ask for it. Most Dr.s don't think about it or dismiss it thinking you get enough with foods and sun. If you aren't in the sun at all you need vitamin D in amounts you can't get in foods. Also vitamin C is important, way over the recommended amounts set as standard. Humans and frogs are the only animal species that cannot make their own vitamin C. Too much to go into but Vitamin C is very important on a daily basis. Ester C is the best for absorption. Vitamins and bright lights and you should be in a good mood all winter.