That isn't so easy. I live in Norway. Where I am, winter days are only 4-5 hours long and the sun isn't all that strong. One can easily work through the sunligh

That isn't so easy. I live in Norway. Where I am, winter days are only 4-5 hours long and the sun isn't all that strong. One can easily work through the sunlight. In addition, you should be out with some skin exposed - more than just your face - for at least 15 minutes a day during daylight hours. In some areas, this makes it somewhat prohibitive during winter and you still might need supplements.